The biochemical and neuroendocrine bases of the hyperalgesic nocebo effect

Allergy-like nocebo events reported with COVID-19 vaccines: a case control study

BACKGROUND

Allergy-like symptoms after COVID-19 vaccination are frequently reported, though true allergic reactions are rare. Clinical trials suggest many reported symptoms may reflect nocebo effects. This study aimed to characterize nocebo responses and identify associated factors.

RESEARCH DESIGN AND METHODS

A case-control study was conducted using pharmacovigilance records and a cross-sectional questionnaire. Cases were defined as patients reporting allergy-like symptoms without anaphylaxis; controls reported reactogenicity or localized reactions. Data on demographics, medical history, vaccinations, and psychological factors were analyzed using multivariate logistic regression to identify risk factors associated with nocebo effects.

RESULTS

Among 1038 participants, 320 were nocebo cases and 718 were controls. Cases frequently reported cutaneous (71.8%) and respiratory (38.8%) symptoms, with 43.4% occurring after the first dose. Nocebo responses were positively associated with a history of allergy (OR 1.78, 95% CI: 1.32-2.4) and COMIRNATY vaccine (OR 1.60, 95% CI: 1.20-2.14), and negatively correlated with perceived vaccine effectiveness (OR 0.93, 95% CI: 0.88-0.98).

CONCLUSIONS

The nocebo effect appears to differ by vaccine type and is more common in individuals with a history of allergy and lower perceived vaccine effectiveness. While further research is needed to validate these findings, this underscores the importance of clear, evidence-based communication to reduce nocebo responses.

Hypercapnia Reduces Perceived Heat Pain in Healthy Subjects

BACKGROUND

Danger signals modulate pain perception. Both amplification and attenuation of perceived pain are observed in healthy subjects exposed to danger signals, such as transient threats of an imminent electrical shock. However, exposure to danger signals in real life typically is not transient but constant over minutes to hours. Here, this was experimentally achieved by administering hypercapnic air (7.5% CO2). The primary objective was to investigate whether perceived heat pain would be differentially modulated during this intervention compared to regular air administration. The secondary objective assessed the potential differences of such a modulation with respect to heat intensity level.

METHODS

Thirty-eight participants (19 women) received two air mixtures (hypercapnic and regular air) for 13 min each, during which 18 (6 × 3) noxious heat stimuli of three different intensities were applied to the calf and rated on two scales (intensity and pleasantness/unpleasantness). Psychological and physiological states were compared between conditions using the body sensations questionnaire, self-assessment manikins, heart rate, and galvanic skin response. Statistical analyses were performed using Bayesian estimation testing.

RESULTS

Between-condition differences were statistically meaningful for all heat intensity levels, always showing reduced pain perception during hypercapnia compared to normocapnia. The magnitude of the observed hypoalgesia did not depend on heat intensity levels.

CONCLUSIONS

The presence of a continuous physiological danger signal results in hypoalgesia. Future studies need to determine whether the present results only hold for hypercapnia in healthy subjects or are generalisable to interactions between pain perception and continuous physiological danger signals in clinical pain populations.

SIGNIFICANCE STATEMENT

It was shown that hypercapnia leads to reduced perception of noxious heat stimuli. If confirmed by neural data in future studies this could help to better understand the interaction of pain perception and continuous physiological danger signals in clinical pain conditions, potentially allowing for improved treatment of affected individuals.

Negative expectations and related nocebo effects in shoulder pain: a perspective for clinicians and researchers

The nocebo effect, a phenomenon wherein negative expectations can worsen symptoms, is increasingly acknowledged within the context of musculoskeletal conditions. While experimental evidence has, to some extent, examined negative expectations in shoulder pain, their specific relationship with nocebo effects and their manifestation in clinical practice remains unexplored. In this perspective, clinicians and researchers are guided by first examining the psychobiology and neurophysiology underlying nocebo effects from a basic science standpoint, thereby equipping clinicians with a robust understanding of the phenomenon. What are considered the primary potential sources of nocebo effects in individuals with shoulder pain are then outlined - namely, diagnostic labels, diagnostic imaging and special tests, the medicalization of normality, and overtreatment. Practical clinical strategies are subsequently proposed to mitigate nocebo effects arising from these sources. Finally, the research implications for advancing the study of nocebo effects in people with shoulder pain are discussed. Overall, this perspective provides a comprehensive overview of the impact of negative expectations and associated nocebo effects on shoulder pain outcomes. By identifying potential sources of nocebo effects that may emerge in everyday clinical practice, guidance on mitigating related negative expectations in patients with shoulder pain is offered.

Visual placebo and nocebo effects

Placebo and nocebo effects modulate symptom perception through expectations and learning processes in various domains. Predominantly, their impact has been investigated on pain and physical performance. However, the influence of placebos and nocebos on visual system functionality has yet to be explored. The present study aimed to test whether placebo and nocebo effects can intervene in altering participants' performance outcomes during a novel visual accuracy task and to examine the underlying neural mechanisms through EEG. After performing a baseline session, visual accuracy was said to be enhanced or disrupted by a sham transcranial electrical stimulation over the occipital lobe. Behavioural results showed a significant increase in visual accuracy for the placebo group, from the baseline session to the test session, whereas the nocebo group showed a decrease in visual accuracy. EEG analyses on the event-related potential P300 component, conducted on both a centro-parietal electrode patch and a parieto-occipital, one displayed an increase in the amplitude of P300 for the placebo group, and a decrease in the nocebo group. These findings suggest for the first time that placebo and nocebo effects can influence visual perception and attentional processes linked to it. Overall, the present study contributes to understanding how expectations affect sensory perception beyond pain and the motor system, paving the way for investigating these phenomena in other sensory modalities such as auditory or olfactory perception. KEY POINTS: Placebo and nocebo effects have been studied predominantly in pain and motor performance fields. In a novel visual task, the impact of placebo and nocebo effects on the visual system has been evaluated, in both early components (stimuli-related) and late components (attention-related). The placebo group showed an increase in visual accuracy and EEG-evoked potential amplitudes, whereas the nocebo group showed a decrease in both. This study shows how expectations and the related placebo and nocebo effects can shape basic stimuli sensory perception in the visual domain.

Placebo effects in neuropathic pain conditions

Management of neuropathic pain is exceptionally challenging and development of new drugs and ways to optimize treatment effects in clinical practice are needed. Over the last decade, some of the mechanisms underlying placebo effects have been elucidated and some of the insights have the potential to improve the treatment for neuropathic pain. Research suggests that the increasing placebo responses observed in randomized controlled trials (RCTs) for neuropathic pain pose challenges for the development and availability of new effective pain medications. In neuropathic pain, these placebo responses are typically not controlled for the natural history of pain and other confounding factors. Thus, our knowledge about the magnitude and mechanisms of placebo effects in neuropathic pain is sparse. A few mechanistic studies investigating placebo effects by controlling for natural history of pain have found large placebo analgesia effects in neuropathic pain. Psychological factors such as expectations and emotions play a substantial role in inducing the placebo effects. Here, we review placebo effects and the psychological and neurobiological mechanisms contributing to the placebo effects. The knowledge obtained from studies of placebo mechanisms can help improve the information that can be obtained from RCTs and potentially improve development of new pain medications and optimize treatment of neuropathic pain in clinical practice.

Neural mechanisms underlying placebo and nocebo effects in tonic muscle pain

Pain is a highly subjective and multidimensional experience, significantly influenced by various psychological factors. Placebo analgesia and nocebo hyperalgesia exemplify this influence, where inert treatments result in pain relief or exacerbation, respectively. While extensive research has elucidated the psychological and neural mechanisms behind these effects, most studies have focused on transient pain stimuli. To explore these mechanisms in the context of tonic pain, we conducted a study using a 15-minute tonic muscle pain induction procedure, where hypertonic saline was infused into the left masseter of healthy participants. We collected real-time Visual Analogue Scale (VAS) scores and functional magnetic resonance imaging (fMRI) data during the induction of placebo analgesia and nocebo hyperalgesia via conditioned learning. Our findings revealed that placebo analgesia was more pronounced and lasted longer than nocebo hyperalgesia. Real-time pain ratings correlated significantly with neural activity in several brain regions. Notably, the putamen was implicated in both effects, while the caudate and other regions were differentially involved in placebo and nocebo effects. These findings confirm that the tonic muscle pain paradigm can be used to investigate the mechanisms of placebo and nocebo effects and indicate that placebo analgesia and nocebo hyperalgesia may have more distinct than common neural bases.

The downside to choice: instrumental control increases conditioned nocebo hyperalgesia

ABSTRACT

Nocebo hyperalgesia is a pervasive problem in which the treatment context triggers negative expectations that exacerbate pain. Thus, developing ethical strategies to mitigate nocebo hyperalgesia is crucial. Emerging research suggests that choice has the capacity to reduce nocebo side effects, but choice effects on nocebo hyperalgesia have not been explored. This study investigated the impact of choice on conditioned nocebo hyperalgesia using a well-established electrocutaneous pain paradigm where increases in noxious stimulation were surreptitiously paired with the activation of a sham device. In study 1, healthy volunteers (N = 104) were randomised to choice over (nocebo) treatment administration, nocebo administration without choice, or a natural history control group. Nocebo hyperalgesia was greater for those with choice than no choice, suggesting that choice increased rather than diminished nocebo hyperalgesia. Study 2 tested whether providing positive information about the benefits of choice in coping with pain could counteract heightened nocebo hyperalgesia caused by choice. A different sample of healthy adults (N = 137) were randomised to receive nocebo treatment with choice and positive choice information, choice only, or no choice. The positive choice information failed to attenuate the effect of choice on nocebo hyperalgesia. The current results suggest that, rather than decreasing nocebo hyperalgesia, treatment choice may exacerbate pain outcomes when a painful procedure is repeatedly administered. As such, using choice as a strategy to mitigate nocebo outcomes should be treated with caution.

What should constitute a control condition in psychedelic drug trials?

Over the past decade there has been a surge in interest in placebo-controlled trials using non-classical 3,4-methylenedioxymethamphetamine (MDMA) and classical psychedelics such as psilocybin, lysergic acid diethylamide (LSD) and N,N-dimethyltryptamine (DMT) to treat neuropsychiatric disorders. However, the success and reliability of these trials depend on the design of the trials, the choice of control conditions, and the ability to blind both participants and researchers. When appropriate control conditions are lacking, it becomes difficult to disentangle placebo and expectation effects from medication effects. Here we explore the neurobiology of placebo and expectation effects, alongside the methodological considerations for selecting suitable control conditions in psychedelic trials. This includes examining the advantages and disadvantages of various control conditions and proposing new directions to enhance the validity of these trials and their regulatory science. By addressing these factors, we aim to improve the reliability of psychedelic research in uncovering the therapeutic benefits of psychedelics beyond placebo and expectation effects.

The Role of Pain Expectations in the Development of Secondary Pinprick Hypersensitivity: Behavioral-Neurophysiological Evidence and the Role of Pain-Related Fear

Secondary mechanical hypersensitivity, a common symptom of neuropathic pain, reflects increased responsiveness of nociceptive pathways and can be induced temporarily in healthy volunteers using high-frequency electrical stimulation of the skin. Expectations modulate acute pain perception and fear of pain has been shown to attenuate and amplify the placebo and nocebo effects, respectively. However, the role of expectations and fear in the development of mechanical secondary hypersensitivity remains unclear. The modulatory role of fear and expectations in the development of mechanical secondary hypersensitivity remains so far mainly correlational. Here, we randomly assigned healthy participants (women) to a placebo, nocebo, or control group. In the experimental groups, participants' expectations of pain were manipulated using verbal suggestions accompanied by an inert treatment. Fear of pain was evaluated both in terms of fear of pain and via questionnaires. Sensitivity to mechanical stimulation was assessed by self-reported pinprick ratings before and after high-frequency stimulation; pinprick-evoked potentials elicited by the stimulation were recorded. The placebo group developed the least mechanical secondary hypersensitivity (smaller proximal-distal spread), while the nocebo group developed the most, but only when outliers were excluded. Higher expectations of pain predicted a greater development of mechanical secondary hypersensitivity. Anticipatory pain-related fear only mediated the relationship between unpleasantness expectations and perceived pinprick unpleasantness. Dispositional fear of pain moderated the relationship between expectations and the perceived intensity and unpleasantness of pinpricks. No group differences were observed in pinprick-evoked potentials. We provide preliminary evidence that both expectations and fear impact the development of mechanical secondary hypersensitivity. PERSPECTIVE: Expectations of pain may influence the development of secondary mechanical hypersensitivity. This effect is moderated by dispositional fear of pain and partially mediated by situational fear of pain.

The role of self-reported and physiological stress in nocebo hyperalgesia

Negative expectations can increase pain sensitivity, leading to nocebo hyperalgesia. However, the physiological and psychological factors that predispose individuals to this phenomenon are still not well understood. The present study examined whether stress induced by a social stressor affects nocebo hyperalgesia, and whether this effect is mediated by self-reported and physiological stress responses. We recruited 52 healthy participants (15 men) who were randomly assigned to either the Trier Social Stress Test (TSST) or a control condition (a friendly version of the TSST). Nocebo hyperalgesia was induced using negative suggestions combined with a validated pain conditioning paradigm. We assessed self-reported (anxiety and stress) and physiological (cortisol, alpha-amylase, heart rate, and skin conductance) responses to stress. Both groups exhibited significant nocebo hyperalgesia. The stress group showed higher levels of anxiety, self-reported stress, and cortisol levels compared to the control group while no significant differences were found in other physiological markers. The stress and control groups did not differ in the magnitude of nocebo hyperalgesia, but anxiety levels partially mediated the effects of the stress test on nocebo hyperalgesia. Our findings suggest that an external social stressor does not directly affect nocebo hyperalgesia, but that increased anxiety due to the stressor enhances its magnitude. Thus, it may be worthwhile to investigate whether reducing stress-related anxiety in clinical settings would help alleviate nocebo effects.

Risk factors associated with nocebo effects: A review of reviews

Objective

This meta-review aims to identify and categorize the risk factors that are associated with nocebo effects. The nocebo effect can exert a negative impact on treatment outcomes and have detrimental outcomes on health. Learning more about its potential predictors and risk factors is a crucial step to mitigating it.

Methods

Literature review studies about the risk factors for nocebo effects were searched through five databases (PubMed, Scopus, The Cochrane Library, PsycINFO, and Embase) and through grey literature. Methodological validity and risk of bias were assessed. We conducted a thematic analysis of the results of the forty-three included reviews.

Results

We identified nine categories of risk factors: prior expectations and learning; socio-demographic characteristics; personality and individual differences; neurodegenerative conditions; inflammatory conditions; communication of information and patient-physician relationship; drug characteristics; setting; and self-awareness. We also highlighted the main biochemical and neurophysiological mechanisms underlying nocebo effects.

Conclusions

Nocebo effects arise from expectations of adverse symptoms, particularly when triggered by previous negative experiences. A trusting relationship with the treating physician and clear, tailored treatment instructions can act as protective factors against a nocebo effect. Clinical implications are discussed.

Exploring the Impact of Affinity and Unpleasantness on Conditioned Pain Modulation among Healthy Individuals

The variability of the Conditioned Pain Modulation (CPM) effect can be attributed to conditioning stimulus (CS) characteristics, such as intensity, duration, unpleasantness, or affinity. This study investigates the impact of affinity and unpleasantness variables on the CPM effect using two protocols (cold water and ischemia) in the same healthy individuals (n = 54). Additional variables were also examined for their potential influence on the CPM effect. The main results are as follows: (1) a higher level of affinity and a lower level of unpleasantness for the stimuli used resulted in a stronger CPM effect; (2) significant differences were observed in the extreme categories (high and low) of both variables, whereas the 'indifferent' group did not show a clear trend; (3) within-subject analysis demonstrated that affinity for the CS had a clear impact on the CPM effect; (4) no correlations were found between the CPM effect and the additional variables, except for the extraversion variable with the CPM effect of the ischemia protocol, and CS duration variable with CPM effect in the cold water protocol; and (5) only the affinity variable explained the CPM effect in both protocols in the multiple linear regression analysis. The affinity variable was found to influence the CPM effects significantly, indicating its important role in our perception and response to pain.

Sodium bicarbonate induces alkalosis, but improves high-intensity cycling performance only when participants expect a beneficial effect: a placebo and nocebo study

The study aimed to investigate the effects of sodium bicarbonate (NaHCO3) intake with divergent verbal and visual information on constant load cycling time-to-task failure, conducted within the severe intensity domain. Fifteen recreational cyclists participated in a randomized double-blind, crossover study, ingesting NaHCO3 or placebo (i.e., dextrose), but with divergent information about its likely influence (i.e., likely to induce ergogenic, inert, or harmful effects). Performance was evaluated using constant load cycling time to task failure trial at 115% of peak power output estimated during a ramp incremental exercise test. Data on blood lactate, blood acid-base balance, muscle electrical activity (EMG) through electromyography signal, and the twitch interpolation technique to assess neuromuscular indices were collected. Despite reduced peak force in the isometric maximal voluntary contraction and post-effort peripheral fatigue in all conditions (P < 0.001), neither time to task failure, EMG nor, blood acid-base balance differed between conditions (P > 0.05). Evaluation of effect sizes of all conditions suggested that informing participants that the supplement would be likely to have a positive effect (NaHCO3/Ergogenic: 0.46; 0.15-0.74; Dextrose/Ergogenic: 0.45; 0.04-0.88) resulted in improved performance compared to control. Thus, NaHCO3 ingestion consistently induced alkalosis, indicating that the physiological conditions to improve performance were present. Despite this, NaHCO3 ingestion did not influence performance or indicators of neuromuscular fatigue. In contrast, effect size estimates indicate that participants performed better when informed that they were ingesting an ergogenic supplement. These findings suggest that the apparently ergogenic effect of NaHCO3 may be due, at least in part, to a placebo effect.

The Role of a Cholecystokinin Receptor Antagonist in the Management of Chronic Pancreatitis: A Phase 1 Trial

Chronic pancreatitis (CP) is a rare but debilitating condition with an 8-fold increased risk of developing pancreatic cancer. In addition to the symptoms that come from the loss of endocrine and exocrine function in CP, the management of chronic pain is problematic. We previously showed that the CCK-receptor antagonist called proglumide could decrease inflammation, acinar-ductal metaplasia, and fibrosis in murine models of CP. We hypothesized that proglumide would be safe and diminish pain caused by CP. A Phase 1 open-labeled safety study was performed in subjects with clinical and radiographic evidence of CP with moderate to severe pain. After a 4-week observation period, the subjects were treated with proglumide in 400 mg capsules three times daily (1200 mg per day) by mouth for 12 weeks, and then subjects returned for a safety visit 4 weeks after the discontinuation of the study medication. The results of three pain surveys (Numeric Rating Scale, COMPAT-SF, and NIH PROMIS) showed that the patients had significantly less pain after 12 weeks of proglumide compared to the pre-treatment observation phase. Of the eight subjects in this study, two experienced nausea and diarrhea with proglumide. These side effects resolved in one subject with doses reduced to 800 mg per day. No abnormalities were noted in the blood chemistries. A blood microRNA blood biomarker panel that corresponded to pancreatic inflammation and fibrosis showed significant improvement. We conclude that proglumide is safe and well tolerated in most subjects with CP at a dose of 1200 mg per day. Furthermore, proglumide therapy may have a beneficial effect by decreasing pain associated with CP.

Translating knowledge on placebo and nocebo effects into clinical practice

Introduction

Positive and negative treatment expectations are powerful modulators of health and treatment outcomes. A substantial part of treatment success is due to contextual factors modulating patient's expectations towards a treatment. Consequently, treatment expectations should be a target of therapeutic interventions themselves.

Objectives

This article highlights the neurobiological underpinnings of treatment expectations as well as strategies to modulate contextual factors to optimize treatment outcomes in daily clinical settings.

Methods

This clinical update aligns with the 2022 IASP Global Year Translating Pain Knowledge into Practice and selectively reviews the best available evidence and practice.

Results

The effects of treatment expectations, also known as placebo and nocebo effects, are observed in various clinical conditions and physiological systems. However, most of our knowledge comes from the field of pain, where expectation effects substantially contribute to overall analgesic treatment outcomes. Experimental placebo analgesia paradigms provide the best illustration of how analgesic effects can be attributed not only to a pharmacological or specific treatment, but instead are the result of the expectation towards the treatment. The impact of expectations on treatment outcome is highly variable between individuals, and the identification of factors predicting an individual's response has proven to be challenging. Further research is required to provide personalized treatment strategies for the daily clinical practice.

Conclusion

Patient's previous experiences and expectations are powerful modulators of treatment efficacy, tolerability, and adherence. By providing a comprehensive overview of recent advances in this field, this review offers valuable insights for clinicians and researchers seeking to improve patient-clinician interaction.

Negative expectations (nocebo phenomenon) in clinical interventions: A scoping review

Unpredictable, undesirable, and confusing reactions in the face of psychological or medical interventions make the clinical presentation more complicated and may represent clinically unexplained symptoms and also disturbed the doctor-patients relationship and decrease patients' benefits of treatment. It seems that negative expectations from the treatment (nocebo phenomenon) can explain such reactions. The aim of the current study is a scoping review and investigate different aspects of the nocebo phenomenon (negative expectations) in clinical interventions. This paper follows a scoping review of the existence, importance, and multidimensions of the nocebo phenomenon in medical and psychological interventions. Data sources include literature databases (ProQuest, PubMed, Google Scholar, and Scopus) reviewed from inception dates to 2023, and the terms negative expectations, nocebo effect, placebo effect, negative placebo, and clinical interventions were searched. The review of the available articles showed that negative expectations play an important role in the process and effectiveness of clinical interventions. Negative expectations (here named nocebo effect) can significantly interfere with rapport and treatment processes. Some underlying components of the nocebo effect include negative expectancies, conditioning, social learning, memory, cognitive distortions, meaning, motivation, somatic focus, negative reinforcements, personality, anxiety, and neurophysiological factors such as CCK, dopamine, and cortisol are proposed for development and presence of nocebo phenomenon in clinical practice. Negative expectations with its biopsychosocial aspects play an important and amazing role in disorganizing medical and psychological interventions. Using appropriate methods to reduce nocebo effects in therapeutic interventions may increase treatment compliance and adherence and increase the effectiveness of interventions.

A new experimental rat model of nocebo-related nausea involving double mechanisms of observational learning and conditioning

AIM

The nocebo effect, such as nausea and vomiting, is one of the major reasons patients discontinue therapy. The underlying mechanisms remain unknown due to a lack of reliable experimental models. The goal of this study was to develop a new animal model of nocebo-related nausea by combining observational learning and Pavlovian conditioning paradigms.

METHODS

Male Sprague-Dawley rats with nitroglycerin-induced migraine were given 0.9% saline (a placebo) or LiCl (a nausea inducer) following headache relief, according to different paradigms.

RESULTS

Both strategies provoked nocebo nausea responses, with the conditioning paradigm having a greater induction impact. The superposition of two mechanisms led to a further increase in nausea responses. A preliminary investigation of the underlying mechanism revealed clearly raised peripheral and central cholecystokinin (CCK) levels, as well as specific changes in the 5-hydroxytryptamine and cannabinoid systems. Brain networks related to emotion, cognition, and visceral sense expressed higher c-Fos-positive neurons, including the anterior cingulate cortex (ACC), insula, basolateral amygdala (BLA), thalamic paraventricular nucleus (PVT), hypothalamic paraventricular nucleus (PVN), nucleus tractus solitarius (NTS), periaqueductal gray (PAG), and dorsal raphe nucleus-dorsal part (DRD). We also found that nausea expectances in the model could last for at least 12 days.

CONCLUSION

The present study provides a useful experimental model of nocebo nausea that might be used to develop potential molecular pathways and therapeutic strategies for nocebo.

The Nocebo Effect

Adverse nocebo responses can cause harm to patients and interfere with treatment adherence and effects in both clinic practice and clinical trials. Nocebo responses refer to negative outcomes to active medical treatments in clinical trials or practice that cannot be explained by the treatment's pharmacologic effects. Negative expectancies and nocebo effects are less known than placebo responses. Nocebo effects can be triggered by verbal suggestions, prior negative experiences, observation of others experiencing negative outcomes, and other contextual and environmental factors. As research advances over the years, mechanistic knowledge is accumulating on the neurobiological mechanisms of nocebo effects. This review summarizes studies on different facets of nocebo effects and responses and discusses clinical implications, ethical considerations, and future directions.

The Roles of Endogenous Opioids in Placebo and Nocebo Effects: From Pain to Performance to Prozac

Placebo and nocebo effects have been well documented for nearly two centuries. However, research has only relatively recently begun to explicate the neurobiological underpinnings of these phenomena. Similarly, research on the broader social implications of placebo/nocebo effects, especially within healthcare delivery settings, is in a nascent stage. Biological and psychosocial outcomes of placebo/nocebo effects are of equal relevance. A common pathway for such outcomes is the endogenous opioid system. This chapter describes the history of placebo/nocebo in medicine; delineates the current state of the literature related to placebo/nocebo in relation to pain modulation; summarizes research findings related to human performance in sports and exercise; discusses the implications of placebo/nocebo effects among diverse patient populations; and describes placebo/nocebo influences in research related to psychopharmacology, including the relevance of endogenous opioids to new lines of research on antidepressant pharmacotherapies.

The relationship between expectancy, anxiety, and the nocebo effect: a systematic review and meta-analysis with recommendations for future research

Despite the theoretical prominence of expectancy and anxiety as potential mechanisms of the nocebo effect, not all studies measure expectancy and/or anxiety, and there are inconsistent findings among those that do. The present study sought to systematically review and meta-analyse available data to evaluate the relationship between expectancy, anxiety and the nocebo effect. The two key questions were: (1) whether nocebo manipulations influence expectancy and anxiety; and (2) whether expectancy and anxiety are associated with the subsequent nocebo effect. Fifty-nine independent studies (n = 3129) were identified via database searches to 1st August 2021. Nocebo manipulations reliably increased negative expectancy with a large effect (g = .837) and state anxiety with a small effect (g = .312). Changes in expectancy and state anxiety due to the nocebo manipulation were associated with larger nocebo effects (r = .376 and .234, respectively). However, there was no significant association between dispositional anxiety and the nocebo effect. These findings support theories that rely on situationally-induced expectancy and anxiety, but not dispositional anxiety, to explain nocebo effects. Importantly, being malleable, these findings suggest that interventions that target maladaptive negative expectancies and state anxiety could be beneficial for reducing the harm nocebo effects cause across health settings. Recommendations for future research are discussed.

How Do Expectations Modulate Pain? A Motivational Perspective

Expectations can profoundly modulate pain experience, during which the periaqueductal gray (PAG) plays a pivotal role. In this article, we focus on motivationally evoked neural activations in cortical and brainstem regions both before and during stimulus administration, as has been demonstrated by experimental studies on pain-modulatory effects of expectations, in the hope of unraveling how the PAG is involved in descending and ascending nociceptive processes. This motivational perspective on expectancy effects on the perception of noxious stimuli sheds new light on psychological and neuronal substrates of pain and its modulation, thus having important research and clinical implications.

Nocebo effects in visceral pain: concept and design of the experimental randomized-controlled pain study 'NoVis'

The role of psychological factors in the pathophysiology and treatment of chronic visceral pain in disorders of gut-brain interactions (DGBI) is increasingly appreciated. Placebo research has underscored that expectations arising from the psychosocial treatment context and from prior experiences shape treatment responses. However, effects of negative expectations, i.e., nocebo effects, as they are likely crucial elements of DGBI patients' clinical reality, have thus far only rarely been investigated in the context of visceral pain, with untapped potential for improved prevention and treatment. The experimental randomized-controlled pain study "NoVis," carried out within the Collaborative Research Center (CRC) 289 ("Treatment Expectation"), aims to close gaps regarding the generation and persistence of nocebo effects in healthy volunteers. It is designed to elucidate effects of negative expectations in a multiple-threat paradigm with intensity-matched rectal distensions and cutaneous thermal stimuli, allowing to test nocebo effects in the visceral and somatic pain modalities. Negative expectations are experimentally induced by elements of doctor-patient communication (i.e., instruction) and/or by surreptitious amplification of symptom intensity (i.e., experience/learning) within a treatment context. Accordingly, the repeated measures between-subject design contains the between-group factors "treatment instruction" (negative vs. control) and "treatment experience" (negative vs. control), with volunteers randomized into four experimental groups undergoing several pain stimulation phases (repeated factor). This allows to compare the efficacy of instruction vs. experience, and more importantly, their combined effects on the magnitude of negative expectations and their impact on pain responses, which we expect will be greatest for the visceral modality. After a Baseline, short-term effects are assessed during a test phase accomplished on study day 1 (Test-1 Phase). To explore the persistence of effects, a second test phase is accomplished 1 week later (Test-2 Phase). Effects of negative expectations within and across pain modalities are assessed at the subjective and objective levels, with a focus on psychophysiological and neuroendocrine measures related to stress, fear, and anxiety. Since nocebo effects can play a considerable role in the generation, maintenance, or worsening of chronic visceral pain, and may even constitute risk factors for treatment failure, knowledge from experimental nocebo research has potential to improve treatment outcomes in DGBI and other clinical conditions associated with chronic visceral pain.

Nocebo Hyperalgesia in Patients With Fibromyalgia and Healthy Controls: An Experimental Investigation of Conditioning and Extinction Processes at Baseline and 1-Month Follow-up

Nocebo effects are adverse treatment outcomes that are not ascribed to active treatment components. Potentially, their magnitude might be higher in patients with chronic pain compared to healthy controls since patients likely experience treatment failure more frequently. The current study investigated group differences in the induction and extinction of nocebo effects on pressure pain at baseline (N = 69) and 1-month follow-up (N = 56) in female patients with fibromyalgia and matched healthy controls. Nocebo effects were first experimentally induced via classical conditioning combined with instructions on the pain-increasing function of a sham transcutaneous electrical nerve stimulation device, then decreased via extinction. One month later, the same procedures were repeated to explore their stability. Results suggest that nocebo effects were induced in the healthy control group during baseline and follow-up. In the patient group, nocebo effects were only induced during follow-up, without clear group differences. Extinction was only observed during baseline in the healthy control group. Further comparisons of nocebo effects and extinction indicated no significant changes across sessions, possibly suggesting their overall magnitudes were stable over time and across groups. In conclusion, contrary to our expectations, patients with fibromyalgia did not have stronger nocebo hyperalgesia; instead, they might be less responsive to nocebo manipulations than healthy controls. PERSPECTIVE: The current study is the first to investigate group differences in experimentally manipulated nocebo hyperalgesia between chronic pain and healthy populations at baseline and 1-month follow-up. Since nocebo effects are common in clinical settings, their investigation in different populations is essential to explain and minimize their adverse effects during treatment.

The Biology of Placebo and Nocebo Effects on Experimental and Chronic Pain: State of the Art

(1) Background: In recent years, placebo and nocebo effects have been extensively documented in different medical conditions, including pain. The scientific literature has provided strong evidence of how the psychosocial context accompanying the treatment administration can influence the therapeutic outcome positively (placebo effects) or negatively (nocebo effects). (2) Methods: This state-of-the-art paper aims to provide an updated overview of placebo and nocebo effects on pain. (3) Results: The most common study designs, the psychological mechanisms, and neurobiological/genetic determinants of these phenomena are discussed, focusing on the differences between positive and negative context effects on pain in experimental settings on healthy volunteers and in clinical settings on chronic pain patients. Finally, the last section describes the implications for clinical and research practice to maximize the medical and scientific routine and correctly interpret the results of research studies on placebo and nocebo effects. (4) Conclusions: While studies on healthy participants seem consistent and provide a clear picture of how the brain reacts to the context, there are no unique results of the occurrence and magnitude of placebo and nocebo effects in chronic pain patients, mainly due to the heterogeneity of pain. This opens up the need for future studies on the topic.

Learned Nocebo Effects on Cutaneous Sensations of Pain and Itch: A Systematic Review and Meta-analysis of Experimental Behavioral Studies on Healthy Humans

OBJECTIVE

In past decades, the field of nocebo research has focused on studying how sensory perception can be shaped by learning. Nocebo effects refer to aggravated sensory experiences or increased sensitivity to sensations such as pain and itch resulting from treatment-related negative experiences. Behavioral conditioning and verbal suggestions of a negative treatment outcome may aggravate pain and itch perception. Gaining a comprehensive view of the magnitude of nocebo effects and contributing factors will help steer nocebo research toward fruitful directions for understanding complex sensory phenomena.

METHODS

We conducted a systematic review and meta-analysis of a total of 37 distinct experimental nocebo studies on healthy participants (all published in English between 2008 and 2021), with four separate meta-analyses for nocebo effects on pain or itch. We conducted subgroup analyses and meta-regression on factors such as type and intensity of sensory stimuli, and length of conditioning paradigms.

RESULTS

This meta-analysis showed that, on average, effect sizes of nocebo effects were moderate to large (Hedges g between 0.26 and 0.71 for the four primary outcomes). The combination of conditioning and verbal suggestions yielded stronger nocebo responses on pain in particular. Subgroup analyses, including factors such as the type of sensory stimulation, did not explain the moderate heterogeneity in nocebo magnitudes between different studies. Risk of bias was generally low and was not related to nocebo magnitudes either.

CONCLUSIONS

We discuss these results in relation to the role of conditioning and aversive learning, and we recommend more consistency in designing and reporting nocebo experiments.

Placebo effects in functional dyspepsia: Causes and implications for clinical trials

Placebo responses to an apparently inactive intervention are of interest from a scientific perspective as they suggest possible mechanism(s) at work beyond the intervention itself. They are also of interest from a clinical trials perspective since high rates of placebo response limit the potential to demonstrate worthwhile efficacy of a new intervention. This mini-review was motivated by the work of Bosman and colleagues(Neurogastroenterol Motil, 2022, and e14474) that is published in this issue of the journal in which they report on a systematic review and meta-analysis of placebo response in functional dyspepsia clinical trials. The review sets the scene for their work by putting it in the context of other disorders of brain-gut interaction and extra-gastrointestinal disorders. The review canvasses potential mechanisms of placebo response.

The Effects of Expectations and Worries on the Experience of COVID-19 Symptoms

Introduction

The COVID-19 pandemic has been shown to have profound effects on both mental and physical health. Distress and widespread uncertainty about global events and personal risk are associated with increased worry and negative expectations that impact physical health. Thus, the current pandemic poses a possibility for the experience of nocebo effects.

Objective

To evaluate the likelihood of nocebo-induced COVID-19 symptoms in a US sample.

Methods

An online study on the mental health impact of COVID-19 asked participants to complete a set of biweekly surveys over a 6-month period between April 2020 and May 2021. We focus on responses from 3,027 individuals who reported never testing positive for COVID-19. We assessed the association between two types of worry and self-reported symptoms of COVID-19. We used multi-level models to examine variations across and within participants over time. We further investigated the effects of pre-existing health conditions and mental health status.

Results

There was a positive association between symptoms and both general (b= 2.56, p<0.01) and personal worry (b=2.77, p<0.01). However, worry reported at one timepoint was not specifically associated with symptoms reported two weeks later (p = 0.63, p=0.56). We also found that a greater number of prior clinical comorbidities and greater mental health burden were significant predictors of symptom reporting.

Conclusions

These results suggest that increased worries during the COVID-19 pandemic were associated with greater symptoms. Further studies investigating worry and symptoms in populations with confirmed negative COVID-19 tests or isolated populations will be needed to isolate the occurrence of true nocebo effects during the pandemic.

[Placebo effects in analgesia : Influence of expectations on the efficacy and tolerability of analgesic treatment]

Expectations of patients influence the perception and neuronal processing of acute and chronic pain and modulate the effectiveness of analgesic treatment. The expectation of treatment is not only the most important determinant of placebo analgesia. Expectations of treatment also influence the efficacy and tolerability of "active" pharmacological and non-pharmacological treatment of pain. Recent insights into the psychological and neurobiological mechanisms underlying the clinically relevant effects of treatment expectations enable and call for the systematic integration and modulation of treatment expectations into analgesic treatment concepts. Such a strategy promises to optimize analgesic treatment and to prevent or reduce the burden of unwanted side effects and the misuse of analgesics, particularly of opioids. This review highlights the current concepts, recent achievements and also challenges and key open research questions.

Psychological mechanisms of offset analgesia: The effect of expectancy manipulation

A frequently used paradigm to quantify endogenous pain modulation is offset analgesia, which is defined as a disproportionate large reduction in pain following a small decrease in a heat stimulus. The aim of this study was to determine whether suggestion influences the magnitude of offset analgesia in healthy participants. A total of 97 participants were randomized into three groups (hypoalgesic group, hyperalgesic group, control group). All participants received four heat stimuli (two constant trials and two offset trials) to the ventral, non-dominant forearm while they were asked to rate their perceived pain using a computerized visual analogue scale. In addition, electrodermal activity was measured during each heat stimulus. Participants in both intervention groups were given a visual and verbal suggestion about the expected pain response in an hypoalgesic and hyperalgesic manner. The control group received no suggestion. In all groups, significant offset analgesia was provoked, indicated by reduced pain ratings (p < 0.001) and enhanced electrodermal activity level (p < 0.01). A significant group difference in the magnitude of offset analgesia was found between the three groups (F[2,94] = 4.81, p < 0.05). Participants in the hyperalgesic group perceived significantly more pain than the hypoalgesic group (p = 0.031) and the control group (p < 0.05). However, the electrodermal activity data did not replicate this trend (p > 0.05). The results of this study indicate that suggestion can be effective to reduce but not increase endogenous pain modulation quantified by offset analgesia in healthy participants.

Mitochondrial reactivity following acute exposure to experimental pain testing in people with HIV and chronic pain

Background: Physical stressors can cause a physiological response that can contribute to an increase in mitochondrial dysfunction and Mitochondrial DNA damage (mtDNA damage). People living with HIV (PWH) are more likely to suffer from chronic pain and may be more susceptible to mitochondrial dysfunction following exposure to a stressor. We used Quantitative Sensory Testing (QST) as an acute painful stressor in order to investigate whether PWH with/without chronic pain show differential mitochondrial physiological responses. Methods: The current study included PWH with (n = 26), and without (n = 29), chronic pain. Participants completed a single session that lasted approximately 180 min, including QST. Blood was taken prior to and following the QST battery for assays measuring mtDNA damage, mtDNA copy number, and mtDNA damage-associated molecular pattern (DAMP) levels (i.e., ND1 and ND6). Results: We examined differences between those with and without pain on various indicators of mitochondrial reactivity following exposure to QST. However, only ND6 and mtDNA damage were shown to be statistically significant between pain groups. Conclusion: PWH with chronic pain showed greater mitochondrial reactivity to laboratory stressors. Consequently, PWH and chronic pain may be more susceptible to conditions in which mitochondrial damage/dysfunction play a central role, such as cognitive decline.

Placebo and nocebo effects: from observation to harnessing and clinical application

Placebo and nocebo effects are salubrious benefits and negative outcomes attributable to non-specific symbolic components. Leveraging advanced experimental and analytical approaches, recent studies have elucidated complicated neural mechanisms that may serve as a solid basis for harnessing the powerful self-healing and self-harming capacities and applying these findings to improve medical practice and minimize the unintended exacerbation of symptoms in medical practice. We review advances in employing psychosocial, pharmacological, and neuromodulation approaches to modulate/harness placebo and nocebo effects. While these approaches show promising potential, translating these research findings into clinical settings still requires careful methodological, technical, and ethical considerations.

Impact of Vaccine Hesitancy on Onset, Severity and Type of Self-reported Adverse Events: A French Cross-Sectional Survey

INTRODUCTION

Little is known about the impact of mandatory vaccination on people who are reluctant to be vaccinated, despite the potential importance in terms of public health policy.

OBJECTIVE

We aimed to explore the relationship between vaccine hesitancy and onset, severity and characteristics of self-reported adverse events.

METHODS

We used a cross-sectional online survey conducted in 2021 among a representative sample of the French population aged 18 years and older (n = 1593). All reported adverse events were analyzed and categorized by trained experts in drug safety and pharmacovigilance. Multivariate binomial regressions on the onset of self-reported adverse events, vaccine hesitancy categories and predefined responders' characteristics were performed.

RESULTS

Overall, 590 (37.0%) participants reported at least one adverse event, with 121 (20.5%) considered it to be severe. Proportions of reported adverse events, ranging from 18% (in non-reluctant responders) to 65% (in very reluctant responders), and their severity, ranging from 5% (non-reluctant responders) to 41% (very reluctant responders), depended highly on attitudes toward vaccination. The adverse events profile remained similar between groups. In the multivariate regression model, beyond attitude toward vaccination, younger age and female gender were significantly associated with higher reporting of vaccine adverse events.

CONCLUSIONS

Our results suggest that vaccine hesitancy could be a major driver of patient-reported vaccine-related adverse events and their perceived severity. In this context, vaccinators must pay special attention to reluctant patients and inform them on the possible nocebo nature of these adverse events so as to prevent them.

Are Nocebo Effects in Adulthood Linked to Prenatal Maternal Cortisol Levels?

Objective

Placebo-induced adverse events, or nocebo effects, occur when doctor-patient communication anticipates the onset of negative symptoms. They have been found to correlate with the anxiety-related activity of the hypothalamic-pituitary-adrenal system. Here we try to determine if prenatal hyperactivity of this system, as assessed through plasma cortisol, may influence nocebo effects in adulthood.

Method

We investigated the rate and magnitude of nocebo effects in 378 adults whose prenatal maternal plasma cortisol was measured during the first, second and third trimester of pregnancy. The healthy subjects underwent a nocebo oxygen challenge. This consisted of the inhalation of fake (placebo) oxygen and assessment of the following adverse events: headache, chest pain, abdominal pain, and cough. Plasma cortisol responses during the nocebo adverse events were also measured.

Results

41 out of 46 (89.1%) subjects who reported 3 adverse events, and 37 out of 37 (100%) subjects who reported 4 adverse events had prenatal maternal cortisol above normal levels. By contrast, only 10 out of 143 (7%) subjects who reported 0 adverse events showed prenatal maternal cortisol above the normal range. Moreover, whereas subjects who reported 3 and 4 adverse events showed a significant increase in plasma cortisol following the nocebo challenge, subjects who reported 0 adverse events showed no changes.

Conclusions

These findings emphasize the importance of the doctor-patient communication in perceiving symptoms like pain, and suggest that those subjects with high prenatal maternal cortisol may be more sensitive to the effects of a negative communication in adulthood.

Preventing adverse events of chemotherapy for gastrointestinal cancer by educating patients about the nocebo effect: a randomized-controlled trial

BACKGROUND

Adverse events of chemotherapy may be caused by pharmacodynamics or psychological factors such as negative expectations, which constitute nocebo effects. In a randomized controlled trial, we examined whether educating patients about the nocebo effect is efficacious in reducing the intensity of self-reported adverse events.

METHODS

In this proof-of-concept study, N = 100 outpatients (mean age: 60.2 years, 65% male, 54% UICC tumour stage IV) starting first-line, de novo chemotherapy for gastrointestinal cancers were randomized 1:1 to a nocebo education (n = 49) or an attention control group (n = 51). Our primary outcome was patient-rated intensity of four chemotherapy-specific and three non-specific adverse events (rated on 11-point Likert scales) at 10-days and 12-weeks after the first course of chemotherapy. Secondary outcomes included perceived control of adverse events and tendency to misattribute symptoms.

RESULTS

General linear models indicated that intensity of adverse events differed at 12-weeks after the first course of chemotherapy (mean difference: 4.04, 95% CI [0.72, 7.36], p = .02, d = 0.48), with lower levels in the nocebo education group. This was attributable to less non-specific adverse events (mean difference: 0.39, 95% CI [0.04, 0.73], p = .03, d = 0.44) and a trend towards less specific adverse events in the nocebo education group (mean difference: 0.36, 95% CI [- 0.02, 0.74], p = .07, d = 0.37). We found no difference in adverse events at 10-days follow-up, perceived control of adverse events, or tendency to misattribute non-specific symptoms to the chemotherapy.

CONCLUSIONS

This study provides first proof-of-concept evidence for the efficacy of a brief information session in preventing adverse events of chemotherapy. However, results regarding patient-reported outcomes cannot rule out response biases. Informing patients about the nocebo effect may be an innovative and clinically feasible intervention for reducing the burden of adverse events.

TRIAL REGISTRATION

Retrospectively registered on March 27, 2018 to the German Clinical Trial Register (ID: DRKS00009501).

Functional neurological disorder and placebo and nocebo effects: shared mechanisms

Functional neurological disorder (FND) is characterized by neurological symptoms that cannot be explained by a structural neurological cause. Among the different aetiological models that have been proposed for FND, of note is the Bayesian predictive coding model, which posits that perception relies on top-down cortical predictions (priors) to infer the source of incoming sensory information. This model can also apply to non-pathological experiences, such as placebo and nocebo effects, wherein sensory information is shaped by prior expectations and learning. To date, most studies of the relationship between placebo and nocebo effects and FND have focused on the use of placebos for diagnosis and treatment of FND. Here, we propose that this relationship might go beyond diagnosis and therapy. We develop a framework in which shared cognitive, personality and neuroanatomical factors justify the consideration of a deeper link between FND and placebo and nocebo effects. This new perspective might offer guidance for clarification of the pathogenesis of FND and for the identification of potential biomarkers and therapeutic targets.

Informed Consent for Placebo-Controlled Trials: Do Ethics and Science Conflict?

The use of a placebo has been considered the best method for controlling bias in a prospective randomized clinical trial and provides the most rigorous test of treatment efficacy for evaluating a medical therapy. Placebos commonly produce clinically important effects particularly in studies where the primary outcomes are subjective. Yet the potential beneficial or harmful effects of placebos are often not addressed in designing a clinical trial, calculating the sample size, seeking consent, or interpreting clinical trial results. In this manuscript, we use an actual study to indicate three approaches that might be considered in seeking informed consent for placebo-controlled trials, and we explore the fundamental ethical and scientific complexities involved with each.

Avoidance of nocebo effects by coincident naming of treatment benefits during the medical interview for informed consent—Evidence from dynamometry

Introduction

In the context of giving risk information for obtaining informed consent, it is not easy to comply with the ethical principle of “primum nihil nocere.” Carelessness, ignorance of nocebo effects and a misunderstood striving for legal certainty can lead doctors to comprehensive and brutal risk information. It is known that talking about risks and side effects can even trigger those and result in distress and nonadherence to medication or therapy.

Methods

Recently, we have reported on significant clinically relevant effects of verbal and non-verbal suggestions on maximal muscular arm strength in healthy volunteers and in patients at two time points before surgery. Maximal strength during arm abduction was measured by dynamometry of the deltoid muscle group. Suggestions from clinical everyday life were formulated as presumed negative and neutral versions.

Results

Here, we report on the effects of two versions of risk information in 45 patients. After sole mentioning risks of a puncture for the placement of a pain catheter, the maximal arm muscle strength was significantly reduced to 83% of baseline several days (T1), and to 84% the evening before surgery (T2). Strength was not significantly decreased and close to baseline at T1 and T2 when risks and benefits of a pain catheter were combined in one sentence. The difference between both versions was significant. With persistent normal distribution of values, the effect was due to uniform reactions of many patients, not to strong reactions of a few. High suggestibility and increase of anxiety with approaching surgery were identified as influencing factors for the neutralizing effect of modified wording.

Conclusion

We not only suggest an alternative formulation for risk information to avoid nocebo effects but present an objective method to quantify and compare effects of different wordings. Thereby, we provide evidence that concurrently given positive aspects can neutralize negative effects during medical interview.

Placebo administration for dry eye disease: a level I evidence based systematic review and meta-analysis

Background

The efficacy of various common treatment options for dry eye disease (DED) has been investigated against placebo. However, the potential beneficial effect of placebo in the management of DED is still unclear.

Aim

This meta-analysis investigated the impact of placebo administration in DED in Ocular Surface Disease Index (OSDI), Schirmer I test (SIT), tear breakup time (TBUT), corneal staining, and complications.

Method

This meta-analysis and systematic review was conducted according to the 2020 PRISMA guidelines. In March 2022, Pubmed, Web of Science, Google Scholar, and Embase were accessed. All the randomised clinical trials which investigated any active treatment against a placebo control group were considered. The following data were extracted at baseline and at last follow-up: Ocular Surface Disease Index (OSDI), tear breakup time test (TBUT), Schirmer I test (SIT), corneal staining.

Results

Data from 56 studies (12,205 patients) were retrieved. Placebo administration is not effective in improving TBUT (P = 0.3), OSDI (P = 0.2), SIT (P = 0.1) and corneal staining (P = 0.1) from baseline to last follow-up. Active treatment led to a higher TBUT and SIT compared to placebo administration (P < 0.0001). The active treatment resulted in a lower OSDI compared to placebo administration (P = 0.0005). Five studies reported data on the corneal staining. No difference was found between placebo administration and active treatment (P = 0.8).

Conclusion

Placebo administration does not impact symptoms of DED and can be successfully employed to evaluate the efficacy of active treatments.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11096-022-01439-y.

Less stress, better success: a scoping review on the effects of anxiety on anesthetic and analgesic consumption

Preoperative anxiety has an incidence of 11-80% in patients undergoing surgical or interventional procedures. Understanding the role of preoperative anxiety on intraoperative anesthetic requirements and postoperative analgesic consumption would allow personalized anesthesia care. Over- or under-anesthetizing patients can lead to complications such as postoperative cognitive dysfunction in elderly patients, or procedural discomfort, respectively. Our scoping review focuses on the current evidence regarding the association between preoperative anxiety and intraoperative anesthetic and/or postoperative analgesic consumption in patients undergoing elective surgical or interventional procedures. Based on 44 studies that met the inclusion criteria, we found that preoperative anxiety has a significant positive correlation effect on intraoperative propofol and postoperative opioid consumption. The analysis of the literature is limited by the heterogeneity of preoperative anxiety tools used, study designs, data analyses, and outcomes. The use of shorter, validated preoperative anxiety assessment tools may help optimize the intraoperative anesthetic and postoperative analgesic regimen. Further research to determine the most feasible and clinically relevant preoperative anxiety tool and subsequent implementation has the potential to optimize perioperative care and improve patient outcomes.

Action-Shapers and Their Neuro-Immunological Foundations

Not all our intentions translate into actions, as our capacity to act may be influenced by a variety of mental and biochemical factors. In this article, we present a comprehensive account of how neuro-immunological processes affect our intentional abilities and our capacity to act. We do so by extending the theory of thought-shapers (TTS) through the notion of action-shapers and combining this theory with the essential embodiment thesis (EE). This thesis about the mind-body relation says that human minds are necessarily and completely embodied. Action-shapers dynamically constitute the action-space of individuals, affecting their capacity to take action or to select one course of action over another. We highlight the effects and interactions of neuro-immunological effective processes in the body to demonstrate how they shape the action-space. In this article, we consider neuro-immunological effective processes that influence the gut-brain axis, chronic stress, high levels of sugar intake, the amygdala and the effects of prolonged stress. We investigate the effects of these processes on the perception and on the capacity to form intentions and act on them. We conclude the paper by providing a concise account of action-shapers, in which we attempt to summarize the line of argumentation and provide suggestions for further research.

Rostral Anterior Cingulate Cortex–Ventrolateral Periaqueductal Gray Circuit Underlies Electroacupuncture to Alleviate Hyperalgesia but Not Anxiety-Like Behaviors in Mice With Spared Nerve Injury

Neuropathic pain is a common cause of chronic pain and is often accompanied by negative emotions, making it complex and difficult to treat. However, the neural circuit mechanisms underlying these symptoms remain unclear. Herein, we present a novel pathway associated with comorbid chronic pain and anxiety. Using chemogenetic methods, we found that activation of glutamatergic projections from the rostral anterior cingulate cortex (rACC^Glu) to the ventrolateral periaqueductal gray (vlPAG) induced both hyperalgesia and anxiety-like behaviors in sham mice. Inhibition of the rACC^Glu-vlPAG pathway reduced anxiety-like behaviors and hyperalgesia in the spared nerve injury (SNI) mice model; moreover, electroacupuncture (EA) effectively alleviated these symptoms. Investigation of the related mechanisms revealed that the chemogenetic activation of the rACC^Glu-vlPAG circuit effectively blocked the analgesic effect of EA in the SNI mice model but did not affect the chronic pain-induced negative emotions. This study revealed a novel pathway, the rACC^Glu-vlPAG pathway, that mediates neuropathic pain and pain-induced anxiety.

What Do Placebo and Nocebo Effects Have to Do With Health Equity? The Hidden Toll of Nocebo Effects on Racial and Ethnic Minority Patients in Clinical Care

A placebo effect is a positive clinical response to non-specific elements of treatment with a sham or inert replica of a drug, device, or surgical intervention. There is considerable evidence that placebo effects are driven by expectation of benefit from the intervention. Expectation is shaped by a patient's past experience, observations of the experience of others, and written, verbal, or non-verbal information communicated during treatment. Not surprisingly, expectation in the clinical setting is strongly influenced by the attitude, affect, and communication style of the healthcare provider. While positive expectations can produce beneficial effects, negative information and experiences can lead to negative expectations, and consequently negative or nocebo effects. Key components identified and studied in the placebo and nocebo literature intersect with factors identified as barriers to quality care in the clinical setting for Black patients and other patients of color, including poor patient-clinician communication, medical mistrust, and perceived discrimination. Thus, in the context of discrimination and bias, the absence of placebo and presence of nocebo-generating influences in clinical settings could potentially reinforce racial and ethnic inequities in clinical outcomes and care. Healthcare inequities have consequences that ripple through the medical system, strengthening adverse short- and long-term outcomes. Here, we examine the potential for the presence of nocebo effects and absence of placebo effects to play a role in contributing to negative outcomes related to unequal treatment in the clinical encounter.

Frequency of Adverse Events in the Placebo Arms of COVID-19 Vaccine Trials: A Systematic Review and Meta-analysis

Importance

Adverse events (AEs) after placebo treatment are common in randomized clinical drug trials. Systematic evidence regarding these nocebo responses in vaccine trials is important for COVID-19 vaccination worldwide especially because concern about AEs is reported to be a reason for vaccination hesitancy.

Objective

To compare the frequencies of AEs reported in the placebo groups of COVID-19 vaccine trials with those reported in the vaccine groups.

Data Sources

For this systematic review and meta-analysis, the Medline (PubMed) and Cochrane Central Register of Controlled Trials (CENTRAL) databases were searched systematically using medical subheading terms and free-text keywords for trials of COVID-19 vaccines published up to July 14, 2021.

Study Selection

Randomized clinical trials of COVID-19 vaccines that investigated adults aged 16 years or older were selected if they assessed solicited AEs within 7 days of injection, included an inert placebo arm, and provided AE reports for both the vaccine and placebo groups separately. Full texts were reviewed for eligibility by 2 independent reviewers.

Data Extraction and Synthesis

Data extraction and quality assessment were performed independently by 2 reviewers, adhering to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guideline and using the Cochrane risk-of-bias tool. Meta-analyses were based on random-effects models.

Main Outcomes and Measures

The primary outcomes were the proportions of placebo recipients reporting overall, systemic, and local (injection-site) AEs as well as logarithmic odds ratios (ORs) to evaluate group differences. Outcomes were tested for significance using z tests with 95% CIs.

Results

Twelve articles with AE reports for 45 380 participants (22 578 placebo recipients and 22 802 vaccine recipients) were analyzed. After the first dose, 35.2% (95% CI, 26.7%-43.7%) of placebo recipients experienced systemic AEs, with headache (19.3%; 95% CI, 13.6%-25.1%) and fatigue (16.7%; 95% CI, 9.8%-23.6%) being most common. After the second dose, 31.8% (95% CI, 28.7%-35.0%) of placebo recipients reported systemic AEs. The ratio between placebo and vaccine arms showed that nocebo responses accounted for 76.0% of systemic AEs after the first COVID-19 vaccine dose and for 51.8% after the second dose. Significantly more vaccine recipients reported AEs, but the group difference for systemic AEs was small after the first dose (OR, -0.47; 95% CI, -0.54 to -0.40; P < .001; standardized mean difference, -0.26; 95% CI, -0.30 to -0.22) and large after the second dose (OR, -1.36; 95% CI, -1.86 to -0.86; P < .001; standardized mean difference, -0.75; 95% CI, -1.03 to -0.47).

Conclusions and Relevance

In this systematic review and meta-analysis, significantly more AEs were reported in vaccine groups compared with placebo groups, but the rates of reported AEs in the placebo arms were still substantial. Public vaccination programs should consider these high rates of AEs in placebo arms.

Characteristics, mechanism, and management of pain in atopic dermatitis: A literature review

BACKGROUND

Atopic dermatitis (AD) is a chronic, pruritic, immune-mediated inflammatory disease. Developments in basic science and clinical research have increased our understanding of AD. Although pain as a symptom of AD is underemphasized in previous studies, multiple researchers address pain as a frequent burden of AD. However, the exact role of pain in AD is not fully understood.

AIMS

Our review aimed to summarize the current evidence focusing on characteristics, mechanism, and management of pain in AD.

MATERIALS & METHODS

We conducted a thorough literature review in the PubMed database to figure out different aspects discussing pain in AD, including pain symptoms, burden, the relationship between pain and itch, mechanism, and pain management in AD.

RESULTS AND CONCLUSION

AD patients affected by skin pain vary from 42.7%-92.2% with remarkable intensity and heavy burden. Skin pain and itch interacted both in symptoms and mechanisms. Atopic skin with the impaired barrier, neurogenic inflammation mediators, peripheral and central sensitization of pain may possibly explain pain mechanism in AD. Future research is needed to clarify the commonality and disparity of pain and itch in AD in order to seek efficacious medications and treatment.

Spinal CCK contributes to somatic hyperalgesia induced by orofacial inflammation combined with stress in adult female rats

In some chronic primary pain conditions such as temporomandibular disorder (TMD) and fibromyalgia syndrome (FMS), mild or chronic stress enhances pain. TMD and FMS often occur together, but the underlying mechanisms are unclear. The purpose of this study was to investigate the role of cholecystokinin (CCK) in the spinal cord in somatic hyperalgesia induced by orofacial inflammation combined with stress. Somatic hyperalgesia was detected by the thermal withdrawal latency and mechanical withdrawal threshold. The expression of CCK₁ receptors, CCK₂ receptors, ERK1/2 and p-ERK1/2 in the spinal cord was examined by Western blot. After the stimulation of orofacial inflammation combined with 3 day forced swim, the expression of CCK₂ receptors and p-ERK1/2 protein in the L4-L5 spinal dorsal horn increased significantly, while the expression of CCK₁ receptors and ERK1/2 protein remained unchanged. Intrathecal injection of the CCK₂ receptor antagonist YM-022 or mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor PD98059 blocked somatic hyperalgesia induced by orofacial inflammation combined with stress. Intrathecal administration of the MEK inhibitor blocked somatic sensitization caused by the CCK receptor agonist CCK8. The CCK₂ receptor antagonist YM-022 significantly reduced the expression of p-ERK1/2. These data indicate that upregulation of CCK₂ receptors through the MAPK pathway contributes to somatic hyperalgesia in this comorbid pain model. Thus, CCK₂ receptors and MAPK pathway may be potential targets for the treatment of TMD comorbid with FMS.

A social affective neuroscience lens on placebo analgesia

Pain is a fundamental experience that promotes survival. In humans, pain stands at the intersection of multiple health crises: chronic pain, the opioid epidemic, and health disparities. The study of placebo analgesia highlights how social, cognitive, and affective processes can directly shape pain, and identifies potential paths for mitigating these crises. This review examines recent progress in the study of placebo analgesia through affective science. It focuses on how placebo effects are shaped by expectations, affect, and the social context surrounding treatment, and discusses neurobiological mechanisms of placebo, highlighting unanswered questions and implications for health. Collaborations between clinicians and social and affective scientists can address outstanding questions and leverage placebo to reduce pain and improve human health.