Effects of sex on placebo effects in chronic pain participants: a cross-sectional study

Do patients with fibromyalgia syndrome and healthy people differ in their opinions on placebo effects in routine medical care?

OBJECTIVES

Placebo effects can relieve acute and chronic pain in both research and clinical treatments by learning mechanisms. However, the application of placebo-based treatment strategies in routine medical care is questioned. The current study investigated the opinions of patients with fibromyalgia and healthy controls regarding learning of placebo effects and their practical applications.

METHOD

An online survey asked 158 age- and sex-matched adult patients and controls (79 per group) to rate the perceived influence of various placebo learning mechanisms on pain relief, and the acceptability and perceived effectiveness of placebo-based strategies (open-label, closed-label, dose-extending, and treatment-enhancing strategies). Respondents' knowledge about placebo effects was obtained through a 7-item quiz.

RESULTS

The groups did not differ in the perceived influence of placebo learning mechanisms on pain relief (p = 0.217). Controls considered closed-label and treatment-enhancing strategies more acceptable than patients (p = 0.003 and p < 0.001), whereas controls perceived all strategies more effective. In both groups, closed-label strategies were significantly less acceptable than any other strategy (p-values < 0.001), and treatment-enhancing or dose-extending strategies were most acceptable. Higher acceptability was predicted by higher perceived effectiveness ratings (p < 0.001). Also, increased placebo knowledge was related to higher acceptability (p = 0.03) and perceived effectiveness (p < 0.001).

DISCUSSION

This survey suggests that both the medical history of patients and knowledge about placebo effects affect the acceptability and perceived effectiveness of placebo-based strategies. Furthermore, strategies that are transparent, assumed effective, or combined with existing medical treatments are deemed most acceptable. Keeping these factors in mind is essential for the clinical implementation of placebo-based strategies in routine medical care.

The effects of socioeconomic position on endogenous pain modulation: A quasi-experimental approach

Socioeconomic Position (SEP) is a multidimensional construct encompassing education, income, occupation, and neighborhood distress, influencing chronic pain severity, interference, and duration. However, its impact on placebo analgesia, where reduced pain perception occurs due to treatment belief, remains understudied. Using a quasi-experimental approach, we investigated SEP's influence on placebo analgesia in 401 participants with temporomandibular disorder (TMD) and 400 pain-free individuals. Using latent class analysis, we grouped participants into two SEP groups based on self-reported education, income, occupation, and neighborhood distress indices, including the area deprivation and distressed community indexes. Ancestry Informative Markers (AIMs) and self-reported race were included to account for genetic and demographic influences. Placebo analgesia was elicited using verbal suggestion and classical conditioning. Linear mixed models were employed to analyze SEP's impact, while multiple regression and ANCOVA assessed AIMs' and race's effects. Comparable placebo effects were observed between participants with TMD and pain-free individuals (F(1,4765.73) = 0.49, p = 0.48). A trend was noted in the main effect of SEP (F(1,4764.5) = 3.64, p = 0.056). Among TMD participants, those with distressed SEP exhibited lower placebo analgesia (F(1,4765.73) = 7.9, p = 0.005), while placebo response did not differ by SEP in pain-free participants (F(1,4765.73) = 0.27, p = 0.59). East Asian ancestry (β = 5.71, 95% CI [1.50, 9.92]) and self-reported Asian (mean = 24.20, sem = 1.52, p = 0.020) were associated with greater placebo analgesia. This study highlights the interplay of SEP, AIMs, and race in placebo analgesia and calls for tailored pain management interventions. PERSPECTIVE: SEP significantly contributes to pain disparities. This quasi-experimental study demonstrates analogous placebo analgesia between chronic pain and pain-free individuals but finds lower placebo analgesia only among individuals with chronic pain and distressed SEP. This highlights a link between chronic pain, SEP, and impaired placebo effects, suggesting new avenues for research.

Remotely administered non-deceptive placebos reduce COVID-related stress, anxiety, and depression

Research suggests that placebos administered without deception (i.e. non-deceptive placebos) may provide an effective and low-effort intervention to manage stress and improve mental health. However, whether non-deceptive placebos administered remotely online can manage distress for people at risk for developing high levels of affective symptoms remains unclear. Volunteers experiencing prolonged stress from the COVID-19 pandemic were recruited into a randomized controlled trial to examine the efficacy of a non-deceptive placebo intervention administered remotely online on affective outcomes. COVID-related stress, overall stress, anxiety, and depression were assessed at baseline, midpoint, and endpoint. Compared with the control group, participants in the non-deceptive placebo group reported significant reductions from baseline in all primary affective outcomes after 2 weeks. Additionally, participants in the non-deceptive placebo group found the intervention feasible, acceptable, and appropriate for the context. Non-deceptive placebos, even when administered remotely online, offer an alternative and effective way to help people manage prolonged stress. Future large-scale studies are needed to determine if non-deceptive placebos can be effective across different prolonged stress situations and for clinical populations.

Placebo treatment affects brain systems related to affective and cognitive processes, but not nociceptive pain

Drug treatments for pain often do not outperform placebo, and a better understanding of placebo mechanisms is needed to improve treatment development and clinical practice. In a large-scale fMRI study (N = 392) with pre-registered analyses, we tested whether placebo analgesic treatment modulates nociceptive processes, and whether its effects generalize from conditioned to unconditioned pain modalities. Placebo treatment caused robust analgesia in conditioned thermal pain that generalized to unconditioned mechanical pain. However, placebo did not decrease pain-related fMRI activity in brain measures linked to nociceptive pain, including the Neurologic Pain Signature (NPS) and spinothalamic pathway regions, with strong support for null effects in Bayes Factor analyses. In addition, surprisingly, placebo increased activity in some spinothalamic regions for unconditioned mechanical pain. In contrast, placebo reduced activity in a neuromarker associated with higher-level contributions to pain, the Stimulus Intensity Independent Pain Signature (SIIPS), and affected activity in brain regions related to motivation and value, in both pain modalities. Individual differences in behavioral analgesia were correlated with neural changes in both modalities. Our results indicate that cognitive and affective processes primarily drive placebo analgesia, and show the potential of neuromarkers for separating treatment influences on nociception from influences on evaluative processes.

Sex Differences in the Serum Proteomic Profile During Acute Low Back Pain-A Preliminary Study of the Relationship to Future Low Back Pain

The molecular processes driving the transition from acute to chronic low back pain (LBP) remain poorly understood and are likely to be sexually dimorphic. This study aimed to explore sex differences in the serum proteomic profile of people experiencing an acute LBP episode and determine if serum protein concentrations were associated with three-month outcome. Serum samples were collected through venepuncture from 30 female and 29 male participants experiencing an acute LBP episode. Serum samples underwent trypsin digestion and fractionation using hydrophobic interaction chromatography and were then analysed using mass-spectrometry. Mass-spectrometry spectra were searched in the Swissprot database for protein identification. Sex differences in protein abundance changes were evident upon inspection of fold changes. Multivariable data analysis identified 21 serum proteins during the acute episode that correctly classified 93% of males and 23 serum proteins that correctly classified 90% of females with ongoing LBP at 3 months. Pathway analysis suggested the differentially expressed proteins during acute LBP were frequently involved in immune, inflammatory, complement, or coagulation responses. This data provides preliminary evidence that biological processes during an acute LBP episode may contribute to the resolution, or persistence, of LBP symptoms at 3 months, however, these processes differ between males and females. PERSPECTIVE: Differential expression of serum proteins was observed between male and female participants during an acute LBP episode. This preliminary work provides a foundation for future research targeting distinct immune system processes in males and females that may interfere with the transition from acute to chronic LBP.

A developmental framework for understanding the influence of sex and gender on health: Pediatric pain as an exemplar

Sex differences are a robust finding in many areas of adult health, including cardiovascular disease, psychiatric disorders, and chronic pain. However, many sex differences are not consistently observed until after the onset of puberty. This has led to the hypothesis that hormones are primary contributors to sex differences in health outcomes, largely ignoring the relative contributions of early developmental influences, emerging psychosocial factors, gender, and the interaction between these variables. In this paper, we argue that a comprehensive understanding of sex and gender contributions to health outcomes should start as early as conception and take an iterative biopsychosocial-developmental perspective that considers intersecting social positions. We present a conceptual framework, informed by a review of the literature in basic, clinical, and social science that captures how critical developmental stages for both sex and gender can affect children's health and longer-term outcomes. The literature on pediatric chronic pain is used as a worked example of how the framework can be applied to understanding different chronic conditions.

Clinical Phenotypes Supporting the Relationship Between Sleep Disturbance and Impairment of Placebo Effects

Lack of good sleep or insomnia can lead to many health issues, including an elevated risk of cardiovascular disease, obesity, fatigue, low mood, and pain. While chronic pain negatively impacts sleep quality, the relationship between descending pain modulatory systems like placebo effects and sleep quality is not thoroughly known. We addressed this aspect in a cross-sectional study in participants with chronic pain. Placebo effects were elicited in a laboratory setting using thermal heat stimulations delivered with visual cues using classical conditioning and verbal suggestions. We estimated the levels of insomnia severity with the Insomnia Severity Index and the sleep quality with the Pittsburg Sleep Quality Index. The previous night's sleep continuity was assessed as total sleep time, sleep efficiency, and sleep midpoint the night before the experiment. 277 people with chronic pain and 189 pain-free control individuals participated. Participants with chronic pain and insomnia showed smaller placebo effects than those with chronic pain without insomnia. Similarly, poor sleep quality was associated with reduced placebo effects among participants with chronic pain. Clinical anxiety measured by Depression Anxiety Stress Scales partially mediated these effects. In contrast, placebo effects were not influenced by the presence of insomnia or poor sleep quality in pain-free participants. Sleep continuity the night before the experiment did not influence the placebo effects. Our results indicate that participants who experience insomnia and/or poor sleep quality and chronic pain have smaller placebo effects, and that the previous night sleep continuity does not influence the magnitude of placebo effects. PERSPECTIVE: This study examined the relationship between sleep disturbances and experimentally induced placebo effects. We found that individuals with chronic pain who experience insomnia and poor sleep quality demonstrated reduced placebo effects compared to their counterparts with good sleep quality and no insomnia.

Mapping expectancy-based appetitive placebo effects onto the brain in women

Suggestions about hunger can generate placebo effects on hunger experiences. But, the underlying neurocognitive mechanisms are unknown. Here, we show in 255 women that hunger expectancies, induced by suggestion-based placebo interventions, determine hunger sensations and economic food choices. Functional magnetic resonance imaging in a subgroup (n = 57/255) provides evidence that the strength of expecting the placebo to decrease hunger moderates medial prefrontal cortex activation at the time of food choice and attenuates ventromedial prefrontal cortex (vmPFC) responses to food value. Dorsolateral prefrontal cortex activation linked to interference resolution formally mediates the suggestion-based placebo effects on hunger. A drift-diffusion model characterizes this effect by showing that the hunger suggestions bias participants' food choices and how much they weigh tastiness against the healthiness of food, which further moderates vmPFC-dlPFC psychophysiological interactions when participants expect decreased hunger. Thus, suggestion-induced beliefs about hunger shape hunger addressing economic choices through cognitive regulation of value computation within the prefrontal cortex.

Understanding Placebo and Nocebo Responses Based on a Randomized Sham-Controlled Study on Acupuncture in Integrative Cancer Care

Objective: Since placebo and nocebo-responses during acupuncture therapy are rarely studied in clinical contexts, the objective was to investigate placebo and nocebo-responses in a clinical context through comparing positive and negative side-effects between genuine and sham acupuncture, and to identify factors modifying placebo and nocebo-responses. Methods: Patients reported positive side-effects (non-intended positive effects) or negative side-effects (non-intended negative effects) of genuine (penetrating; n = 109) or sham (telescopic non-penetrating; n = 106) acupuncture during 5 weeks of chemoradiation for cancer. Results: The genuine and the sham acupuncture group reported rather similar frequencies of positive (P-values .223-.800) or negative (P-values .072-1.0) side-effects: relaxation 59%/57% of the patients, improved mood 46%/38%, improved sleep 38%/38%, pain-reduction 36%/28%, tiredness 42%/42%, feeling cold 37%/31%, sweating 23%/21%, and dizziness 20%/12%. Positive side-effects occurred in 79% of patients who highly believed acupuncture to be effective, compared to in 0% of patients who did not believe. Other factors associated with placebo-response were female sex (P = .042), anxious mood (P = .007), depressed mood (P = .018), and blinding-success (P = .033). Factors associated with nocebo response were female sex (P = .049), younger age (P = .010), and needle-induced pain (P = .014). Sham-treated patients experiencing positive side-effects experienced better quality of life at the end of the treatment period (mean, m 64 on a scale 0-100 millimetres, Standard Deviation, SD, ±26.1 mm) than those who did not (m 48 ± 25.5 mm), P = .048 (adjusted for other characteristics). Conclusions: Clinically significant levels of placebo and nocebo effects commonly occurred during acupuncture therapy in integrative cancer care and this paper identified factors modifying these responses. This implicates that acupuncture-delivering therapists striving to maximize placebo-responses and minimize nocebo-responses may considering strengthen the patient's treatment expectations, and offer a pleasant, pain-free, acupuncture treatment.

Placebo effects in osteoarthritis: implications for treatment and drug development

Osteoarthritis (OA) is the most common form of arthritis worldwide, affecting ~500 million people, yet there are no effective treatments to halt its progression. Without any structure-modifying agents, management of OA focuses on ameliorating pain and improving function. Treatment approaches typically have modest efficacy, and many patients have contraindications to recommended pharmacological treatments. Drug development for OA is hindered by the gradual and progressive nature of the disease and the targeting of established disease in clinical trials. Additionally, new medications for OA cannot receive regulatory approval without demonstrating improvements in both structure (pathological features of OA) and symptoms (reduced pain and/or improved function). In clinical trials, people with OA show high 'placebo responses', which hamper the ability to identify new effective treatments. Placebo responses refer to the individual variability in response to placebos given in the context of clinical trials and other settings. Placebo effects refer specifically to short-lasting improvements in symptoms that occur because of physiological changes. To mitigate the effects of the placebo phenomenon, we must first understand what it is, how it manifests, how to identify placebo responders in OA trials and how these insights can be used to improve clinical trials in OA. Leveraging placebo responses and effects in clinical practice might provide additional avenues to augment symptom management of OA.

Individual Dimensions of Pain Catastrophizing Do Not Mediate the Effect of Sociodemographic and Psychological Factors on Chronic Orofacial Pain Severity, Interference, and Jaw Limitation: A Structural Equation Modeling Approach

Pain catastrophization (PC), involving rumination, magnification, and helplessness, can be viewed as a coping strategy associated with chronic pain. PC is considered a driving force in mediating pain-related outcomes, but it is still unclear whether PC mediates the relationship between psychological and sociodemographic factors with chronic pain when considered in a single model. Using baseline data from a parent study, this study examined the effect of positive and negative psychological and sociodemographic factors on pain severity, interference, and jaw limitation mediated by the PC dimensions in a sample of 397 temporomandibular disorder (TMD) participants using structural equation modeling (SEM). SEM revealed that pain severity regressed on age, sex, education, and income; interference regressed on positive and negative psychological factors, education, and income; and jaw limitation regressed on age. The PC dimensions did not individually mediate these relationships. Although they jointly mediated the relationships between negative psychological factors and pain severity and between age and pain interference, the effect size was small, suggesting that PC is not a critical factor in mediating TMD pain outcomes. Reducing negative cognitions, not just PC, may be of greatest benefit to the most vulnerable TMD populations. PERSPECTIVE: This study examines sociodemographic and psychological factors that affect orofacial pain, finding that the pain catastrophizing dimensions do not mediate these relationships. Understanding which factors most strongly affect pain outcomes will help identify targets for intervention to produce the greatest benefit for the most vulnerable persons suffering from pain.

Yoga and massage are associated with small experimental placebo effects in chronic orofacial pain

BACKGROUND

Complementary and Integrative Health Approaches (CIHA), including but not limited to, natural products and Mind and Body Practices (MBPs), are promising non-pharmacological adjuvants to the arsenal of pain management therapeutics. We aim to establish possible relationships between use of CIHA and the capacity of descending pain modulatory system in the form of occurrence and magnitude of placebo effects in a laboratory setting.

METHODS

This cross-sectional study investigated the relationship between self-reported use of CIHA, pain disability, and experimentally induced placebo hypoalgesia in chronic pain participants suffering from Temporomandibular Disorders (TMD). In the 361 enrolled TMD participants, placebo hypoalgesia was measured using a well-established paradigm with verbal suggestions and conditioning cues paired with distinct heat painful stimulations. Pain disability was measured with the Graded Chronic Pain Scale, and use of CIHA were recorded with a checklist as part of the medical history.

RESULTS

Use of physically oriented MBPs (e.g., yoga and massage) was associated with reduced placebo effects (F1,2110.44  = 23.15, p < 0.001, Cohen's d = 0.171). Further, linear regressions indicated that greater number of physically oriented MBPs predicted smaller placebo effects (β = -0.17, p = 0.002), and less likelihood of being a placebo responder (OR = 0.70, p = 0.004). Use of psychologically oriented MBPs and natural product were not associated with placebo effects magnitude and responsiveness.

CONCLUSIONS

Our findings suggest that use of physically oriented CIHA was associated with experimental placebo effects possibly through an optimized capability to recognize distinct somatosensorial stimulations. Future research is needed to understand the mechanisms underlying placebo-induced pain modulation in CIHA users.

SIGNIFICANCE

Chronic pain participants who use physically oriented mind-body practices, such as yoga and massage, demonstrated attenuated experimentally induced placebo hypoalgesia in comparison with those who do not use them. This finding disentangled the relationship between use of complementary and integrative approaches and placebo effects, providing the potential therapeutic perspective of endogenous pain modulation in chronic pain management.

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.

Predicting Treatment Responses in Patients With Osteoarthritis: Results From Two Phase III Tanezumab Randomized Clinical Trials

Prediction of treatment responses is essential to move forward translational science. Our question was to identify patient-based variables that predicted responses to treatments. We conducted secondary analyses on pooled data from two randomized phase III clinical trials (NCT02697773 and NCT02709486) conducted in participants with moderate to severe osteoarthritis randomized to subcutaneous placebo (n = 514) or tanezumab 2.5 mg (n = 514). We used gradient boosted regression trees to identify variables that predicted Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) Pain subscale scores at Week 16 and marginal plots to determine the directional relationship between each variable category and responses to placebo or tanezumab within the models. We also used Virtual Twins models to identify potential subgroups of response to the active treatment vs. placebo. We found that responses to placebo were predicted by baseline WOMAC Physical Function, baseline WOMAC Pain, the radiographic classification of the index joint, and the standard deviation of diary pain scores at baseline. In contrast, baseline WOMAC Pain along with failure of prior medications, duration of disease, and standard deviation of diary pain scores at baseline were predictive of tanezumab responses as expressed by the WOMAC Pain scores at Week 16. Those who responded to tanezumab vs. placebo were identified based on the radiographic classification of the index joint and either age or smoking status. These secondary-data analyses identified distinct and common patient-based variables to predict response to placebo or tanezumab. These findings will inform the design of future clinical trials, helping to move forward clinical pharmacology and translational science.

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.

The neglect of sex: A call to action for including sex as a biological variable in placebo and nocebo research

Sex differences exist in the prevalence, progression and treatment efficacy of a wide array of medical conditions. While the placebo and nocebo effects have become increasingly relevant in the clinical arena, little is known about the influence of biological sex on placebo and nocebo effects. This paper discusses the existing, relatively limited and sometimes conflicting evidence about how sex impacts the occurrence and magnitude of the placebo and nocebo effects, mainly focusing on pain studies. We present recent evidence that when compared to men, women suffering from chronic orofacial pain may derive greater benefit from the placebo effect for analgesia. Nonetheless, we broadly argue that the field is not currently positioned to draw definitive conclusions and propose several important factors that may explain the inconsistency in the literature and that should be taken into account in future research. These include the specific target symptom of the placebo or nocebo manipulation and whether or not the target is related to the medical condition, the placebo or nocebo induction method, the sex of the experimenter or physician, and so forth. Future research should intentionally include sex a biological variable to favor translation of placebo and nocebo mechanisms into clinical applications.

Quantitative Sensory Testing Across Chronic Pain Conditions and Use in Special Populations

Chronic pain imposes a significant burden to the healthcare system and adversely affects patients' quality of life. Traditional subjective assessments, however, do not adequately capture the complex phenomenon of pain, which is influenced by a multitude of factors including environmental, developmental, genetic, and psychological. Quantitative sensory testing (QST), established as a protocol to examine thermal and mechanical sensory function, offers insight on potential mechanisms contributing to an individual's experience of pain, by assessing their perceived response to standardized delivery of stimuli. Although the use of QST as a research methodology has been described in the literature in reference to specific pain populations, this manuscript details application of QST across a variety of chronic pain conditions. Specific conditions include lower extremity chronic pain, knee osteoarthritis, chronic low back pain, temporomandibular joint disorder, and irritable bowel syndrome. Furthermore, we describe the use of QST in placebo/nocebo research, and discuss the use of QST in vulnerable populations such as those with dementia. We illustrate how the evaluation of peripheral sensory nerve function holds clinical promise in targeting interventions, and how using QST can enhance patient education regarding prognostic outcomes with particular treatments. Incorporation of QST methodology in research investigations may facilitate the identification of common mechanisms underlying chronic pain conditions, guide the development of non-pharmacological behavioral interventions to reduce pain and pain-related morbidity, and enhance our efforts toward reducing the burden of chronic pain.

Placebo Effects on Stress, but Not on Pain Reports. A Multi-Experiment Study

Background

Contextual factors, such as participant/experimenter sex may moderate the placebo effects. We tested whether the participant and experimenter sex modulated placebo effects on experimentally induced pain and associated stress.

Objective

To investigate if (i) participant sex and (ii) experimenter sex influence placebo analgesia and subjective and physiological stress in two experiments employing a within-subjects and a mixed design, respectively. Placebo effects were investigated in pain reports, stress, and blood pressure.

Methods

Participants received painful stimulations and a placebo cream. In Experiment One (N = 59) participants underwent a placebo condition (PC) and a natural history condition (NHC) in random order. A placebo cream was applied in the PC and then the heat stimulation temperature was surreptitiously lowered. Identical stimulations were administered in the NHC, but with no cream, no information, and no lowered temperature. In Experiment Two, participants (N = 93) were randomly assigned to three groups receiving either a placebo cream with surreptitiously lowered intensity of electric stimuli (Placebo, PG), a placebo cream (Cream-Control, CCG) without changing the stimuli, or lowered intensity, but with no cream (Pain-Control, PCG) in a mixed design. All participants in both experiments received the same stimuli in the post-test as in the pre-test. Four experimenters (two females) in Experiment One, and five experimenters (two females) in Experiment Two conducted the studies.

Results

No placebo effect was seen on pain. However, there were placebo effects on stress, moderated by participant and experimenter sex: in Experiment One males in the PC had lower diastolic blood pressure (DBP) compared to males in the NHC. Participants in the PC had lower DBP compared to the NHC when tested by a female. In Experiment Two, participants expected more cream effectiveness when a female experimenter administered it, and reported lower stress in the PG compared to the PCG when tested by females.

Conclusion

Our findings highlight a distinction between placebo effects on pain and on associated stress. Secondly, female experimenters recorded lower physiological and subjective stress, higher effectiveness expectations, and lower pain from both sexes compared to male experimenters. Possible reasons for the failure to find a pain placebo effect are discussed.

Conditioned open-label placebo for opioid reduction after spine surgery: a randomized controlled trial

ABSTRACT

Placebo effects have traditionally involved concealment or deception. However, recent evidence suggests that placebo effects can also be elicited when prescribed transparently as "open-label placebos" (OLPs), and that the pairing of an unconditioned stimulus (eg, opioid analgesic) with a conditioned stimulus (eg, placebo pill) can lead to the conditioned stimulus alone reducing pain. In this randomized control trial, we investigated whether combining conditioning with an OLP (COLP) in the immediate postoperative period could reduce daily opioid use and postsurgical pain among patients recovering from spine surgery. Patients were randomized to COLP or treatment as usual, with both groups receiving unrestricted access to a typical opioid-based postoperative analgesic regimen. The generalized estimating equations method was used to assess the treatment effect of COLP on daily opioid consumption and pain during postoperative period from postoperative day (POD) 1 to POD 17. Patients in the COLP group consumed approximately 30% less daily morphine milligram equivalents compared with patients in the treatment as usual group during POD 1 to 17 (-14.5 daily morphine milligram equivalents; 95% CI: [-26.8, -2.2]). Daily worst pain scores were also lower in the COLP group (-1.0 point on the 10-point scale; 95% CI: [-2.0, -0.1]), although a significant difference was not detected in average daily pain between the groups (-0.8 point; 95% CI: [-1.7, 0.2]). These findings suggest that COLP may serve as a potential adjuvant analgesic therapy to decrease opioid consumption in the early postoperative period, without increasing pain.