Nonspecific factors in drug effects: placebo personality

Association between personality traits and placebo effects: a preregistered systematic review and meta-analysis

ABSTRACT

Placebo effects are ubiquitous yet highly variable between individuals and therefore strongly affect clinical trial outcomes such as pain relief. It is unclear whether dispositional psychological traits influence responsiveness to placebo. This preregistered meta-analysis and systematic review synthesized the literature investigating the association between personality traits and placebo effects. Based on 21 studies with 798 participants, we performed formal meta-analyses for 10 different personality traits, including behavioral inhibition, fun seeking, goal-drive persistence, reward responsiveness, empathic concern, empathic fantasy, perspective-taking, personal distress, optimism, and anxiety. We did not find evidence of associations between any of these traits and magnitude of placebo effects, which was supported by equivalence tests. Furthermore, we did not find evidence for moderating factors such as placebo manipulation type (conditioning or nonconditioning) or condition (pain or nonpain). These findings challenge the notion that personality influences responsiveness to placebos and contradict its utility for identifying placebo "responders" and "nonresponders."

Use of a placebo in clinical trials

The use of a placebo control group in the evaluation of a new product is today considered by most as a necessary condition of experimental drug research. Placebo response is an essential consideration in all clinical trials. If not properly controlled, incorrect and dangerous conclusion may be inferred for a product efficacy and safety profile. However, the inclusion of a placebo group in clinical trials in neuropsychiatric research raises several ethical and scientific questions. Whereas in certain indications, such as suicidal patients and severe and psychotic depression, the use of a placebo is generally not accepted, it is difficult to assess drug efficacy. This article discusses the concept of placebo in clinical trials, the occurrence of adverse events after placebo treatment and the high response rate of placebo in neuropsychiatric clinical research. The experimental methodology to adequately control all the factors involved is also analysed and discussed.

Placebo response in depression

With its naturally fluctuating course, depression is a highly placebo-responsive condition: mean placebo response rates in antidepressant clinical trials are 30% to 40%. We review the history and terminology of placebo and the proposed mechanisms underlying the placebo response, including the physician-patient relationship and biological, sociocultural, and treatment situation factors. We identify the predictors and patterns of placebo response in depressed patients, both within and outside of the clinical trial context, and differentiate between true drug response and placebo pattern response. We discuss the strategies now being advanced to minimize the placebo response given the increased placebo drift reported in recent trials, and the ethical guidelines governing placebo administration. Potential areas for future research include the identification of biological markers of placebo response, such as functional neuroimaging and quantitative electroencephalography, the development and testing of more sophisticated, alternative research designs, and the design of valid biological tools to assess antidepressant efficacy.

Placebo effects: clinical aspects and neurobiology

Placebo effects are beneficial health outcomes not related to the relatively direct biological effects of an intervention and can be elicited by an agent that, by itself, is inert. Understanding these placebo effects will help to improve clinical trial design, especially for interventions such as surgery, CNS-active drugs and behavioural interventions which are often non-blinded. A literature review was performed to retrieve articles discussing placebo implications of clinical trials, the neurobiology of placebo effects and the implications of placebo effect for several disorders of neurological relevance. Recent research in placebo analgesia and other conditions has demonstrated that several neurotransmitter systems, such as opiate and dopamine, are involved with the placebo effect. Brain regions including anterior cingulate cortex, dorsolateral prefrontal cortex and basal ganglia have been activated following administration of placebo. A patient's expectancy of improvement may influence outcomes as much as some active interventions and this effect may be greater for novel interventions and for procedures. Maximizing this expectancy effect is important for clinicians to optimize the health of their patient. There have been many relatively acute placebo studies that are now being extended into clinically relevant models of placebo effect.

Magnitude of the placebo effect in randomized trials of antiepileptic agents

Placebo-controlled randomized trials ideally produce unbiased estimates of the treatment effect after accounting for nonpharmacological effects (regression to the mean, Hawthorne, and placebo effects). Recognizing that the magnitude of these effects may help understand why investigators need to control for them, we sought to measure this magnitude. We reviewed published meta-analyses of randomized, placebo-controlled add-on trials of antiepileptic medications versus placebo, included in the Cochrane Library. In randomized trials of antiepileptic agents for epilepsy, 9.3-16.6% of patients in the placebo arm had a >50% reduction in seizure frequency. This effect represents 20-50% of the effect observed with active agents. Because patients with epilepsy in the placebo arm of randomized trials experience a large clinical benefit due to nonpharmacological effects, randomized controlled trials are necessary to gauge the true magnitude of the treatment effect of new antiepileptic agents.

Baseline and 2- to 3-year follow-up characteristics of placebo-washout responders from the nortriptyline study of depressed 6- to 12-year-olds

Data are presented on the baseline characteristics and 2- to 3-year follow-up assessments of placebo-washout responders (PWRs) from a previously reported pharmacokinetically designed double-blind placebo-controlled trial of nortriptyline for major depressive disorder in 6- to 12-year-olds. Eleven of the 12 PWRs consented to participate in the follow-up study. At baseline, the only significant difference between the PWRs and the non-PWR subjects was that more females were PWRs. Notably, there were no significant differences with respect to severity, chronicity, age of onset, or comorbid psychopathology. The follow-up assessments showed that the rate of relapse to major depressive disorder and the rate of development of bipolarity were not significantly different for PWRs compared with non-PWRs. The authors discuss these findings vis-à-vis the adult literature and provide recommendations for the use of placebo-washout phases in future double-blind, placebo-controlled psychopharmacology trials in children.

Locus of control and alcohol placebo effects on performance in a driving simulator

Performance in a driving simulator was evaluated as a function of locus of control, perceived alcohol ingestion (no alcohol versus a no-alcohol placebo), and sex. Using a pretest-posttest design, an analysis of covariance was performed using the pretest performance on a driving simulator as the covariate. There were 10 men and 10 women in each of four groups. As predicted, the external-scoring placebo subjects made more posttest errors than did the internal-scoring placebo group or either of the no-alcohol control groups. This indicated that the external-scoring placebo subjects were more affected by what they expected to happen than their actual physiological state warranted. A difference was also found in which external-scoring women made more errors than did any other group. This was an unexpected finding which, being inconsistent with previous findings involving sex, warrants further research.

Baseline characteristics of 10-day placebo washout responders in antidepressant trials

In antidepressant drug trials, the randomized treatment phase is usually preceded by a single-blind placebo period or "washout." Ninety-four depressed patients who improved during this 10-day placebo period constitute our study focus. Analysis of baseline and postplacebo measures showed that the 10-day placebo responders in our sample were convincingly depressed at baseline and improved significantly after placebo washout. This group of patients differed from 6-week placebo responders in our randomized trials in being more mildly ill, being more chronic, containing fewer cases of primary depression, and having fewer illness precipitants. They differed from placebo nonresponders largely in manifesting milder illness symptoms across the range of psychopathology. The proportion of placebo washout responders declined in the winter months.

Drug expectations associated with perceptual characteristics: ethnic factors

For drugs, perceptual characteristics of size, form, and color have been associated with specific expectancies. Generally, capsules are perceived as stronger than tablets, larger capsules are seen as stronger than smaller ones, and some capsule colors have specifically ascribed expectations of drug action. This study replicated previous work with black subjects to assess perceptual constancies in drug expectancy between ethnic groups. 50 black subjects classified 12 colored capsules into 5 categories of drug action, rank-ordered 6 capsule sizes for relative strength, and compared a tablet and capsule for strength. Appreciable differences between white and black samples were noted for size-strength relationships and drug action expectancy associated with capsule colors. Results suggest ethnic implications for drug efficacy and compliance, with blacks less influenced by perceptual characteristics of drugs.

Relationship of perceptual characteristics to efficacy of placebos

The placebo was acknowledged as a potent agent associated with a myriad of psychological, therapeutic, and behavioral effects. Given the widespread use and efficacy of placebos, major needs relative to more accurate conceptualization, appreciation, and effective use of properties were discussed. Emphasis was placed on considerations of the placebo as a complex stimulus. The physical and perceptual characteristics of placebos were reviewed in regard to efficacy, with specific attention to route of administration, preparation form, size and dose, color, taste, and interpretation of ‘pharmacological’ agentry. Conclusions were directed to facilitating optimal effectiveness of a placebo. Directions for further research were suggested, and failure to consider the differential stimuli of placebos was viewed as contributing to the potential unwitting confounding in studies.