What is causing the reduced drug-placebo difference in recent schizophrenia clinical trials and what can be done about it?

Placebo effects of repetitive transcranial magnetic stimulation on negative symptoms and cognition in patients with schizophrenia spectrum disorders: a systematic review and meta-analysis

Background

Negative symptoms and cognitive impairments are highly frequent in schizophrenia spectrum disorders (SSD), associated with adverse functional outcomes and quality of life. Repetitive transcranial magnetic stimulation (rTMS) has been considered a promising therapeutic option in SSD. However, placebo effects of rTMS on these symptoms remained unclear.

Objective

To investigate placebo effects of rTMS on alleviating negative symptoms and cognitive impairment in patients with SSD and to explore potential moderators.

Methods

We systematically searched five electronic databases up to 15 July 2023. Randomized, double-blind, sham-controlled trials investigating effects of rTMS on negative symptoms or cognition in patients with SSD were included. The pooled placebo effect sizes, represented by Hedges' g, were estimated using the random-effects model. Potential moderators were explored through subgroup analysis and meta-regression.

Results

Forty-four randomized controlled trials with 961 patients (mean age 37.53 years; 28.1% female) in the sham group were included. Significant low-to-moderate pooled placebo effect sizes were observed for negative symptoms (g=0.44, p<0.001), memory (g=0.31, p=0.010), executive function (g=0.35, p<0.001), working memory (g=0.26, p=0.004), and processing speed (g=0.36, p=0.004). Subgroup analysis indicated that placebo effects were affected by sham stimulation methods, rTMS targeting approaches, and stimulation frequency.

Conclusions

Placebo effects of rTMS on negative symptoms and cognition in patients with SSD are significant in a small-to-moderate magnitude, which might be mediated by rTMS parameters. Our findings will provide new insights for practitioners to further optimize and establish standardized rTMS protocols for future RCTs tackling cardinal symptoms in SSD.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42023390138.

Evaluation of the efficacy and safety of Yukwool-tang for major depressive disorder in women: A randomized, double blinded, placebo-controlled, parallel trial

BACKGROUND

Major depressive disorder (MDD) occurs more often in women than that in men due to various complex causes. This study aimed to evaluate the effectiveness and safety of Yukwool-tang (YWT) for MDD in women.

METHODS

A total of 72 patients diagnosed with MDD and Korean version of the Hamilton Depression Rating Scale (K-HDRS) ≥ 14 points were randomly assigned to the YWT or placebo group, and 1 bottle (30 mg) of No-S solution and placebo was administered to the YWT and placebo groups, respectively, orally thrice a day for 8 weeks. The evaluation was conducted through K-HDRS, Korean version of the Beck Depression Inventory (BDI-K), Korean version of the Beck Hopelessness Scale (K-BHS), Korean version of the Insomnia Severity Index (ISI-K), State-Trait Anxiety Inventory (STAI-K), EuroQol-5 dimension (EQ-5D), and Pattern Identifications Tool for Depression (PITD). Fifty patients completed the trial.

RESULTS

In the YWT group, the K-HDRS, BDI-K, K-BHS, ISI-K, STAI-K, and EQ-5D scores changed significantly at the 8th week, but there were no significant differences with the placebo. In subgroup analysis, the K-BHS score with an initial K-HDRS score < 18 points was significantly decreased compared to placebo at the 12th week (P < .05). In the YWT group, the ratio of Stagnation of Liver Gi () was the highest, but Dual Deficiency of the Heart and Spleen () became the highest after administration, which was also the highest in the placebo group both before and after administration.

CONCLUSION

YWT improved depression and accompanying symptoms in women with MDD, although it was not significant compared to placebo, and it might be effective in improving the degree of hopelessness. The effect of YWT will become relatively clear through further research that can overcome certain limitations.

Challenges in the clinical development of non-D2 compounds for schizophrenia

Schizophrenia is a chronic, heterogeneous, severe psychiatric disorder characterized by a spectrum of symptomology and is associated with substantial morbidity and mortality. For the last 70 years, available treatments have shared blockade of dopamine D2 receptors as their primary mechanism of action (MOA), the efficacy of which has been limited by incomplete resolution of all symptoms as well as treatment non-response in a select subset of patients. In addition, antipsychotics are associated with class-related side effects attributed to this primary MOA, including extrapyramidal symptoms (EPS). The need for non-D2 treatment options for patients which offer a novel risk/benefit profile is therefore apparent. There has been substantial investment in the research and development of non-D2 drug candidates. However, none of these programs have received successful regulatory approval by the FDA (as of Oct 2022). In this article, the scale of industry-sponsored clinical trials for D2-based investigational pharmacological treatments in schizophrenia was quantified and compared with investigational compounds with non-D2 MOAs. In a dataset of 545 clinical trials identified in ClinicalTrials.gov from January 2002 to July 2022, total enrollments in trials of non-D2-based compounds for the treatment of schizophrenia summed to approximately 34,000 patients, compared with 27,144 patients for D2-based compounds. These data indicate that there remains substantial and ongoing investment in the development of novel non-D2 options for schizophrenia, with a success rate measured by regulatory approval that is well-below recent benchmarks for the broader category of CNS drugs. Improved trial design, conduct, endpoints, and analyses/methods may influence signal detection and reliability to support development and registration of non-D2 compounds.

The future of psychopharmacology: a critical appraisal of ongoing phase 2/3 trials, and of some current trends aiming to de-risk trial programmes of novel agents

Despite considerable progress in pharmacotherapy over the past seven decades, many mental disorders remain insufficiently treated. This situation is in part due to the limited knowledge of the pathophysiology of these disorders and the lack of biological markers to stratify and individualize patient selection, but also to a still restricted number of mechanisms of action being targeted in monotherapy or combination/augmentation treatment, as well as to a variety of challenges threatening the successful development and testing of new drugs. In this paper, we first provide an overview of the most promising drugs with innovative mechanisms of action that are undergoing phase 2 or 3 testing for schizophrenia, bipolar disorder, major depressive disorder, anxiety and trauma-related disorders, substance use disorders, and dementia. Promising repurposing of established medications for new psychiatric indications, as well as variations in the modulation of dopamine, noradrenaline and serotonin receptor functioning, are also considered. We then critically discuss the clinical trial parameters that need to be considered in depth when developing and testing new pharmacological agents for the treatment of mental disorders. Hurdles and perils threatening success of new drug development and testing include inadequacy and imprecision of inclusion/exclusion criteria and ratings, sub-optimally suited clinical trial participants, multiple factors contributing to a large/increasing placebo effect, and problems with statistical analyses. This information should be considered in order to de-risk trial programmes of novel agents or known agents for novel psychiatric indications, increasing their chances of success.

Nocebo Response in Attention Deficit Hyperactivity Disorder: Meta-Analysis and Meta-Regression of 105 Randomized Clinical Trials

OBJECTIVE

To determine nocebo response in ADHD, identify covariates modifying nocebo response, and study the relationship between nocebo response and drug safety.

METHOD

Systematic review of randomized, double-blind, placebo-controlled clinical trials (RCT) investigating the efficacy and safety of pharmacological interventions for ADHD patients. The influence of covariates was studied using meta-regression.

RESULTS

A total of 105 studies with 8,743 patients in placebo arms were included. Slightly over half (55.5%) of the patients experienced adverse events (AE) while receiving placebo. Nocebo response was associated positively with age, treatment length and method for collecting AEs. Studies with the largest nocebo response showcased the greatest drug response and the best outcome for drug safety.

CONCLUSION

Nocebo response in ADHD RCTs is remarkable, showing a positive relationship with drug response, and a negative relationship with drug safety.

Expert consensus recommendations on the use of randomized clinical trials for drug approval in psychiatry- comparing trial designs

The use of randomized clinical trials, in particular placebo-controlled trials, for drug approval, is the subject of long-standing debate in the scientific community and beyond. This study offers consensus recommendations from clinical and academic experts to guide the selection of clinical trial design in psychiatry. Forty-one highly cited clinical psychiatrists and/or researchers participated in a Delphi survey. Consensus statements were developed based on the findings of a published, peer-reviewed systematic review. Participants evaluated statements in two survey rounds, following the Delphi method. The expert panel achieved consensus on 7 of 21 recommendations regarding the use of randomized clinical trials. The endorsed recommendations were: (i) Results from placebo-controlled trials are the most reliable and (ii) are necessary despite the growing placebo-effect; (iii) it is ethical to enroll patients in placebo-arms when established treatment is available, if there is no evidence of increased health risk; (iv) There is a need to approve new drugs with the same efficacy as existing treatments, but with different side-effect profiles; (v) Non-inferiority trials incur an increased risk of approving ineffective medications; (vi) The risk of approving an ineffective drug justifies trial designs that incur higher costs, and (vii) superiority trials incur the risk of rejecting potentially efficacious treatments. The endorsed recommendations inform the choice of trial-design appropriate for approval of psychopharmacological drugs. The recommendations strongly support the use of randomized clinical trials in general, and the use of placebo-controlled trials in particular.

Placebo Response in Trials of Negative Symptoms in Schizophrenia: A Critical Reassessment of the Evidence

BACKGROUND

Summarizing evidence from clinical trials of patients with schizophrenia with predominant or prominent negative symptoms (NS), a prior meta-analysis reported a large placebo effect in negative symptoms (Cohen's d = 2.909). Assuming that such an effect was clinically not plausible, we performed a critical re-assessment and an update of the previous results with newly available data from add-on and monotherapy studies.

STUDY DESIGN

Random-effect meta/regression analysis of trials that focused on predominant or prominent NS; and adopted a double-blind, randomized, placebo-controlled design. The final pooled meta-analytic database, based on the available add-on and monotherapy studies combined, included 24 publications containing data on a total of 25 studies (21 add-on, 4 monotherapy).

STUDY RESULTS

The pooled overall estimate for the placebo effect from the primary analysis for all included studies had a medium effect size, with a Cohen's d value of 0.6444 (SE = 0.091). The estimates were similar in the add-on and monotherapy studies. Meta-regression indicated that the high placebo response was significantly associated with clinical trial characteristics, including the high ratio of patients assigned to active vs. placebo treatment and short trial duration.

CONCLUSIONS

These results represent a major downward correction for a current effect size estimate of the placebo response in the negative symptoms of schizophrenia. Our findings also pinpoint certain clinical trial characteristics, which may serve as important predictors of the placebo response. The knowledge of these factors can have important implications for drug development and trial design for new drugs for negative symptoms of schizophrenia.

Association of End Point Definition and Randomized Clinical Trial Duration in Clinical Trials of Schizophrenia Medications

IMPORTANCE

Facilitating the development of safe and effective medications for schizophrenia is a public health imperative.

OBJECTIVES

To evaluate the association of shortening randomized clinical trial (RCT) duration with the modification of the Positive and Negative Syndrome Scale (PANSS) for the design of RCTs of medications for schizophrenia and to offer perspective on an alternative regulatory pathway to the historically accepted trial duration and response assessment.

DATA SOURCES

A database was created consisting of clinical trial data from 32 placebo-controlled RCTs of 8 atypical antipsychotic drugs approved by the US Food and Drug Administration (FDA) between January 1, 2001, and December 31, 2015. The database included information on total and individual PANSS item ratings, demographic characteristics, disposition, and adverse events (AEs).

STUDY SELECTION

All clinical trials submitted to 8 new drug applications of atypical antipsychotic drugs were selected.

DATA EXTRACTION AND SYNTHESIS

Quality control checks were performed to ensure that the collected data were consistent with the reported results of each trial. Data were collected from March 15, 2015, to September 30, 2015. Data analysis was conducted from October 1, 2015, to June 20, 2016.

MAIN OUTCOMES AND MEASURES

The following analyses were performed: (1) longitudinal assessment of mean change from baseline in total PANSS score, (2) correlation analyses between change from baseline in total PANSS score at week 6 and earlier time points, (3) concordance analyses of outcomes across trials between week 6 and earlier time points using total PANSS and modified PANSS, and (4) analyses of time course of treatment-emergent AEs.

RESULTS

The final database contained data from 14 219 participants enrolled in 32 drug trials; 9805 of 14 219 participants (69.0%) were male and were either white (7183 [50.5%]) or black (4346 [30.6%]) individuals. The mean (SD) age during treatment was 38.9 (10.9) years, and the mean (SD) age at schizophrenia diagnosis was 25 (8.5) years. Statistically significant separation between treatment response and placebo response was observed after 1 week of treatment. The overall concordance rate across treatment groups steadily increased from week 1 to week 4 (68.0% for week 1, 74.0% for week 2, 83.0% for week 3, and 93.0% for week 4). Trends in AE occurrence were evident by week 1 and percentage of AEs were similar across weeks 3, 4, and 6. The overall concordance rate between change from baseline in the modified PANSS score and change from baseline in the total PANSS score was 93.0% (80 of 86 treatment groups) at week 4 and 97.7% (84 of 86 treatment groups) at week 6. Shortening the trial duration to 4 weeks increased the required sample size to 502 participants. Using the modified PANSS as the end point, the sample size for a 4-week trial was 402 participants and 296 participants for a 6-week trial.

CONCLUSIONS AND RELEVANCE

Findings from this analysis suggest that there is the potential to streamline the design of schizophrenia drug clinical trials. Trial sponsors may consider incorporating these strategies and are encouraged to consult with the FDA early in the drug development process.

Strategies to minimize placebo effects in research investigations

Placebo-controlled trials are the research standard to evaluate new interventions for which there is no standard of care. While lessening performance and detection bias, such design provides a direct mode of comparison against the probed intervention. Still, using placebo arms may pose new challenges to the design, conduct and analysis of clinical trials. This is particularly relevant in circumstances of non-additivity between the therapeutic and the placebo effects, if the outcome of interest has floor or ceiling effects, or when the predicted effect size of the intervention is large and leads to small sample sizes. There are several possible strategies to mitigate the confounding effects of the placebo, each relevant to specific clinical trial designs. This chapter puts into context the new challenges created by the placebo effect, discusses possible ways around them, and explores the future of the field.

Comprehensive review of the research employing the schizophrenia cognition rating scale (SCoRS)

This review of research utilizing the Schizophrenia Cognition Rating Scale (SCoRS) outlines the development, evaluation, validation, and implementation of the SCoRS to assess whether the scale meets the criteria as a functional co-primary as defined by the MATRICS-CT initiative. Interview-based co-primary assessments should be: 1) practical and easy to administer for a clinician or researcher; 2) validated in individuals with schizophrenia; 3) contain the relevant areas of cognition and functioning applicable to schizophrenia; 4) able to assess all phases and severity levels of schizophrenia; 5) capable of monitoring disease progression; 6) minimal burden to patients; and 7) sensitive to assess treatment effects. A review of the literature was conducted to present information on the development, psychometric properties and usage of the SCoRS. Review of the development of the SCoRS followed the parameters outlined for scale development on content expert validation and feedback. The SCoRS shows good psychometric properties in various studies, and demonstrates low burden on clinicians and patients. The items measure global concepts that do not require notable cultural modification, making international use feasible. While multiple performance-based tests in cognition and functional outcomes are available, there is a need for a multi-domain, interview-based assessment of cognitive progression and treatment response in clinical trials. The SCoRS appears to meet many of the criteria for an optimal co-primary measure for schizophrenia cognition clinical trials as defined in the MATRICS-CT initiative.

Is High Placebo Response Really a Problem in Depression Trials? A Critical Re-analysis of Depression Studies

Objective: We investigated the accuracy of the often-stated assumption that placebo nonadditivity and an increasing placebo response are major problems in clinical trials and the cause of a trend for smaller treatment effects observed in clinical trials for major depressive disorder (MDD) in recent years. Method of research: We reviewed data from 122 MDD trials conducted between the years 1983 and 2010 (analyzed originally by Undurraga and Baldessarini in 2012) to determine whether the data support the assumption of placebo additivity. Statistical techniques, such as conventional least squares regression, orthogonal least squares regression and locally weighted loess smoothing, were applied to the data set. Results: Re-analysis of the data set showed the active and placebo responses to be highly correlated, to the degree that would be expected assuming placebo additivity, when random variability in both active and placebo response is considered. Despite the placebo responses in MDD trials increasing up to approximately the year 1998, we found no evidence that it has continued to increase since this date, or that it has been the cause of smaller reported treatment effects in recent years. Conclusion: Attempts to reduce the placebo response are unlikely to increase the treatment effect since they are likely to reduce drug nonspecific effects in the treatment arm by a similar amount. Thus, it should come as no surprise that trial designs set up with the sole purpose of reducing placebo response fail to discernibly benefit our ability to identify new effective treatments.

The effect of minocycline on symptoms in schizophrenia: Results from a randomized controlled trial

BACKGROUND

Studies have hypothesized that immunological abnormalities might contribute to schizophrenia, and basic science studies, as well as several clinical trials suggest that minocycline could be efficacious in ameliorating both positive and negative symptoms of schizophrenia. In this study we examined the effect of minocycline on schizophrenia in a large randomized controlled trial.

METHODS

We performed a 16-week, multi-center, double-blind, randomized, placebo-controlled study on 200 subjects with schizophrenia or schizoaffective disorder randomized to receive either minocycline (200 mg/day, n = 100), or placebo (n = 100) as an add-on to anti-psychotic treatment. The primary outcome measure was the PANSS total score.

RESULTS

Mixed models for repeated measures showed no significant difference between minocycline and placebo for total PANSS (p = 0.862), PANSS subscales, CGI or BACS.

CONCLUSIONS

Minocycline did not improve symptoms or cognition in schizophrenia.

Neuropathic pain clinical trials: factors associated with decreases in estimated drug efficacy

Multiple recent pharmacological clinical trials in neuropathic pain have failed to show beneficial effect of drugs with previously demonstrated efficacy, and estimates of drug efficacy seems to have decreased with accumulation of newer trials. However, this has not been systematically assessed. Here, we analyze time-dependent changes in estimated treatment effect size in pharmacological trials together with factors that may contribute to decreases in estimated effect size. This study is a secondary analysis of data from a previous published NeuPSIG systematic review and meta-analysis, updated to include studies published up till March 2017. We included double-blind, randomized, placebo-controlled trials examining the effect of drugs for which we had made strong or weak recommendations for use in neuropathic pain in the previously published review. As the primary outcome, we used an aggregated number needed to treat for 50% pain reduction (alternatively 30% pain reduction or moderate pain relief). Analyses involved 128 trials. Number needed to treat values increased from around 2 to 4 in trials published between 1982 and 1999 to much higher (less effective) values in studies published from 2010 onwards. Several factors that changed over time, such as larger study size, longer study duration, and more studies reporting 50% or 30% pain reduction, correlated with the decrease in estimated drug effect sizes. This suggests that issues related to the design, outcomes, and reporting have contributed to changes in the estimation of treatment effects. These factors are important to consider in design and interpretation of individual study data and in systematic reviews and meta-analyses.

A phase 2, randomized, placebo-controlled study of the efficacy and safety of TAK-063 in subjects with an acute exacerbation of schizophrenia

INTRODUCTION

TAK-063 is a potent, selective inhibitor of phosphodiesterase 10A, an enzyme selectively expressed in medium spiny neurons of the striatum. This randomized, parallel-group study evaluated the efficacy and safety of 20-mg daily TAK-063 versus placebo in subjects with acutely exacerbated symptoms of schizophrenia (NCT02477020).

METHODS

Adults aged 18 to 65 with diagnosed schizophrenia and psychotic symptoms that exacerbated within 60 days before screening were included. Subjects who discontinued psychotropic medications before screening were randomized 1:1 to 6 weeks of placebo (n = 81) or 20-mg TAK-063 (n = 83). Weekly efficacy visits were conducted during the treatment period, and dose de-escalation was allowed (blinded) to 10-mg TAK-063 for intolerability.

RESULTS

The primary endpoint, change from baseline in the Positive and Negative Syndrome Scale total score at week 6, was not achieved (least-squares mean difference vs placebo [standard error] = -5.46 [3.44]; p = 0.115). Secondary endpoints were generally supportive of antipsychotic efficacy. Consistent with previous phase 1 studies, TAK-063 was safe and well tolerated, and most adverse events were mild or moderate in severity and did not result in discontinuation. No deaths occurred, and the incidence of akathisia and dystonia, categories of extrapyramidal syndromes, was more frequent in the TAK-063 group than placebo.

CONCLUSIONS

Although the study did not meet the primary endpoint (effect size = 0.308), the effects of TAK-063 on the primary and secondary endpoints may be suggestive of antipsychotic activity. Interpretation of these results is confounded by a relatively high placebo effect and a lack of dose-ranging or active reference.

The past and future of novel, non-dopamine-2 receptor therapeutics for schizophrenia: A critical and comprehensive review

Since the discovery of chlorpromazine in the 1950's, antipsychotic drugs have been the cornerstone of treatment of schizophrenia, and all attenuate dopamine transmission at the dopamine-2 receptor. Drug development for schizophrenia since that time has led to improvements in side effects and tolerability, and limited improvements in efficacy, with the exception of clozapine. However, the reasons for clozapine's greater efficacy remain unclear, despite the great efforts and resources invested therewith. We performed a comprehensive review of the literature to determine the fate of previously tested, non-dopamine-2 receptor experimental treatments. Overall we included 250 studies in the review from the period 1970 to 2017 including treatments with glutamatergic, serotonergic, cholinergic, neuropeptidergic, hormone-based, dopaminergic, metabolic, vitamin/naturopathic, histaminergic, infection/inflammation-based, and miscellaneous mechanisms. Despite there being several promising targets, such as allosteric modulation of the NMDA and α7 nicotinic receptors, we cannot confidently state that any of the mechanistically novel experimental treatments covered in this review are definitely effective for the treatment of schizophrenia and ready for clinical use. We discuss potential reasons for the relative lack of progress in developing non-dopamine-2 receptor treatments for schizophrenia and provide recommendations for future efforts pursuing novel drug development for schizophrenia.

Predictors of Placebo Response in Pharmacological Clinical Trials of Negative Symptoms in Schizophrenia: A Meta-regression Analysis

We conducted a meta-regression analysis of all double-blind, randomized, placebo-controlled clinical trials (DBRCTs) reporting effects of drug and placebo on negative symptoms in people with stable schizophrenia and predominant or prominent negative symptoms to assess predictors of placebo response in these individuals. We used Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines for systematic reviews and meta-analyses to conduct a systematic literature search to identify DBRCTs assessing treatment efficacy on negative symptoms, as primary outcome, in patients with stable schizophrenia and predominant or prominent negative symptoms. We used Cohen's d, with 95% CIs, as the effect size measure for placebo response, based on negative symptom change scores from baseline to endpoint (range 4 to 24 wk) in the placebo-treated group. We included 18 DBRCTs from 17 publications, assessing the effect of 13 drugs vs placebo on negative symptoms and comprising 998 patients, in the meta-regression analyses. Overall, drugs showed greater efficacy than placebo in reducing negative symptoms, with small effect size (Cohen's d: 0.208, P = .020). Placebo response was significant (P < .001) and clinically relevant (Cohen's d: 2.909), but there was significant heterogeneity and high risk of publication bias. Multivariable meta-regression analyses showed that larger numbers of arms in the trial, larger numbers of study sites and industry sponsorship were significant moderators of placebo response in this population. Our results suggest that some clinical trial design and operational factors affect the level of placebo response in such studies, thus highlighting the need for designs better suited to assess these outcomes.

Meta-analysis of Placebo Response in Randomized Clinical Trials of Antipsychotic Drugs Using PANSS Focusing on Different Approaches to the Handling of Missing Data

BACKGROUND AND OBJECTIVE

Schizophrenia treatment has been shifting to resocialization by efficacious antipsychotic drugs. However, even some of the pivotal studies of approved new antipsychotic drugs with proven efficacy had failed due to high placebo response. The aim of this study was to identify the potential factors affecting placebo response by meta-analysis for randomized clinical trials for antipsychotic drugs using Positive and Negative Syndrome Scale (PANSS) focusing on the current methodological change in the handling of missing data [from last observation carried forward (LOCF) to mixed-effect models for repeated measures (MMRM)] for successful future clinical trials.

METHODS

Recent trends in the degree of placebo response were investigated between publication year (1993 to 2016) and the mean change of PANSS total score in the placebo arm. The potential factors affecting the degree of placebo response, such as study design and operational factors, were analyzed separately by meta-regression for LOCF- and MMRM-based data.

RESULTS

There was no correlation between publication year and the mean change of PANSS score in the placebo arm in schizophrenia studies of 10 years applying MMRM. The number of countries and treatment setting in MMRM-based data and study duration in LOCF-based data were significantly associated with placebo response.

CONCLUSION

Placebo response in schizophrenia clinical trials published between 2007 and 2016 has not increased over time. Differences in the healthcare environment among countries were suggested to affect the evaluation of antipsychotic drugs. Further analyses on the potential factors of placebo response for MMRM-based data are required.

A Machine Learning Approach to Identifying Placebo Responders in Late-Life Depression Trials

OBJECTIVE

Despite efforts to identify characteristics associated with medication-placebo differences in antidepressant trials, few consistent findings have emerged to guide participant selection in drug development settings and differential therapeutics in clinical practice. Limitations in the methodologies used, particularly searching for a single moderator while treating all other variables as noise, may partially explain the failure to generate consistent results. The present study tested whether interactions between pretreatment patient characteristics, rather than a single-variable solution, may better predict who is most likely to benefit from placebo versus medication.

METHODS

Data were analyzed from 174 patients aged 75 years and older with unipolar depression who were randomly assigned to citalopram or placebo. Model-based recursive partitioning analysis was conducted to identify the most robust significant moderators of placebo versus citalopram response.

RESULTS

The greatest signal detection between medication and placebo in favor of medication was among patients with fewer years of education (≤12) who suffered from a longer duration of depression since their first episode (>3.47 years) (B = 2.53, t(32) = 3.01, p = 0.004). Compared with medication, placebo had the greatest response for those who were more educated (>12 years), to the point where placebo almost outperformed medication (B = -0.57, t(96) = -1.90, p = 0.06).

CONCLUSION

Machine learning approaches capable of evaluating the contributions of multiple predictor variables may be a promising methodology for identifying placebo versus medication responders. Duration of depression and education should be considered in the efforts to modulate placebo magnitude in drug development settings and in clinical practice.

A Randomized, Double-Blind, Placebo-Controlled Clinical Trial of Tocilizumab, An Interleukin-6 Receptor Antibody, For Residual Symptoms in Schizophrenia

Evidence from preclinical, epidemiological, and human studies indicates that inflammation, and in particular elevated interleukin-6 (IL-6) activity, may be related to clinical manifestations and pathophysiology of schizophrenia. Furthermore, studies in preclinical models suggest that decreasing IL-6 activity may mitigate or reverse some of these deficits. The purpose of this trial was to test whether an IL-6 receptor antibody, tocilizumab, would improve residual positive and negative symptoms and cognitive deficits in schizophrenia. We randomized 36 clinically stable, moderately symptomatic (i.e., Positive and Negative Syndrome Scale (PANSS) >60) individuals with schizophrenia to 3 monthly infusions of 8 mg/kg tocilizumab or placebo (normal saline). The primary outcome was effect at week 12 on the PANSS Total Score. Effects on the MATRICS, other PANSS subscales, Clinical Global Impression, and Global Assessment of Functioning were secondary outcomes. There were no observed treatment effects on any behavioral outcome measure. Baseline C-reactive protein (CRP) or cytokine levels did not predict treatment outcome, nor were there correlations between changes in these inflammatory markers and the measured outcomes. As expected, IL-6 and IL-8 increased, while CRP decreased, in the tocilizumab group compared with the placebo group. This study did not reveal any evidence that an IL-6 receptor antibody affects behavioral outcomes in schizophrenia. One potential explanation is the lack of capacity of this agent to penetrate the central nervous system. Additional trials of medications aimed at targeting cytokine overactivity that act directly on brain function and/or treatment in early-stage psychosis populations are needed.

Use of Placebo in Clinical Trials of Psychotropic Medication

This position paper has been substantially revised by the Canadian Psychiatric Association's Research Committee and approved for republication by the CPA's Board of Directors on March 31, 2017. The original position paper¹ was developed by the Scientific and Research Council and approved by the Board of Directors on October 4, 1996.

Can knowledge of Placebo and Nocebo Mechanisms Help Improve Randomized Clinical Trials?

Over the last decade, there has been a substantial increase in negative results from randomized controlled trials (RCTs), which may be due to an increasing placebo response among other factors. Currently, identification and exclusion of placebo responders from trials are attempted to overcome this problem, but so far the success of these approaches has been limited. At the same time, the placebo-mechanism literature has highlighted how contextual factors, such as patients' expectations, interfere with the effect of drug administration, leading to a certain degree of uncertainty in RCTs. In this chapter, we review the current challenges of RCTs including the uncertainties of the active arm, the placebo arm, the additivity assumption, and the double-blind procedure. We use the placebo-mechanism literature to debate the strengths and weaknesses of attempts to identify and exclude placebo responders from trials. Finally, we illustrate how insights from the placebo-mechanism literature may point to new ways of improving RCTs.

Dose equivalents for second generation long-acting injectable antipsychotics: The minimum effective dose method

BACKGROUND

The concept of dose equivalence of depot medication is important for many scientific and clinical purposes.

METHODS

A systematic literature search on four second-generation antipsychotics available as long-acting injectable drugs and haloperidol was conducted. We used the minimum effective dose method which is based on randomized fixed dose studies where the smallest dose which was significantly more efficacious than placebo in the primary outcome was declared as minimum effective dose. We calculated equivalent doses from acute phase studies but we also reported the minimum effective doses found in relapse prevention studies.

RESULTS

The acute phase minimum effective doses/olanzapine equivalents were: aripiprazole lauroxil 441mg (300mg aripiprazole)/4wks/0.71; aripiprazole 400mg/4weeks/0.95 (aripiprazole maintena); paliperidone palmitate 25mg/4weeks/0,06; risperidone 25mg/2weeks/0,12; RBP-7000 90mg/4weeks/0,21; olanzapine 210mg/2weeks/1.

CONCLUSIONS

The minimum effective dose method is an operationalized and evidence-based approach for determining antipsychotic dose equivalence which can also be applied to long-acting injectable formulations. Doses may not have been chosen low enough to find the truly minimum effective dose. Comparisons with other methods will be necessary to come to ultimate conclusions.

A case study in identifying targeted patients population in major depressive disorder by enhanced enrichment design

Despite advances in clinical trial design, failure rates near 80% in phase 2 and 50% in phase 3 have recently been reported. The challenges to successful drug development are particularly acute in central nervous system trials such as for pain, schizophrenia, mania, and depression because high-placebo response rates lessen assay sensitivity, diminish estimated treatment effect sizes, and thereby decrease statistical power. This paper addresses the importance of rigorous patient selection in major depressive disorder trials through an enhanced enrichment paradigm. This approach led to a redefinition of an ongoing, blinded phase 3 trial algorithm for patient inclusion (1) to eliminate further randomization of transient placebo responders and (2) to exclude previously randomized transient responders from the primary analysis of the double blind phase of the trial. It is illustrated for a case study for the comparison between brexpiprazole + antidepressant therapy and placebo + antidepressant therapy. Analysis of the primary endpoint showed that efficacy of brexpiprazole versus placebo could not be established statistically if the original algorithm for identification of placebo responders was used, but the enhanced enrichment approach did statistically demonstrate efficacy. Additionally, the enhanced enrichment approach identified a target population with a clinically meaningful treatment effect. Through its successful identification of a target population, the innovative enhanced enrichment approach enabled the demonstration of a positive treatment effect in a very challenging area of depression research.

Variation in Placebo Effect Sizes in Clinical Trials of Oral Interventions for Management of the Behavioral and Psychological Symptoms of Dementia (BPSD): A Systematic Review and Meta-Analysis

Increasing placebo effect sizes over time have been reported in randomized controlled trials (RCTs) for outcomes related to psychiatric symptoms. The Neuropsychiatric Inventory (NPI) is a key outcome measure in clinical trials of the behavioral and psychological symptoms of dementia (BPSD). Accurate placebo effect size estimates for NPI are needed for sample size calculations in order to adequately power future studies. This study investigated variation in placebo effect sizes for NPI in RCTs testing oral interventions for BPSD. A search of PubMed was conducted in April 2016 for two-armed, double-blinded, placebo-controlled RCTs testing any oral intervention for management of BPSD using the NPI. Meta-analysis was conducted of baseline versus end of treatment placebo group data of included studies. Twenty-five RCTs published from 2000 to 2015 were included. Substantial variation in placebo effect sizes was detected. Participants in placebo groups showed greater improvements in recent studies compared with earlier studies. Subgroup analyses indicated robustness of this finding. From 2000 to 2008 there was no significant change in total NPI scores within placebo groups (12 studies; 1,056 participants), whereas from 2009 to 2015 there was significant improvement (mean difference: -2.68; 95% confidence interval: -4.38, -0.99; z = 3.10; p = 0.002, random effects; I² = 76%; 13 studies; 1,170 participants). This increase in NPI effect sizes in placebo groups has important implications for power calculations for future clinical trials of BPSD. Effect size estimates for NPI need to be based on more recent studies.

New drug developments in psychosis: Challenges, opportunities and strategies

All currently approved drugs for schizophrenia work mainly by dopaminergic antagonism. While they are efficacious for psychotic symptoms, their efficacy is limited for negative symptoms and cognitive deficits which underlie the substantive disability in this illness. Recent insights into the biological basis of schizophrenia, especially in relation to non-dopaminergic mechanisms, have raised the efforts to find novel and effective drug targets, though with relatively little success thus far. Potential impediments to novel drug discovery include the continued use of symptom based disease definitions which leads to etiological and pathophysiological heterogeneity, lack of valid preclinical models for drug testing, and design limitations in clinical trials. These roadblocks can be addressed by (i) characterizing trans-diagnostic, translational pathophysiological dimensions as potential treatment targets, (ii) efficiency, accountability and, transparency in approaches to the clinical trials process, and (iii) leveraging recent advances in genetics and in vitro phenotypes. Accomplishing these goals is urgent given the significant unmet needs in the pharmacological treatment of schizophrenia. As this happens, it is imperative that clinicians employ optimal dosing, measurement-based care, and other best practices in utilizing existing treatments to optimize outcomes for their patients today.

5-HT6 Receptor Antagonist as an Adjunct Treatment Targeting Residual Symptoms in Patients With Schizophrenia: Unexpected Sex-Related Effects (Double-Blind Placebo-Controlled Trial)

BACKGROUND

Treating patients who experience residual psychotic symptoms during remission of schizophrenia remains one of the most challenging problems. The mechanisms underlying these symptoms differ from those of acute hallucinations and delusions. 5-HT6 receptor antagonists have been considered promising agents in treatment of residual psychotic symptoms and cognitive dysfunction. The aim of the study was to assess the efficacy of a selective 5-HT6 inhibitor Avisetron in the reduction of residual psychotic symptoms in patients with schizophrenia on stable antipsychotic therapy.

METHODS

Eighty clinically stable outpatient subjects with schizophrenia with residual psychotic symptoms were randomized in a double-blind manner to 6 weeks of Avisetron or placebo at 1:1 ratio. Subjects received 8 mg of Avisetron or placebo on top their stable antipsychotic treatment. Standard clinical scales and cognitive tests were used for endpoint assessment. The primary efficacy endpoint was the mean reduction of total Positive and Negative Syndrome Scale score after 6 weeks of treatment.

RESULTS

No significant differences in the primary and secondary endpoints were found between the groups. However, based on the subgroup analysis, the significant improvement of total Positive and Negative Syndrome Scale score and residual psychotic symptoms was observed in female patients.

CONCLUSIONS

It was a negative study with unexpected benefits of the drug only in females. We hypothesized that the role of patients' sex can impact the treatment response to serotonergic drugs in general. We suggest a possible synergistic interaction between estrogen and Avisetron by means of modulating the effect of estrogens on the serotonergic system. Future studies targeting the sex-related effects of serotonergic drugs are warranted.

Manipulating the Placebo Response in Experimental Pain by Altering Doctor's Performance Style

Background: Performance is paramount in traditional healing rituals. From a Western perspective, such performative behavior can be understood principally as inducing patients’ faith in the performer’s supernatural healing powers and effecting positive changes through the same mechanisms attributed to the placebo response, which is defined as improvement of clinical outcome in individuals receiving inactive treatment. Here we examined the possibility of using theatrical performance tools, including stage directions and scripting, to reproducibly manipulate the style and content of a simulated doctor–patient encounter and influence the placebo response in experimental pain.

Methods: A total of 122 healthy volunteers (18–45 years, 76 men) exposed to experimental pain (the cold pressor test) were assessed for pain threshold and tolerance before and after receiving a placebo cream from a “doctor” impersonated by a trained actor. The actor alternated between two distinct scripts and stage directions, i.e., performance styles created by a theater director/playwright, one emulating a standard doctor–patient encounter (scenario A) and the other emphasizing attentiveness and strong suggestion, elements also present in ritual healing (scenario B). The placebo response size was calculated as the %difference in pain threshold and tolerance after exposure relative to baseline. In addition, subjects demonstrating a ≥30% increase in pain threshold or tolerance relative to baseline were defined as responders. Each encounter was videotaped in its entirety.

Results: Inspection of the videotapes confirmed the reproducibility and consistency of the distinct scenarios enacted by the “doctor”-performer. Furthermore, scenario B resulted in a significant increase in pain threshold relative to scenario A. Interestingly, this increase derived from the placebo responder subgroup; as shown by two-way analysis of variance (performance style, F = 4.30; p = 0.040; η² = 0.035; style × responder status interaction term, F = 5.21; p = 0.024) followed by post hoc analysis showing a ∼60% increase in pain threshold in responders exposed to scenario B (p = 0.020).

Conclusion: These results support the hypothesis that structured manipulation of physician’s verbal and non-verbal performance, designed to build rapport and increase faith in treatment, is feasible and may have a significant beneficial effect on the size of the response to placebo analgesia. They also demonstrate that subjects, who are not susceptible to placebo, are also not susceptible to performance style.

Early-life experiences and the development of adult diseases with a focus on mental illness: The Human Birth Theory

In mammals, early adverse experiences, including mother-pup interactions, shape the response of an individual to chronic stress or to stress-related diseases during adult life. This has led to the elaboration of the theory of the developmental origins of health and disease, in particular adult diseases such as cardiovascular and metabolic disorders. In addition, in humans, as stated by Massimo Fagioli's Human Birth Theory, birth is healthy and equal for all individuals, so that mental illness develop exclusively in the postnatal period because of the quality of the relationship in the first year of life. Thus, this review focuses on the importance of programming during the early developmental period on the manifestation of adult diseases in both animal models and humans. Considering the obvious differences between animals and humans we cannot systematically move from animal models to humans. Consequently, in the first part of this review, we will discuss how animal models can be used to dissect the influence of adverse events occurring during the prenatal and postnatal periods on the developmental trajectories of the offspring, and in the second part, we will discuss the role of postnatal critical periods on the development of mental diseases in humans. Epigenetic mechanisms that cause reversible modifications in gene expression, driving the development of a pathological phenotype in response to a negative early postnatal environment, may lie at the core of this programming, thereby providing potential new therapeutic targets. The concept of the Human Birth Theory leads to a comprehension of the mental illness as a pathology of the human relationship immediately after birth and during the first year of life.

Turning the Lens of Science on Itself: Verbal Overshadowing, Replication, and Metascience

This issue of Perspectives on Psychological Science reports an unprecedented replication effort entailing numerous independent laboratories conducting two versions of the verbal overshadowing paradigm (Schooler & Engstler-Schooler, 1990) using different timing intervals. The results (Alogna et al., 2014, this issue) provide unequivocal support for the existence of verbal overshadowing--the finding that describing a previously seen face can impair its subsequent recognition--while simultaneously revealing a number of factors that may have contributed to challenges in replicating verbal overshadowing in the past. In this commentary, I review my participation in this process and consider the implications of the results of this replication effort for verbal overshadowing, the decline effect, and the general goal of metascience: turning the lens of science onto itself.

Mechanisms of the placebo effect in pain and psychiatric disorders

Placebo effect research over the past 15 years has improved our understanding of how placebo treatments reduce patient symptoms. The expectation of symptom improvement is the primary factor underlying the placebo effect. Such expectations are shaped by past experiences, contextual cues and biological traits, which ultimately modulate one's degree of response to a placebo. The body of evidence that describes the physiology of the placebo effect has been derived from mechanistic studies primarily restricted to the setting of pain. Imaging findings support the role of endogenous opioid and dopaminergic networks in placebo analgesia in both healthy patients as well as patients with painful medical conditions. In patients with psychiatric illnesses such as anxiety disorders or depression, a vast overlap in neurological changes is observed in drug responders and placebo responders supporting the role of serotonergic networks in placebo response. Molecular techniques have been relatively underutilized in understanding the placebo effect until recently. We present an overview of the placebo responder phenotypes and genetic markers that have been associated with the placebo effect in pain, schizophrenia, anxiety disorders and depression.

Placebo Response in Repetitive Transcranial Magnetic Stimulation Trials of Treatment of Auditory Hallucinations in Schizophrenia: A Meta-Analysis

Several meta-analyses have assessed the response of patients with schizophrenia with auditory verbal hallucinations (AVH) to treatment with repetitive transcranial magnetic stimulation (rTMS); however, the placebo response has never been explored. Typically observed in a therapeutic trial, the placebo effect may have a major influence on the effectiveness of rTMS. The purpose of this meta-analysis is to evaluate the magnitude of the placebo effect observed in controlled studies of rTMS treatment of AVH, and to determine factors that can impact the magnitude of this placebo effect, such as study design considerations and the type of sham used.The study included twenty-one articles concerning 303 patients treated by sham rTMS. A meta-analytic method was applied to obtain a combined, weighted effect size, Hedges's g. The mean weighted effect size of the placebo effect across these 21 studies was 0.29 (P < .001). Comparison of the parallel and crossover studies revealed distinct results for each study design; placebo has a significant effect size in the 13 parallel studies (g = 0.44, P < 10(-4)), but not in the 8 crossover studies (g = 0.06, P = .52). In meta-analysis of the 13 parallel studies, the 45° position coil showed the highest effect size. Our results demonstrate that placebo effect should be considered a major source of bias in the assessment of rTMS efficacy. These results fundamentally inform the design of further controlled studies, particularly with respect to studies of rTMS treatment in psychiatry.

A double-blind, placebo-controlled, randomized withdrawal study of lurasidone for the maintenance of efficacy in patients with schizophrenia

OBJECTIVE

To evaluate the effectiveness of lurasidone as maintenance treatment for schizophrenia.

METHOD

Adults experiencing an acute exacerbation of schizophrenia initially received 12-24 weeks of open-label treatment with lurasidone (40-80 mg/d, flexibly dosed). Patients who maintained clinical stability for ⩾12 weeks were randomized in double-blind fashion to placebo or lurasidone (40-80 mg/d, flexibly dosed) for an additional 28-week treatment period. The primary efficacy endpoint was time to relapse (based on Kaplan-Meier survival analysis).

RESULTS

A total of 676 patients enrolled in the open-label phase; 285 met protocol-specified stabilization criteria and were randomized to lurasidone (N=144) or placebo (N=141). During the open-label phase, mean Positive and Negative Syndrome Scale total score decreased from 90.1 to 54.4 in patients who met clinical stability criteria and were randomized. In the double-blind phase, lurasidone significantly delayed time to relapse compared with placebo (log-rank test, p=0.039), reflecting a 33.7% reduction in risk of relapse (Cox hazard ratio (95% confidence interval), 0.663 (0.447-0.983); p=0.041). Probability of relapse at the double-blind week 28 endpoint (based on Kaplan-Meier analysis) was 42.2% in the lurasidone group and 51.2% in the placebo group. Minimal changes in weight, lipid, glucose, and prolactin were observed throughout the study.

CONCLUSIONS

This multicenter, placebo-controlled, randomized withdrawal study demonstrated the efficacy of lurasidone for the maintenance treatment of patients with schizophrenia.

Methodological issues associated with preclinical drug development and increased placebo effects in schizophrenia clinical trials

Recent failures to detect efficacy in clinical trials investigating pharmacological treatments for schizophrenia raise concerns regarding the potential contribution of methodological shortcomings to this research. This review provides an examination of two key methodological issues currently suspected of playing a role in hampering schizophrenia drug development; 1) limitations on the translational utility of preclinical development models, and 2) methodological challenges posed by increased placebo effects. Recommendations for strategies to address these methodological issues are addressed.

Age and sex as moderators of the placebo response – an evaluation of systematic reviews and meta-analyses across medicine

Predictors of the placebo response (PR) in randomized controlled trials (RCT) have been searched for ever since RCT have become the standard for testing novel therapies and age and gender are routinely documented data in all trials irrespective of the drug tested, its indication, and the primary and secondary end points chosen. To evaluate whether age and gender have been found to be reliable predictors of the PR across medical subspecialties, we extracted 75 systematic reviews, meta-analyses, and meta-regressions performed in major medical areas (neurology, psychiatry, internal medicine) known for high PR rates. The literature database used contains approximately 2,500 papers on various aspects of the genuine PR. These ‘meta-analyses’ were screened for statistical predictors of the PR across multiple RCT, including age and gender, but also other patient-based and design-based predictors of higher PR rates. Retrieved papers were sorted for areas and disease categories. Only 15 of the 75 analyses noted an effect of younger age to be associated with higher PR, and this was predominantly in psychiatric conditions but not in depression, and internal medicine but not in gastroenterology. Female gender was associated with higher PR in only 3 analyses. Among the patient-based predictors, the most frequently noted factor was lower symptom severity at baseline, and among the design- based factors, it was a randomization ratio that selected more patients to drugs than to placebo, more frequent study visits, and more recent trials that were associated with higher PR rates. While younger age may contribute to the PR in some conditions, sex does not. There is currently no evidence that the PR is different in the elderly. PR are, however, markedly influenced by the symptom severity at baseline, and by the likelihood of receiving active treatment in placebo- controlled trials.

No evidence of a control group response in exercise randomised controlled trials in people with schizophrenia: A systematic review and meta-analysis

Increased control group responses (CGR) make it more difficult to establish the effectiveness of interventions to improve symptoms in schizophrenia. We conducted a meta-analysis of CGR within randomised control trials (RCTs) comparing exercise and a control condition in people with schizophrenia. We found no evidence of a CGR for total, positive or negative symptoms. Control group responses do not negatively impact exercise RCTs that have clearly demonstrated substantial beneficial effects of exercise in this population.

Medication Nonadherence, "Professional Subjects," and Apparent Placebo Responders: Overlapping Challenges for Medications Development

Nonadherence is a major problem in clinical trials of new medications. To evaluate the extent of nonadherence, this study evaluated pharmacokinetic sampling from 1765 subjects receiving active therapy across 8 psychiatric trials conducted between 2001 and 2011. With nonadherence defined as greater than 50% of plasma samples below the limit of quantification for study drug, the percentage of nonadherent subjects ranged from 12.8% to 39.2%. There was a trend toward increased nonadherence in studies with greater numbers of subjects, but an association with nonadherence was not apparent for other study design parameters or subject characteristics. For 2 trials with multiple recruitment sites in geographical proximity, several subjects attempted to simultaneously enroll at separate site locations. The construct of "professional subjects," those who enroll in trials only for financial gain, is gaining attention, and we therefore modeled the impact of professional subjects on medication efficacy trials. The results indicate that enrollment of professional subjects who are destined to succeed (those who will appear to achieve treatment success regardless of study drug assignment) can substantially increase both the apparent placebo response rate and the sample size requirement for statistical power, while decreasing the observed effect size. The overlapping nature of nonadherence, professional subjects, and placebo response suggests that these issues should be considered and addressed together. Following this approach, we describe a novel clinical trial design to minimize the adverse effects of professional subjects on trial outcomes and discuss methods to monitor adherence.

Placebo effects and their determinants in gastrointestinal disorders

Placebo effects in clinical trials have sparked an interest in the placebo phenomenon, both in randomized controlled trials (RCTs) and in experimental gastroenterology. RCTs have demonstrated similar short-term and long-term placebo response rates in gastrointestinal compared to other medical diagnoses. Most mediators and moderators of placebo effects in gastrointestinal diseases are also of similar type and size to other medical diagnoses and not specific for gastrointestinal diagnoses. Other characteristics such as an increase in the placebo response over time and the placebo-enhancing effects of unbalanced randomization were not seen, at least in IBS. Experimental placebo and nocebo studies underscore the 'power' of expectancies and conditioning processes in shaping gastrointestinal symptoms not only at the level of self-reports, but also within the brain and along the brain-gut axis. Brain imaging studies have redressed earlier criticism that placebo effects might merely reflect a response bias. These findings raise hope that sophisticated trials and experiments designed to boost positive expectations and minimize negative expectations could pave the way for a practical and ethically sound use of placebo knowledge in daily practice. Rather than focusing on a 'personalized' choice of drugs based on biomarkers or genes, it might be the doctor-patient communication that needs to be tailored.

Placebo response in antipsychotic trials of patients with acute mania: Results of an individual patient data meta-analysis

We examined the role of placebo response in acute mania trials. Specifically, whether placebo response: (1) predicts treatment effect, (2) can be predicted by patient and study characteristics, and (3) can be predicted by a parsimonious model. We performed a meta-analysis of individual patient data from 10 registration studies (n=1019) for the indication acute manic episode of bipolar disorder. We assessed the effect of 14 determinants on placebo response. Primary outcome measures were mean symptom change score (MCS) on the Young Mania Rating Scale (YMRS) and response rate (RR), defined as ≥ 50% YMRS symptom improvement from baseline to endpoint. The overall placebo response was 8.5 points improvement on the YMRS (=27.9%) with a RR of 32.8%. Placebo response was significantly associated with the overall treatment response. Five determinants significantly (p<0.05) predicted the placebo response. The multivariate prediction model, which consisted of baseline severity, psychotic features at baseline, number of geographic regions, and region, explained 10.4% and 5.5% of the variance in MSC and RR, respectively. Our findings showed that the placebo response in efficacy trials of antipsychotics for acute mania is substantial and an important determinant of treatment effect. Placebo response is influenced by patient characteristics (illness severity and presence of psychotic features) and by study characteristics (study year, number of geographic regions and region). However, the prediction model could only explain the placebo response to a limited extent. Therefore, limiting trials to certain patients in certain geographic regions seems not a viable strategy to improve assay sensitivity.

Increasing placebo response in antipsychotic trials: a clinical perspective

An increase in placebo response is often cited as rationale for the continuously diminishing drug-placebo differences in randomized controlled trials (RCTs) evaluating antipsychotic and antidepressant drugs. As a consequence, the probability for negative study results in placebo-controlled RCTs grows. This alarming trend conveys the impression that the newer marked psychopharmacological medications are less efficacious compared to the older ones although particularly trial methodological reasons contribute to the mitigation of the drug-placebo contrasts over the last decades. With regard to antipsychotic RCTs, the present article aims to elucidate the magnitude of the raising placebo response, factors contributing to this increase, and potential reasons for this phenomenon. Therefore, we summarize and critically discuss the findings of two recent meta-analyses on this topic. Both research projects revealed that the mean improvement of schizophrenic symptoms in the placebo groups of antipsychotic trials increased considerably over time. Factors that were significantly associated with larger placebo response in antipsychotic trials comprise with respect to participants characteristics younger age and shorter duration of illness. The results in terms of symptom severity at baseline were conflictive. In terms of trial methodology factors, shorter study duration, a larger number of study sites and participants, fewer academic/university sites, and a lower percentage of patients randomized to placebo were identified as potential predictors for high placebo response. The implications of these findings for the interpretation of antipsychotic trial results and meta-analyses are presented.

Placebo eff ects in psychiatry: mediators and moderators

A strong placebo response in psychiatric disorders has been noted for the past 50 years and various attempts have been made to identify predictors of it, by use of meta-analyses of randomised controlled trials and laboratory studies. We reviewed 31 meta-analyses and systematic reviews of more than 500 randomised placebo-controlled trials across psychiatry (depression, schizophrenia, mania, attention-deficit hyperactivity disorder, autism, psychosis, binge-eating disorder, and addiction) for factors identified to be associated with increased placebo response. Of 20 factors discussed, only three were often linked to high placebo responses: low baseline severity of symptoms, more recent trials, and unbalanced randomisation (more patients randomly assigned to drug than placebo). Randomised controlled trials in non-drug therapy have not added further predictors, and laboratory studies with psychological, brain, and genetic approaches have not been successful in identifying predictors of placebo responses. This comprehensive Review suggests that predictors of the placebo response are still to be discovered, the response probably has more than one mediator, and that different and distinct moderators are probably what cause the placebo response within psychiatry and beyond.