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

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.

The Placebo Effect in Psychosis: Why It Matters and How to Measure It

Psychosis is characterized by unusual percepts and beliefs in the form of hallucinations and delusions. Antipsychotic medication, the primary treatment for psychosis, is often ineffective and accompanied by severe side effects, but research has not identified an effective alternative in several decades. One reason that clinical trials fail is that patients with psychosis tend to show a significant therapeutic response to inert control treatments, known as the placebo effect, which makes it difficult to distinguish drug effects from placebo effects. Conversely, in clinical practice, a strong placebo effect may be useful because it could enhance the overall treatment response. Identifying factors that predict large placebo effects could improve the future outlook of psychosis treatment. Biomarkers of the placebo effect have already been suggested in pain and depression, but not in psychosis. Quantifying markers of the placebo effect would have the potential to predict placebo effects in psychosis clinical trials. Furthermore, the placebo effect and psychosis may represent a shared neurocognitive mechanism in which prior beliefs are weighted against new sensory information to make inferences about reality. Examining this overlap could reveal new insights into the mechanisms underlying psychosis and indicate novel treatment targets. We provide a narrative review of the importance of the placebo effect in psychosis and propose a novel method to assess it.

Placebo response of sham acupuncture in patients with primary dysmenorrhea: A meta-analysis

BACKGROUND

The placebo response of sham acupuncture in patients with primary dysmenorrhea is a substantial factor associated with analgesia. However, the magnitude of the placebo response is unclear.

OBJECTIVE

This meta-analysis assessed the effects of sham acupuncture in patients with primary dysmenorrhea and the factors contributing to these effects.

SEARCH STRATEGY

PubMed, Embase, Web of Science, and Cochrane CENTRAL databases were searched from inception up to August 20, 2022.

INCLUSION CRITERIA

Randomized controlled trials (RCTs) using sham acupuncture as a control for female patients of reproductive age with primary dysmenorrhea were included.

DATA EXTRACTION AND ANALYSIS

Pain intensity, retrospective symptom scale, and health-related quality of life were outcome measures used in these trials. Placebo response was defined as the change in the outcome of interest from baseline to endpoint. We used standardized mean difference (SMD) to estimate the effect size of the placebo response.

RESULTS

Thirteen RCTs were included. The pooled placebo response size for pain intensity was the largest (SMD = -0.99; 95% confidence interval [CI], -1.31 to -0.68), followed by the retrospective symptom scale (Total frequency rating score: SMD = -0.20; 95% CI, -0.80 to -0.39. Average severity score: SMD = -0.35; 95% CI, -0.90 to -0.20) and physical component of SF-36 (SMD = 0.27; 95% CI, -0.17 to 0.72). Studies using blunt-tip needles, single-center trials, studies with a low risk of bias, studies in which patients had a longer disease course, studies in which clinicians had < 5 years of experience, and trials conducted outside Asia were more likely to have a lower placebo response.

CONCLUSION

Strong placebo response and some relative factors were found in patients with primary dysmenorrhea. PROSPERO registration number: CRD42022304215. Please cite this article as: Sun CY, Xiong ZY, Sun CY, Ma PH, Liu XY, Sun CY, Xin ZY, Liu BY, Liu CZ, Yan SY. Placebo response of sham acupuncture in patients with primary dysmenorrhea: A meta-analysis. J Integr Med. 2023; 21(5): 455-463.

Predictors of placebo response in three large clinical trials of the V1a receptor antagonist balovaptan in autism spectrum disorder

High rates of placebo response are increasingly implicated in failed autism spectrum disorder (ASD) clinical trials. Despite this, there are limited investigations of placebo response in ASD. We sought to identify baseline predictors of placebo response and quantify their influence on clinical scales of interest for three harmonized randomized clinical trials of balovaptan, a V1a receptor antagonist. We employed a two-step approach to identify predictors of placebo response on the Vineland-II two-domain composite (2DC) (primary outcome and a caregiver measure) and Clinical Global Impression (CGI) scale (secondary outcome and a clinician measure). The initial candidate predictor set of variables pertained to participant-level, site-specific, and protocol-related factors. Step 1 aimed to identify influential predictors of placebo response using Least Absolute Shrinkage and Selection Operator (LASSO) regression, while Step 2 quantified the influence of predictors via linear regression. Results were validated through statistical bootstrapping approaches with 500 replications of the analysis dataset. The pooled participant-level dataset included individuals with ASD aged 5 to 62 years (mean age 21 [SD 10]), among which 263 and 172 participants received placebo at Weeks 12 and 24, respectively. Although no influential predictors were identified for CGI, findings for Vineland-II 2DC are robust and informative. Decreased placebo response was predicted by higher baseline Vineland-II 2DC (i.e., more advanced adaptive function), longer trial duration, and European (vs United States) sites, while increased placebo response was predicted by commercial (vs academic) sites, attention deficit hyperactivity disorder and depression. Identification of these factors may be useful in anticipating and mitigating placebo response in drug development efforts in ASD and across developmental and psychiatric conditions.

Feasibility of intermediate theta burst stimulation as sham control in therapeutic transcranial magnetic stimulation studies

A major challenge in Transcranial Magnetic Stimulation trials is that of an inefficient sham protocol. This could potentially amplify the gap in behavioral outcomes following true and control treatments. Intermediate theta-burst stimulation (imTBS) is a promising sham alternative since it uses actual TMS pulses, thus mimicking the sensory effects of stimulation without producing physiological aftereffects. Here, we critically review controlled experiments that have examined physiological and behavioral aftereffects following imTBS with the intention to further investigate what appears to be a promising sham control modality for TBS studies.

Zavegepant nasal spray for the acute treatment of migraine: A Phase 2/3 double-blind, randomized, placebo-controlled, dose-ranging trial

OBJECTIVE

Evaluate the efficacy, safety, and tolerability of zavegepant nasal spray in the acute treatment of migraine.

BACKGROUND

Calcitonin gene-related peptide-targeting agents are a novel class of therapeutics for migraine, but none are currently available as a nonoral option for acute treatment. Zavegepant, a high-affinity, selective, and structurally unique calcitonin gene-related peptide-receptor antagonist in late-stage development, is formulated as a nasal spray for the acute treatment of migraine.

METHODS

This randomized, dose-ranging, placebo-controlled, Phase 2/3 trial in adults aged ≥18 years with migraine (NCT03872453) was conducted at US study sites. Participants were randomized by an interactive web response system and treated a single attack of moderate to severe pain intensity with zavegepant nasal spray 5, 10, 20 mg, or placebo. Coprimary efficacy endpoints were pain freedom and freedom from the most bothersome symptom at 2 h postdose.

RESULTS

Of the 1673 participants aged 18 to 79 years who were randomized, 1588 were treated with study medication, and 1581 (mean age 40.8 years, 85.5% female) were analyzed for efficacy: zavegepant 5 mg (n = 387), 10 mg (n = 391), 20 mg (n = 402), and placebo (n = 401). Zavegepant 10 and 20 mg were more effective than placebo on the coprimary endpoints of pain freedom at 2 h postdose (placebo: 15.5% [98.3% confidence interval (CI), 11.1, 19.8]; 10 mg: 22.5% [98.3% CI, 17.5, 27.6; p = 0.0113]; 20 mg: 23.1% [98.3% CI, 18.1, 28.2; p = 0.0055]) and freedom from the most bothersome symptom at 2 h postdose (placebo: 33.7% [98.3% CI, 28.0, 39.3]; 10 mg: 41.9% [98.3% CI, 36.0, 47.9; p = 0.0155]; 20 mg: 42.5% [98.3% CI, 36.6, 48.4; p = 0.0094]). Findings for the 5 mg dose were not significant. The most common treatment-emergent adverse events with zavegepant 10 and 20 mg and placebo were dysgeusia (13.5% to 16.1% vs. 3.5%), nausea (2.7% to 4.1% vs. 0.5%), and nasal discomfort (1.3% to 5.2% vs. 0.2%). Most adverse events were mild or moderate and resolved without treatment. There was no signal of hepatotoxicity.

CONCLUSION

Zavegepant nasal spray, in single doses of 10 or 20 mg, was effective for the acute treatment of migraine, with a favorable safety profile. Additional research is needed to confirm its potential as a nonoral medication for the acute treatment of migraine.

Evidence for stratified conflicts of interest policies in research contexts: a methodological review

OBJECTIVES

The purpose of this study was to conduct a methodological review of research on the effects of conflicts of interest (COIs) in research contexts.

DESIGN

Methodological review.

DATA SOURCES

Ovid.

ELIGIBILITY CRITERIA

Studies published between 1986 and 2021 conducting quantitative assessments of relationships between industry funding or COI and four target outcomes: positive study results, methodological biases, reporting quality and results-conclusions concordance.

DATA EXTRACTION AND SYNTHESIS

We assessed key facets of study design: our primary analysis identified whether studies stratified industry funding or COI variables by magnitude (ie, number of COI or disbursement amount), type (employment, travel fees, speaking fees) or if they assessed dichotomous variables (ie, conflict present or absent). Secondary analyses focused on target outcomes and available effects measures.

RESULTS

Of the 167 articles included in this study, a substantial majority (98.2%) evaluated the effects of industry sponsorship. None evaluated associations between funding magnitude and outcomes of interest. Seven studies (4.3%) stratified industry funding based on the mechanism of disbursement or funder relationship to product (manufacturer or competitor). A fifth of the articles (19.8%) assessed the effects of author COI on target outcomes. None evaluated COI magnitude, and three studies (9.1%) stratified COI by disbursement type and/or reporting practices. Participation of an industry-employed author showed the most consistent effect on favourability of results across studies.

CONCLUSIONS

Substantial evidence demonstrates that industry funding and COI can bias biomedical research. Evidence-based policies are essential for mitigating the risks associated with COI. Although most policies stratify guidelines for managing COI, differentiating COIs based on the type of relationship or monetary value, this review shows that the available research has generally not been designed to assess the differential risks of COI types or magnitudes. Targeted research is necessary to establish an evidence base that can effectively inform policy to manage COI.

Effect of Treatment Adherence Improvement Program in Hemodialysis Patients: A Systematic Review and Meta-Analysis

Herein, we performed a meta-analysis evaluating the effects of treatment adherence enhancement programs on treatment adherence and secondary outcomes for hemodialysis patients. Twenty-five Korean and international articles published prior to 31 March 2022 were selected following the PRISMA and Cochrane Systematic Review guidelines. We calculated summary effect sizes, conducted homogeneity and heterogeneity testing, constructed a funnel plot, and performed Egger's regression test, Begg's test, trim-and-fill method, subgroup analyses, and univariate meta-regression. The overall effect of treatment adherence enhancement programs for hemodialysis patients was statistically significant (Hedges' g = 1.10, 95% CI: 0.77, 1.43). On performing subgroup analysis to determine the cause of effect size heterogeneity, statistically significant moderating effects were found for a range of input variables (Asian countries, study centers, sample size, study design, intervention types, number of sessions, quality assessment scores, funding, and evidence-based interventions). On univariate meta-regression, larger synthesized effect sizes were found for a range of study characteristics (Asian populations, single-center studies, studies with <70 participants, quasi-experimental studies, educational interventions, studies with >12 sessions, studies with quality assessment scores above the mean, unfunded studies, and non-theory-based interventions). Our results provide evidence-based information for enhancing program efficacy when designing treatment adherence enhancement programs for hemodialysis patients.

Systematic review and meta-analysis of the placebo effect in panic disorder: Implications for research and clinical practice

OBJECTIVE

This review aimed to measure the degree of placebo response in panic disorder.

DATA SOURCES

We searched major databases up to 31 January 2021, for randomized pharmacotherapy trials published in English.

STUDY SELECTION

A total of 43 studies met inclusion criteria to be in the analysis (with 174 separate outcome measurements).

DATA EXTRACTION

Changes in outcome measures from baseline in the placebo group were used to estimate modified Cohen's d effect size.

RESULTS

A total of 43 trials (2392 subjects, 174 outcomes using 27 rating scales) were included in the meta-analysis. Overall placebo effect size was 0.57 (95% confidence interval = [0.50, 0.64]), heterogeneity (I²: 96.3%). Higher placebo effect size was observed among clinician-rated scales compared to patient reports (0.75 vs 0.35) and among general symptom and anxiety scales compared to panic symptoms and depression scales (0.92 and 0.64 vs 0.56 and 0.54, respectively). There was an upward trend in effect size over the publication period (r = 0.02, p = 0.002) that was only significant among clinician-rated scales (r = 0.02, p = 0.011). There was no significant publication bias, Egger's test (p = 0.08).

CONCLUSION

We observed a substantial placebo effect size in panic disorder. This effect was more prominent for some aspects of panic disorder psychopathology than for others and was correlated with the source of the assessment and publication year. This finding has implications both for research design, to address the heterogeneity and diversity in placebo responses, and for clinical practice to ensure optimal quality of care.

SYSTEMATIC REVIEW REGISTRATION NUMBER

PROSPERO, CRD42019125979.

A double-blind, randomized, placebo-controlled proof of concept study of the efficacy and safety of Lu AF11167 for persistent negative symptoms in people with schizophrenia

Lu AF11167 is a selective, high-affinity inhibitor of PDE10A that modulates dopamine D1 and D2 receptor-mediated intraneuronal signalling without binding to these receptors. This randomized, double-blind, parallel-group, placebo-controlled study (NCT03793712) with open-label extension (NCT03929497) evaluated the efficacy of two fixed-flexible doses (1-2mg/day and 3-4mg/day) of Lu AF11167 in stable, non-acute patients with schizophrenia and persistent prominent negative symptoms. The studies were discontinued following a futility analysis of the double-blind study, and we report data collected up to study termination. Of the 210 patients screened, 162 were randomized, 111 completed the double-blind study and 96 entered the open-label study before early termination. The withdrawal rate due to impending relapse was low and comparable across treatment groups (n = 2-4 per group in the double-blind study and n = 1 in the open-label extension). Double-blind treatment with Lu AF11167 3-4mg was not superior to placebo in the reduction of Brief Negative Symptom Scale (BNSS) total scores from Baseline to Week 12 (primary endpoint); adjusted mean changes were -6.8 with placebo, -5.7 with Lu AF11167 1-2 mg group and -6.0 with Lu AF11167 3-4mg. Treatment with Lu AF11167 1-2mg also failed to separate from placebo on the primary endpoint. Neither dose group showed significant improvements versus placebo on any of the secondary efficacy measures exploring effect of treatment on overall symptomology, negative symptoms, positive symptoms, or functioning. Administration of Lu AF11167 was safe and well tolerated and adverse events were not a major reason for withdrawal from the study.

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.

Large multicenter randomized trials in autism: key insights gained from the balovaptan clinical development program

BACKGROUND

Autism spectrum disorder (ASD) is a common and heterogeneous neurodevelopmental condition that is characterized by the core symptoms of social communication difficulties and restricted and repetitive behaviors. At present, there is an unmet medical need for therapies to ameliorate these core symptoms in order to improve quality of life of autistic individuals. However, several challenges are currently faced by the ASD community relating to the development of pharmacotherapies, namely in the conduct of clinical trials. Balovaptan is a V1a receptor antagonist that has been investigated to improve social communication difficulties in individuals with ASD. In this viewpoint, we draw upon our recent first-hand experiences of the balovaptan clinical development program to describe current challenges of ASD trials.

DISCUSSION POINTS

The balovaptan trials were conducted in a wide age range of individuals with ASD with the added complexities associated with international trials. When summarizing all three randomized trials of balovaptan, a placebo response was observed across several outcome measures. Placebo response was predicted by greater baseline symptom severity, online recruitment of participants, and less experienced or non-academic trial sites. We also highlight challenges relating to selection of outcome measures in ASD, the impact of baseline characteristics, and the role of expectation bias in influencing trial results.

CONCLUSION

Taken together, the balovaptan clinical development program has advanced our understanding of the key challenges facing ASD treatment research. The insights gained can be used to inform and improve the design of future clinical trials with the collective aim of developing efficacious therapies to support individuals with ASD.

Effect of disease related biases on the subjective assessment of social functioning in Alzheimer's disease and schizophrenia patients

BACKGROUND

Questionnaires are the current hallmark for quantifying social functioning in human clinical research. In this study, we compared self- and proxy-rated (caregiver and researcher) assessments of social functioning in Schizophrenia (SZ) and Alzheimer's disease (AD) patients and evaluated if the discrepancy between the two assessments is mediated by disease-related factors such as symptom severity.

METHODS

We selected five items from the WHO Disability Assessment Schedule 2.0 (WHODAS) to assess social functioning in 53 AD and 61 SZ patients. Caregiver- and researcher-rated assessments of social functioning were used to calculate the discrepancies between self-rated and proxy-rated assessments. Furthermore, we used the number of communication events via smartphones to compare the questionnaire outcomes with an objective measure of social behaviour.

RESULTS

WHODAS results revealed that both AD (p < 0.001) and SZ (p < 0.004) patients significantly overestimate their social functioning relative to the assessment of their caregivers and/or researchers. This overestimation is mediated by the severity of cognitive impairments (MMSE; p = 0.019) in AD, and negative symptoms (PANSS; p = 0.028) in SZ. Subsequently, we showed that the proxy scores correlated more strongly with the smartphone communication events of the patient when compared to the patient-rated questionnaire scores (self; p = 0.076, caregiver; p < 0.001, researcher-rated; p = 0.046).

CONCLUSION

Here we show that the observed overestimation of WHODAS social functioning scores in AD and SZ patients is partly driven by disease-related biases such as cognitive impairments and negative symptoms, respectively. Therefore, we postulate the development and implementation of objective measures of social functioning that may be less susceptible to such biases.

Pimavanserin for negative symptoms of schizophrenia: results from the ADVANCE phase 2 randomised, placebo-controlled trial in North America and Europe

BACKGROUND

Negative symptoms of schizophrenia are associated with adverse clinical outcomes, but there are few effective treatments. We aimed to assess the effects of pimavanserin, a selective 5-HT_2A inverse agonist and antagonist, on negative symptoms of schizophrenia.

METHODS

The ADVANCE study was a phase 2, 26-week, randomised, double-blind, placebo-controlled study of pimavanserin in stable outpatients with schizophrenia aged 18-55 years with predominant negative symptoms. Patients were randomly assigned (1:1) across 83 sites (18 in North America and 65 in Europe) to receive pimavanserin or placebo daily, added to an ongoing antipsychotic medication, per a computer-generated schedule (stratification by geographical region). Eligible patients had a score of at least 20 on the sum of seven Positive and Negative Syndrome Scale (PANSS) Marder negative factor items (and scores of ≥4 on at least three or ≥5 on at least two of negative symptom items). The starting dosage of 20 mg of pimavanserin or placebo could be adjusted to 34 mg or 10 mg within the first 8 weeks of the study, after which dosage remained stable until the end of the study. Both pimavanserin and placebo were administered orally once daily as two individual tablets (pimavanserin tablets were either 10 mg or 17 mg). The primary endpoint was change in total score using the 16-item Negative Symptom Assessment (NSA-16) from baseline to week 26. Primary outcomes were analysed in patients who received at least one dose of the study drug and had NSA-16 assessments at baseline and at least once post-baseline (full analysis set). Safety outcomes were analysed in patients who had received at least one dose of the study drug. This trial is registered with ClinicalTrials.gov, NCT02970305, and is complete.

FINDINGS

Between Nov 4, 2016, and April 16, 2019, we randomly assigned 403 patients to pimavanserin (n=201; 131 [65%] male; 187 [93%] White) or placebo (n=202; 137 [68%] male, 186 (92%) White), of whom 400 were included in the efficacy analysis (199 in the pimavanserin group, 201 in the placebo group). Mean age was 37·7 years (SD 9·4) in the pimavanserin group and 36·7 (9·2) years in the placebo group. The change in total NSA-16 score from baseline to week 26 was significantly improved with pimavanserin (least squares mean -10·4 [SE 0·67]) versus placebo (least squares mean -8·5 [0·67]; p=0·043; effect size: 0·211). The number of patients with treatment-emergent adverse events (TEAEs) was similar between groups: 80 (40%) patients experienced TEAEs in the pimavanserin group and 71 (35%) in the placebo group. Most TEAEs were headache (6% [n=13] vs 5% [n=10]) and somnolence (5% [n=11] vs 5% [n=10]). One patient from the placebo group reported severe headache (0·5%), rhinorrhoea (0·5%), cough (0·5%), and influenza (0·5%). In the pimavanserin group, one patient reported severe toothache (0·5%), and two patients had worsening of schizophrenia (1%). Mean change in QTcF interval was higher with pimavanerin (4·5 ms [SD 18·0]) than with placebo (0·0 ms [16·0]).

INTERPRETATION

Stable patients with predominant negative symptoms of schizophrenia showed a reduction in negative symptoms after treatment with pimavanserin. However, given the small effect size, further investigation with optimised dosing is warranted to determine the clinical significance of this effect.

FUNDING

Acadia Pharmaceuticals.

Magnitude of the Placebo Response Across Treatment Modalities Used for Treatment-Resistant Depression in Adults: A Systematic Review and Meta-analysis

IMPORTANCE

The placebo effect in depression clinical trials is a substantial factor associated with failure to establish efficacy of novel and repurposed treatments. However, the magnitude of the placebo effect and whether it differs across treatment modalities in treatment-resistant depression (TRD) is unclear.

OBJECTIVE

To examine the magnitude of the placebo effect in patients with TRD across different treatment modalities and its possible moderators.

DATA SOURCES

Searches were conducted on MEDLINE, Web of Science, and PsychInfo from inception to June 21, 2021.

STUDY SELECTION

Randomized clinical trials (RCTs) were included if they recruited patients with TRD and randomized them to a placebo or sham arm and a pharmacotherapy, brain stimulation, or psychotherapy arm.

DATA EXTRACTION AND SYNTHESIS

Independent reviewers used standard forms for data extraction and quality assessment. Random-effects analyses and standard pairwise meta-analyses were performed.

MAIN OUTCOMES AND MEASURES

The primary outcome was the Hedges g value for the reported depression scales. Secondary outcomes included moderators assessed via meta-regression and response and remission rates. Heterogeneity was assessed with the I2 test, and publication bias was evaluated using the Egger test and a funnel plot. Cochrane Risk of Bias Tool was used to estimate risks.

RESULTS

Fifty RCTs were included involving various types of placebo or sham interventions with a total of 3228 participants (mean [SD] age, 45.8 [6.0] years; 1769 [54.8%] female). The pooled placebo effect size for all modalities was large (g = 1.05; 95% CI, 0.91-1.1); the placebo effect size in RCTs of specific treatment modalities did not significantly differ. Similarly, response and remission rates associated with placebo were comparable across modalities. Heterogeneity was large. Three variables were associated with a larger placebo effect size: open-label prospective treatment before double-blind placebo randomization (β = 0.35; 95% CI, 0.11 to 0.59; P = .004), later year of publication (β = 0.03; 95% CI, 0.003 to 0.05; P = .03), and industry-sponsored trials (β = 0.34; 95% CI, 0.09 to 0.58; P = .007). The number of failed interventions was associated with the probability a smaller placebo effect size (β = -0.12; 95% CI, -0.23 to -0.01, P = .03). The Egger test result was not significant for small studies' effects.

CONCLUSIONS AND RELEVANCE

This analysis may provide a benchmark for past and future clinical RCTs that recruit patients with TRD standardizing an expected placebo effect size.

Placebo Response and Its Predictors in Attention Deficit Hyperactivity Disorder: A Meta-Analysis and Comparison of Meta-Regression and MetaForest

BACKGROUND

High placebo response in attention deficit hyperactivity disorder (ADHD) can reduce medication-placebo differences, jeopardizing the development of new medicines. This research aims to (1) determine placebo response in ADHD, (2) compare the accuracy of meta-regression and MetaForest in predicting placebo response, and (3) determine the covariates associated with placebo response.

METHODS

A systematic review with meta-analysis of randomized, placebo-controlled clinical trial investigating pharmacological interventions for ADHD was performed. Placebo response was defined as the change from baseline in ADHD symptom severity assessed according to the 18-item, clinician-rated, DSM-based rating scale. The effect of study design-, intervention-, and patient-related covariates in predicting placebo response was studied by means of meta-regression and MetaForest.

RESULTS

Ninety-four studies including 6614 patients randomized to placebo were analyzed. Overall, placebo response was -8.9 points, representing a 23.1% reduction in the severity of ADHD symptoms. Cross-validated accuracy metrics for meta-regression were R2 = 0.0012 and root mean squared error = 3.3219 for meta-regression and 0.0382 and 3.2599 for MetaForest. Placebo response among ADHD patients increased by 63% between 2001 and 2020 and was larger in the United States than in other regions of the world.

CONCLUSIONS

Strong placebo response was found in ADHD patients. Both meta-regression and MetaForest showed poor performance in predicting placebo response. ADHD symptom improvement with placebo has markedly increased over the last 2 decades and is greater in the United States than the rest of the world.