A Systematic Review of Study Design and Placebo Controls in Psychedelic Research

Modifying Informed Consent to Help Address Functional Unmasking in Psychedelic Clinical Trials

Importance

There is unprecedented clinician, industry, and patient interest in the therapeutic development of psychedelic drugs. This is due to a combination of promising clinical trial results, positive media coverage, and the lack of novel pharmacologic treatments for psychiatric disorders in recent decades. However, the field faces a key methodological challenge: masking participants to treatment conditions in psychedelic clinical trials has been largely unsuccessful.

Objective

When participants can tell whether they received active drug or placebo, their responses to clinical assessments, questionnaires, and even their functional imaging and biological data can be influenced by preconceptions about treatment effects. Positive patient expectancies combined with ineffective masking may skew outcomes and inflate effect sizes. This complicates efforts to determine the safety and efficacy of psychedelic drugs. Here, we explore a method to help address this problem: modifying informed consent to obscure information about the study design.

Evidence Review

We reviewed all contemporary (2000-2024) clinical trials of psychedelic or methylenedioxymethamphetamine (MDMA) therapy and corresponded with the investigators to compile information on the use of modifications to informed consent in these studies.

Findings

Modifying informed consent to obscure details of the study design has been implemented in several psychedelic clinical trials and may offer a way to strengthen masking. However, this approach poses significant ethical risks. We examine examples of modifications used in the psychedelic literature, discuss the current regulatory landscape, and suggest strategies to mitigate risks associated with modified informed consent.

Conclusions and Relevance

Incorporating modified informed consent in future psychedelic clinical trials may improve interpretability and impact, but this has not been explicitly tested. Modifications to informed consent may not be appropriate in all cases, and risks to participants should be minimized by implementing appropriate guardrails.

Reconsidering evidence for psychedelic-induced psychosis: an overview of reviews, a systematic review, and meta-analysis of human studies

BACKGROUND

Persons with schizophrenia are excluded from psychedelic-assisted therapy due to concerns about the risk of triggering or worsening psychosis. However, there is limited meta-analytic data on the risk of psychedelic-induced psychosis in individuals with pre-existing psychotic disorders.

METHODS

We conducted a systematic review, meta-analysis, and overview of reviews to assess the incidence of psychedelic-induced psychosis and symptom exacerbation in schizophrenia. Our pre-registered protocol (CRD42023399591) covered: LSD, psilocybin, mescaline, DMT, and MDMA, using data from Embase, PubMed, PsyARTICLES, PsyINFO, and trial registries up to November 2023. A random-effects model was used to calculate psychosis incidence, with standardized assessments of study quality.

RESULTS

From 131 publications, we analyzed 14 systematic reviews, 20 reviews, 35 randomized-controlled trials (RCTs), 10 case-control studies, 30 uncontrolled trials (UCTs), and 22 cohort studies, most of which were low quality. Meta-analysis of nine studies showed an incidence of psychedelic-induced psychosis at 0.002% in population studies, 0.2% in UCTs, and 0.6% in RCTs. In UCTs including individuals with schizophrenia, 3.8% developed long-lasting psychotic symptoms. Of those with psychedelic-induced psychosis, 13.1% later developed schizophrenia. Sensitivity analyses confirmed the results.

CONCLUSION

In summary, the reviewed evidence suggests that schizophrenia might not be a definite exclusion criterion for clinical trials exploring safety and efficacy of psychedelics for treatment-resistant depression and negative symptoms. However, given the low quality and limited number of studies, more high-quality research is needed, and a conservative approach is recommended until further data is available.

Efficacy and safety of psilocybin in the treatment of Major Depressive Disorder (MDD): A dose-response network meta-analysis of randomized placebo-controlled clinical trials

Selecting the optimal dose of psilocybin for treating Major Depressive Disorder (MDD) and Treatment-Resistant Depression (TRD) is crucial for clinical development and regulatory approval. This meta-analysis evaluates psilocybin's efficacy and safety in treating MDD to determine the optimal dose and timing for clinical trials. A systematic review and Dose-Response Network Meta-Analysis (NMA) of Randomized Placebo-Controlled Clinical Trials (RCTs) registered with PROSPERO was conducted. Databases searched included Embase, PubMed, Cochrane Library, Scopus, Web of Science, and Google Scholar, up to July 2024. The PICOS framework defined eligibility criteria: P: adult patients with MDD; I: psilocybin; C: placebo; O: changes in MADRS scores at Days 2, 8 and 15, and adverse events; S: RCT. Independent researchers performed data extraction and bias assessment. From 5419 search results, three RCTs involving 389 patients were included. Psilocybin significantly reduced symptoms compared to placebo at Day 8 (MD = -7.42; 95 % CI:10.07 to -4.78; p < 0.001) and Day 15 (MD = -9.55; 95 % CI:12.44 to -6.65; p < 0.001), without significant effects on Day 2. The NMA indicated that a 25 mg dose was the most effective, with a SUCRA value of 92.25 %, compared to doses of 0.215 mg/kg and 10 mg. However, psilocybin was associated with a higher risk of adverse events, particularly nausea (RR = 8.35; p < 0.001). This meta-analysis supports psilocybin's efficacy in treating MDD, particularly at a 25 mg dose, showing a time-dependent therapeutic effect. The recommended timing of efficacy evaluation by regulatory authorities is validated by this evidence, underscoring its importance in clinical trial design for psychedelic substances.

From relaxed beliefs under psychedelics (REBUS) to revised beliefs after psychedelics (REBAS)

The Relaxed Beliefs Under pSychedelics (REBUS) model proposes that serotonergic psychedelics decrease the precision weighting of neurobiologically-encoded beliefs. We conducted a preliminary examination of two psychological assumptions of REBUS: (a) psychedelics foster acute relaxation and post-acute revision of confidence in mental-health-relevant beliefs; which (b) facilitate positive therapeutic outcomes and are associated with the entropy of EEG signals. Healthy individuals (N = 11) were administered 1 mg and 25 mg psilocybin 4-weeks apart. Confidence ratings for personally held beliefs were obtained before, during, and 4-weeks post-psilocybin. Acute entropy and subjective experiences were measured, as was well-being (before and 4-weeks post-psilocybin). Confidence in negative self-beliefs decreased following 25 mg psilocybin. Entropy and subjective effects under 25 mg psilocybin correlated with decreases in negative self-belief confidence (acutely and at 4-weeks). Particularly strong evidence was seen for a relationship between decreases in negative self-belief confidence and increases in well-being. We report the first empirical evidence that the relaxation and revision of negative self-belief confidence mediates psilocybin's positive psychological outcomes, and provide tentative evidence for a neuronal mechanism, namely, increased neuronal entropy. Replication within larger and clinical samples is necessary. We also introduce a new measure for examining the robustness of these preliminary findings and the utility of the REBUS model.

Cannabis combined with oxycodone for pain relief in fibromyalgia pain: a randomized clinical self-titration trial with focus on adverse events

Objectives

We determined whether adding cannabis to oxycodone for chronic non-cancer pain management could reduce treatment-related adverse effects (AEs) while maintaining effective analgesia.

Methods

In this open-label study, fibromyalgia patients aged ≥18 years were randomized to receive 5 mg oxycodone tablets (max. four times/day), 150 mg of inhaled cannabis containing 6.3% Δ9-tetrahydrocannabinol and 8% cannabidiol (max. times inhalation sessions/day), or a combination of both for 6 weeks. The primary endpoint was treatment-related adverse events, assessed using a 10-point composite adverse event (cAE) score; additionally, we recorded daily reported pain relief and daily tablet and cannabis consumption.

Results

In total, 23 patients were treated with oxycodone, 29 with cannabis, and 29 with the oxycodone/cannabis combination. Three patients from the oxycodone group (13%) and 18 patients from the cannabis groups (31%, 9 in each group) withdrew from the trial within 2-3 weeks because of the severity of AEs. There were no differences in treatment-related cAE scores among the three groups that completed the study (p = 0.70). The analgesic responder rate showed a ≥1- point reduction in pain in 50% and a ≥2-point reduction in 20% of patients, while 50% of patients experienced no treatment benefit. The combination treatment reduced oxycodone tablet consumption by 35% (p = 0.02), but it did not affect the number of cannabis inhalation sessions.

Conclusions

Cannabis combined with oxycodone offered no advantage over either treatment alone, except for a reduction in opioid tablet intake; however, the overall drug load was the highest in the combination group. Moreover, cannabis was poorly tolerated and led to treatment discontinuation in one-third of participants treated with cannabis.

Clinical Trial Registration

The trial was registered at the WHO International Clinical Trials Registry Platform (trialsearch.who.int) on July 26, 2019, identifier NL7902.

Masking Influences: A Systematic Review of Placebo Control and Masking in Psychedelic Studies

Psychedelic-assisted therapy is becoming increasingly acknowledged as an effective therapeutic intervention for various psychiatric illnesses. However, the evaluation of masking success is rarely reported in trials. The objective of the present systematic review was to evaluate placebo-control and masking in studies exploring psychedelic-assisted therapy. Nine (k = 9) studies dating between January 2010 and March 2023 were retrieved using six databases, following strict inclusion and exclusion criteria. The results show that almost 78% of the studies had, at best, "poor" masking success. At the same time, 60% of active placebo and 75% of inactive placebo studies showed large effect sizes. In other words, masking influences, including benign unmasking, cannot be excluded. We therefore conclude that efficacy of psilocybin, Ayahuasca, or LSD is only one of the possible interpretations of large, positive changes in symptomatology for patients suffering from, for example, alcohol use disorder, anxiety with or without life-threatening disease, anxiety and/or depression with life-threatening cancer, treatment-resistant depression or major depressive disorder. We recommend care be taken to increase successful masking procedures and discuss alternative treatment designs to better control for potential masking influences.

Psychological flexibility as a mechanism of change in psilocybin-assisted therapy for major depression: results from an exploratory placebo-controlled trial

Several phase II studies have demonstrated that psilocybin-assisted therapy shows therapeutic potential across a spectrum of neuropsychiatric conditions, including major depressive disorder (MDD). However, the mechanisms underlying its often persisting beneficial effects remain unclear. Observational research suggests that improvements in psychological flexibility may mediate therapeutic effects. However, no psychedelic trials to date have substantiated this finding in a clinical sample. In an exploratory placebo-controlled, within-subject, fixed-order study, individuals with moderate to severe MDD were administered placebo (n = 19) followed by psilocybin (0.3 mg/kg) (n = 15) 4 weeks later. Dosing sessions were embedded within a manualized psychotherapy that incorporated principles of Acceptance and Commitment Therapy. Depression severity, psychological flexibility, mindfulness, and values-congruent living were measured over a 16-weeks study period. Psychological flexibility, several facets of mindfulness, and values-congruent living significantly improved following psilocybin and were maintained through week 16. Additionally, improvements in psychological flexibility and experiential acceptance were strongly associated with reductions in depression severity following psilocybin. These findings support the theoretical premise of integrating psilocybin treatment with psychotherapeutic platforms that target psychological flexibility and add to emerging evidence that increasing psychological flexibility may be an important putative mechanism of change in psilocybin-assisted therapy for MDD and potentially, other mental health conditions.