Meta-analysis highlights potential of psilocybin therapy for treatment-resistant depression

A scientific review and meta-analysis published in Psychiatry Research concludes that “well-designed phase III trials are urgently needed” to further examine the promising effects of psilocybin-assisted psychotherapy in patients with major depression and life-threatening cancer. These pivotal trials would assess the safety and efficacy of this novel approach in comparison to existing standard treatments, potentially establishing psilocybin-assisted psychotherapy as an accepted medical alternative.

The new research was spurred by a pressing need to find effective treatments for depression, particularly for those forms of the condition that do not respond to traditional treatments. Despite advancements in mental health therapies, many patients with major depressive disorder or severe depression related to life-threatening cancer find little relief even after trying multiple treatments. This scenario, known as treatment-resistant depression, affects over 30% of patients treated for major depressive disorder, highlighting the urgency for alternative therapeutic approaches.

Psilocybin, a naturally occurring psychedelic compound found in certain types of mushrooms, has long intrigued researchers due to its potential therapeutic effects. In psilocybin-assisted psychotherapy, patients are given controlled doses of psilocybin in a clinical setting, accompanied by professional psychological support. This innovative approach aims to create a setting in which patients can explore their thoughts and emotions under the influence of psilocybin, which is known to induce a heightened state of openness and introspection. The therapy sessions typically include a preparation phase, the psilocybin administration session, and subsequent integration sessions, where patients process their experiences.

“There has been a lot of buzz in both the media and academic circles about psilocybin’s efficacy in major depressive disorder,” explained study authors Sipan Haikazian, David Chen-Li, and Joshua Rosenblat of Toronto Western Hospital. “Numerous trials have been published in recent years demonstrating psilocybin’s profound antidepressant effects in randomized, placebo-controlled clinical trials, the gold standard for determining the efficacy of a drug.”

“The Mood Disorders Psychopharmacology Unit (MDPU) at Toronto Western Hospital is conducting trials for psychedelic and psychedelic-like substances for the treatment of mood disorders, so we are familiar with the current state of the field. As such, we believed a formal review of the evidence was warranted and conducted both a quantitative and qualitative analysis to summarize the state of the field at this time.”

Free daily newsletter

A meta-analysis, a statistical technique used to combine results from multiple studies to arrive at a comprehensive conclusion, was employed in this research. This approach is particularly useful in health sciences as it provides a more robust and reliable overview than individual studies. The researchers meticulously searched through various scientific databases to find studies that examined the antidepressant efficacy of psilocybin combined with psychotherapy.

They sifted through thousands of publications, eventually focusing on 13 randomized controlled trials that met their strict criteria. The studies had to include participants with a confirmed diagnosis of major depressive disorder or distressing depressive symptoms associated with life-threatening cancer. This diagnosis needed to be based on standard clinical assessments or structured interviews, such as those outlined in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). The combined sample included 686 individuals.

The analysis showed that patients receiving psilocybin therapy exhibited significantly more improvement in depressive symptoms than those who did not receive this treatment. This improvement was consistent across various subgroups, including patients with major depressive disorder and those experiencing depression due to life-threatening cancer.

Notably, the study found that both response rates (the proportion of patients showing a significant reduction in depression symptoms) and remission rates (the proportion of patients whose symptoms subsided to the point of being considered in remission) were higher in the psilocybin group compared to controls.

Furthermore, the effects of psilocybin were observed shortly after administration, suggesting a rapid onset of antidepressant action. This is a significant departure from traditional antidepressants, which typically require a longer period to start working. Interestingly, the study also found that the positive effects of psilocybin therapy could last for several months, an encouraging sign for its long-term efficacy.

The study found that while psilocybin was generally well-tolerated, some participants did experience non-serious side effects. Commonly reported adverse events included headaches, nausea, fatigue, and transient anxiety. These are typical of psychedelic-assisted therapies and are usually manageable within the controlled setting of the therapy sessions. Importantly, serious adverse events were rare.

However, there were isolated instances of more concerning effects, such as worsening depressive symptoms or suicidal ideation, particularly in individuals with a history of such issues. This highlights the need for careful screening and monitoring of participants in psilocybin therapy, especially those with a complex psychiatric history.

A significant limitation is the lack of active comparators, which could lead to expectancy bias. Including active comparators that mimic the psychoactive effects of psilocybin would strengthen the reliability of the results, as it would more effectively control for the influence of participants’ expectations on their reported outcomes.

“The average person should approach the findings of our paper with cautioned optimism, particularly with how psilocybin should be used in both clinical and non-clinical settings,” Haikazian, Chen-Li, and Rosenblat told PsyPost. “While the effect size (a measure of how effective psilocybin is at reducing depressive symptoms compared to placebo) of psilocybin was moderate, the studies have several limitations. It is difficult to find a placebo drug that can mimic psilocybin’s obvious psychological effects while not having the depressive action. In fact, such a drug does not yet exist.”

“Therefore, it’s very possible that participants in studies were unblinded in regards to what treatment they received,” the researchers explained. “Also, despite positive findings, psilocybin should only be prescribed in a monitored, clinical setting, and we nor any of the authors of these studies condone or promote self-medication with the drug. This is particularly important to highlight given the increasing presence of illicitly yet conspicuously sold psilocybin in large urban centres.”

The study, “Psilocybin-Assisted Therapy for Depression: A Systematic Review and Meta-Analysis“, was authored by Sipan Haikazian, David C.J. Chen-Li, Danica E. Johnson, Farhan Fancy, Anastasia Levinta, M. Ishrat Husain, Rodrigo B. Mansur, Roger S. McIntyre, and Joshua D. Rosenblat.