A single supervised dose of psilocybin, the psychoactive compound in so-called magic mushrooms, produced large and lasting reductions in depression symptoms among patients who had failed multiple prior treatments, according to results from the first randomized, placebo-controlled trial of the therapy run inside Britain's public health system.
The trial, known as PsiDeR and published in Nature Medicine, enrolled 60 adults with treatment-resistant major depressive disorder at a single National Health Service site in England, led by researchers at King's College London and South London and Maudsley NHS Foundation Trust. Every participant had already failed at least two antidepressant medications, or one medication plus a course of psychotherapy — the clinical definition of treatment resistance used in the study.
Study design and results
Participants were randomly assigned, under double-blind conditions, to receive either a 25-milligram oral dose of synthetic psilocybin or an inactive placebo, each paired with structured psychological support: preparatory sessions beforehand, a monitored six-hour dosing session, and integration therapy afterward. By six weeks, 50 percent of those who received psilocybin met the criteria for treatment response and 40 percent were in full remission, compared with 3 percent of the placebo group on both measures — a gap researchers described as large by the standards of depression trials. The psilocybin group also reported more non-serious side effects than the placebo group, mostly mild and transient, while serious adverse events were rare and not attributed to the drug in either arm.
Publicly funded clinical trials are an important part of the jigsaw of evidence.
Professor James Rucker, King's College London, lead investigator
What the trial can't yet tell us
The study's authors were explicit about its limits. With only 60 participants at a single site, it was designed primarily as a feasibility trial — testing whether a rigorous, placebo-controlled design could even be run within routine NHS care — rather than a definitive efficacy study. Psilocybin's perceptual effects also made it difficult to keep participants and therapists fully blind to who had received the active drug, a problem known as functional unblinding that can inflate apparent benefits if patients' and clinicians' expectations shift accordingly. The sample also had limited ethnic diversity, and the researchers noted that expectancy effects likely account for some portion of the observed difference between groups.
The results broadly echo earlier, industry-funded psilocybin trials for treatment-resistant depression, lending some independent support to those findings, but researchers caution that larger, multi-site confirmatory trials are still needed before the therapy could be considered for wider use. Psilocybin remains a controlled substance in the United Kingdom outside of licensed research settings, and any future rollout would require both regulatory approval and a workforce trained to deliver the intensive, multi-session therapy safely.
Still, the trial's organizers frame it as an important proof of concept: that a treatment developed largely through privately funded research can be tested, and potentially delivered, through a public health system rather than only in specialty clinics able to charge for it.
