A phase 2b randomized clinical trial tested 25 mg of psilocybin with psychotherapy against a 5 mg dose and a placebo (nicotinamide) in 144 adults aged 25 to 65 with treatment-resistant depression who had stopped antidepressants. The primary outcome—a 50% or greater reduction in depression scores at six weeks—was not statistically significant: 17.0% of those receiving 25 mg responded, versus 12.5% on 5 mg and 10.6% on placebo. Exploratory analyses suggested a clinically meaningful reduction in depressive symptoms with the 25 mg dose. The treatment was generally well tolerated, but safety signals included higher reports of suicidal ideation on dosing days and two serious adverse reactions, one case of hallucinogen persisting perception disorder.
Psilocybin treatment works differently from standard psychiatric medication, potentially offering rapid and lasting benefits across multiple diagnoses. It may improve not just symptoms but broader aspects of mental health, suggesting it could modify the underlying disease process and promote well-being. Psychedelic-assisted psychotherapy might become the first disease-modifying treatment in psychiatry.
A single 25 mg dose of psilocybin, or two such doses given six weeks apart, combined with psychotherapy produced a stable and clinically meaningful reduction in depression symptoms for up to twelve months in people with treatment-resistant depression. The average improvement on the Hamilton Rating Scale for Depression was about 7.9 points at six months and 7.7 points at twelve months, with no significant difference between dosing groups. Restarting standard antidepressant medication during follow-up was strongly linked to higher depression scores. This naturalistic follow-up of a phase 2b trial is the largest and most complete long-term assessment of psilocybin for depression to date.