A Swedish randomised trial found that one 25 mg dose of psilocybin reduced depression within days, but its clinician-rated advantage over niacin placebo was no longer significant after a year.

The trial involved 35 adults with moderate-to-severe recurrent major depressive disorder, all of whom received five psychotherapeutic support sessions. Psilocybin improved clinician-rated symptoms more than 100 mg niacin by day 8, with benefits persisting through day 42 but not differing significantly from placebo at day 365.