Depression affects more than 300 million people globally. Unfortunately, current treatment options are limited in their effectiveness and have side effects that reduce treatment adherence. Emerging research suggests psilocybin may be a safe and effective treatment for depression, with long-lasting results after one to two sessions.

Psilocybin is the psychoactive compound found in hallucinogenic mushrooms of the Psilocybe genus and others. Recent research has greatly expanded the understanding of psychedelic drugs and their effects on mental illness. For example, ketamine, a short-acting anesthetic with hallucinogenic effects, is available for use in the United States to treat depression, anxiety, and post-traumatic stress disorder. Psilocybin may provide similar benefits with a lower risk of chemical addiction, however.

Adults with depression who were not taking antidepressant medication were invited to participate in either immediate psilocybin treatment or be placed on an eight-week waitlist for treatment. Twenty-four participants completed the study treatment of two psilocybin sessions with supportive psychotherapy. The authors used a standardized rating scale called the GRID-Hamilton Depression Rating Scale (GRID-HAMD) to measure depression severity.

One week after psilocybin treatment, participants reported a statistically significant decrease in depression symptoms (average GRID-HAMD score = 8.0, mild depression) compared to those on the waitlist (average GRID-HAMD score = 23.8, very severe depression). This effect remained four weeks post-treatment with participants in the immediate treatment group reporting average GRID-HAMD scores of 8.5 compared to 23.5 in the waitlist group. Nearly three-fourths of all participants experienced a 50 percent or greater reduction in depression symptoms by four weeks following psilocybin treatment.

Previous research by these investigators has reported similar results in patients with cancer and depression. The authors suggested these findings demonstrate the ability of psilocybin-assisted therapy to produce large, rapid, and sustained improvement in people who have depression.

• Link to full study.

• Psilocybin expert Dr. Roland Griffiths is the corresponding author for this study. Watch this clip in which he discusses psilocybin use and mental illness.