A 2006 randomized controlled trial^[8] provided 9 participants with 25, 100, 200, or 300 μg of psilocybin. The participants experienced varying degrees of symptom improvement within 1 day of treatment.
A 2011 randomized controlled trial^[9] provided 0.2 grams of psilocybin per kilogram of body weight (0.2 mg/kg) to 12 participants with advanced-stage cancer and cancer-related anxiety. After 6 months, the participants experienced significant mood improvements from baseline.
A 2014 open-label study^[10] provided moderate (20 mg/70 kg of body weight) and high (30 mg/70 kg) doses of psilocybin to 15 nicotine-dependent smokers as part of a 15-week smoking cessation protocol. Twelve of the 15 participants demonstrated abstinence at a 6-month follow-up.
A 2015 proof-of-concept study^[11] provided psilocybin (0.3 mg/kg at session 1 and 0.4 mg/kg at session 2 four weeks later) to 10 participants with DSM-IV alcohol dependence. There was a reduction in drinking days and heavy drinking days at 28 weeks after the second psilocybin dose.
A 2016 open-label study^[12] provided two doses of psilocybin (10 mg and 25 mg), separated by 7 days, to 12 participants with moderate-to-severe, unipolar, treatment-resistant depression. The participants experienced reductions in depression symptoms at 1 week and 3 months after the 25 mg treatment.
A 2016 randomized controlled trial^[13] provided a single dose of 0.3 mg/kg of psilocybin or placebo, in conjunction with psychotherapy, to 29 participants with life-threatening cancer and clinically significant anxiety/depression. Psilocybin reduced anxiety and depression symptoms acutely and at a 33-week follow-up.
Another 2016 randomized controlled trial^[14] provided a very low, placebo-like dose (1–3 mg/70 kg of bodyweight) and a high dose (22 or 30 mg/kg), with 5 weeks between sessions, to 51 participants with life-threatening cancer and symptoms of depression or anxiety. High-dose psilocybin produced immediate decreases in symptoms of depression and anxiety; these improvements were largely sustained at the 6-month follow-up.
A 2020 meta-analysis^[15] of 4 studies reported that participants had significant reductions in anxiety and depression symptoms posttreatment and at the 6-month follow-up.
A subsequent 2020 meta-analysis^[16] of 92 participants across 3 studies reported that the participants taking psilocybin in doses of 0.2–0.4 mg/kg experienced reduced scores on depression and anxiety scales compared to a control group, with no adverse effects reported. There were short-term, transient increases in blood pressure and heart rate, which returned to normal 6+ hours after psilocybin administration.
A 2021 randomized controlled trial,^[17] previously reviewed in Study Summaries, compared the efficacy of psilocybin compared to escitalopram in 59 participants with moderate-to-severe depression. Participants in both groups experienced improvements in depression scores at 6 weeks after treatment.

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