04 Nov 2022 --- Mental health company Compass Pathways has led a landmark study across 22 international sites and 10 countries to understand the effects of psilocybin on depression. They found that a 25 mg dose of psilocybin combined with psychological support reduced depression symptoms significantly for participants with treatment-resistant depression – the condition of not responding to at least two antidepressants.Psilocybin is a naturally occurring psychedelic prodrug compound produced by more than 200 species of fungi.