As of 2021, research conducted on psilocybin therapy included potential effects on anxiety and depression in people with cancer diagnoses, alcohol use disorder, and treatment-resistant depression

The intensity and duration of the effects of psilocybin are variable, depending on species or cultivar of mushrooms, dosage, individual physiology, and set and setting

Once ingested, psilocybin is rapidly metabolized to psilocin, which then acts on serotonin receptors in the brain. The mind-altering effects of psilocybin typically last from two to six hours, although to individuals under the influence of psilocybin, the effects may seem to last much longer, since the drug can distort the perception of time. Psilocybin has a low toxicity and a low harm potential. In spite of this, possession of psilocybin-containing mushrooms has been outlawed in most countries, and it has been classified as a scheduled drug by many national drug laws.

The effects of psilocybin are highly variable and depend on the mindset and environment in which the user has the experience, factors commonly referred to as set and setting

After ingesting psilocybin, a wide range of subjective effects may be experienced: feelings of disorientation, lethargy, giddiness, euphoria, joy, and depression
Low doses can induce hallucinatory effects. Closed-eye hallucinations may occur, where the affected individual sees multicolored geometric shapes and vivid imaginative sequences. Some individuals report synesthesia, such as tactile sensations when viewing colors. At higher doses, psilocybin can lead to "intensification of affective responses, enhanced ability for introspection, regression to primitive and childlike thinking, and activation of vivid memory traces with pronounced emotional undertones". Open-eye visual hallucinations are common, and may be very detailed although rarely confused with reality