The Impact of Dose on the Impairing, Intoxicating, and Abuse-Related Effects of Psilocybin

Inclusion Criteria:

* Be at least 21 years old,
* Be in good general health based on screening procedures (e.g., physical exam, blood testing, psychiatric evaluation),
* Have vital signs in normal range,
* Have not donated blood in past 30 days,
* Not be pregnant (assessed via blood serum at screening and urinalysis before each study session) or breast feeding (women only),
* Have a body mass index (BMI) in the range of 18 to 36 kg/m2,
* Report using psilocybin at least once in the participant's lifetime, but not in the past month,
* Negative urine test for illicit drug use (not including cannabis) and negative breath alcohol test (0% breath alcohol concentration) at screening and before study sessions.

Exclusion Criteria:

* Psychoactive drug use (aside from nicotine, alcohol, caffeine, cannabis) in past month,
* Current use of over the counter (OTC) drugs, supplements/vitamins, or prescription medications that, in the opinion of the investigator or medical staff, will impact the participant's safety,
* History of or current evidence of significant medical condition that would impact participant's safety (e.g., hypertension, epilepsy),
* Evidence of current psychiatric condition (based on MINI),
* Family history of 1st degree relative with psychotic disorder or bipolar 1 disorder,
* Clinical institute withdrawal assessment for alcohol-revised (CIWA-Ar) score \>9 (which indicates that severe withdrawal),50
* Enrollment in another clinical trial or receiving of any drug as part of research within past 30 days, and
* Shipley vocabulary score \<18 (corresponds to 5th grade reading level).