Direct Comparison of Altered States of Consciousness Induced by LSD and Psilocybin

Inclusion Criteria: 1. Age between 25 and 65 years. 2. Understanding of the German language. 3. Understanding the procedures and the risks that are associated with the study. 4. Participants must be willing to adhere to the protocol and sign the consent form. 5. Participants must be willing to refrain from taking illicit psychoactive substances during the study. 6. Participants must be willing to drink only alcohol-free liquids and no coffee, black or green tea, or energy drink after midnight of the evening before the study session, as well as during the study day. 7. Participants must be willing not to drive a traffic vehicle or to operate machines within 48 h after substance administration. 8. Women of childbearing potential must have a negative pregnancy test at the beginning of the study. Pregnancy tests are repeated before each study session. 9. Women of childbearing potential must be willing to use double-barrier birth control 10. Body mass index 18-29 kg/m2. Exclusion Criteria: 1. Chronic or acute medical condition 2. Current or previous major psychiatric disorder 3. Psychotic disorder in first-degree relatives 4. Illicit substance use (with the exception of cannabis) more than 10 times or any time within the previous two months. 5. Pregnant or nursing women. 6. Participation in another clinical trial (currently or within the last 30 days) 7. Use of medications that may interfere with the effects of the study medications (any psychiatric medications) 8. Tobacco smoking (\>10 cigarettes/day) 9. Consumption of alcoholic drinks (\>10/week) 10. Bodyweight \< 50 kg