Effects of SERT Inhibition on the Subjective Response to Psilocybin in Healthy Subjects

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 24 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. Exclusion Criteria: 1. Chronic or acute medical condition, including a history of seizures. 2. Current or previous major psychiatric disorder (e.g. psychotic disorders, mania / hypomania, anxiety disorders, and substance abuse). 3. Psychotic disorder in first-degree relatives, not including psychotic disorders secondary to an apparent medical reason, e.g. brain injury, dementia, or lesions of the brain. 4. Illicit substance use (with the exception of cannabis) more than 10 times or any time within the previous two months. 5. History of an angle closure glaucoma. 6. Pregnant or nursing women. 7. Participation in another clinical trial (currently or within the last 30 days). 8. Use of medications that may interfere with the effects of the study medications (any psychiatric medications and any medication with known pharmacokinetic or pharmacodynamic interactions with escitalopram). 9. A corrected QT time (QTc), calculated by Bazett's formula, of over 450 milliseconds in males and over 470 milliseconds in females. 10. Tobacco smoking (\>10 cigarettes/day). 11. Consumption of alcoholic drinks (\>10 drinks / week). 12. Bodyweight \< 45 kg.