Inclusion Criteria:  Understanding of the German language. Understanding the procedures and the risks that are associated with the study. Participants must be willing to adhere to the protocol and sign the consent form. Participants must be willing to refrain from taking illicit psychoactive substances during the study. Participants must be willing to abstain from xanthine-based liquids from the evenings prior to the study sessions and during the sessions. Participants must be willing not to drive a traffic vehicle or to operate machines within 48h after substance administration. Willing to use double-barrier birth control throughout study participation. Body mass index between 18-29 kg/m2.  Exclusion Criteria:  Chronic or acute medical condition, including a history of seizures. Current or previous major psychiatric disorder (e.g. psychotic disorders, mania / hypomania, anxiety disorders). 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. Hypertension (SBP>140/90 mmHg) or hypotension (SBP<85 mmHg); QT-time>450 ms (men) or >470 ms (women). Use of hallucinogenic substances (not including cannabis) more than 20 times or any time within the previous two months. History of acute glaucoma. Pregnant or nursing women. Participation in another clinical trial (currently or within the last 30 days). 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 paroxetine). Tobacco smoking (>10 cigarettes/day). Consumption of alcoholic drinks (>20 drinks/week).