Effects of LSD on Neuroplasticity in Healthy Subjects

Inclusion Criteria: 1. Aged 21-55 2. Body mass index 18-29 3. Right-handed as assessed by the Edinburgh Handedness Inventory (score \> 60) 4. Fluent understanding of German 5. Willingness to adhere to study protocol 6. Willingness to refrain from taking illicit psychoactive substances for the duration of the study 7. Willingness to refrain from consuming alcohol for 24 hours before each study appointment. 8. Willingness to not operate a motor vehicle or other heavy machinery 48 hours after each substance administration. 9. Women of childbearing potential must be willing to use effective birth control during the study (e.g. birth control pill; condoms must be combined with a second reliable method). 10. Women of childbearing potential must have a negative pregnancy test at the beginning of the study. Pregnancy tests will be repeated before each treatment day and must remain negative. 11. A friend or relative must be available to accompany the participant home following LSD appointments. Exclusion Criteria: 1. Severe chronic or acute medical condition 2. History of any seizure disorder, stroke, or cardiovascular illness 3. History of severe head trauma resulting in loss of consciousness 4. Personal or family history (first-degree relative) of psychotic disorders 5. Current or previous major neurological or psychiatric disorder within the last 3 years (e.g. major depression, anorexia, substance use disorder), 6. History of medically relevant suicide attempts 7. Current use of psychoactive medications 8. Lifetime use of hallucinogens, dissociatives, or entheogens more than 10 times, or any time within the previous three months 9. Regular (daily or near-daily) use of cannabis, alcohol, nicotine, or illicit substances 10. Pregnant or nursing women 11. Presence of any implanted, metal or electronic devices (e.g. pacemaker) 12. Recent or current participation in another clinical trial