The investigators wish to investigate neurobiological effects of serotonin 2A receptor modulation in healthy volunteers, contrasting effects of an agonist (psilocybin) and an antagonist (ketanserin). Magnetic resonance imaging (MRI) and positron emission tomography (PET) will be used as neuroimaging tools.

This project applies an experimental medicine strategy coupled with human functional and molecular neuroimaging to elucidate the effects of 5-HT2A receptor (5-HT2AR) modulation on brain function and mood in healthy individuals. We compare psilocybin (5-HT2AR agonist) and ketanserin (5-HT2AR antagonist) effects on brain function to identify neural mechanisms mediating the clinical effects of psilocybin and, more broadly, to establish this comparative strategy as a pathway for delineating pharmacological effects on the brain in humans.

Inclusion Criteria:

1) Healthy individuals above 18 years of age.

Exclusion Criteria (For Subprojects 1, 2a, 2b, and 3):

1. Presence of or previous primary psychiatric disease (DSM axis 1 or WHO ICD-10 diagnostic classifications) or in first-degree relatives.
2. Previous or present neurological condition/disease, significant somatic condition/disease or intake of drugs suspected to influence test results.
3. Non-fluent Danish language skills.
4. Vision or hearing impairment.
5. Previous or present learning disability.
6. Pregnancy.
7. Breastfeeding.
8. Contraindications in regard to MRI scanning.
9. Alcohol or drug abuse.
10. Allergy to test drugs.
11. Participation in studies in which participant has received more than 10 mSv of radiation or other significant exposure to radiation.
12. Abnormal ECG or intake of QT prolonging medication.
13. Previous significant side-effects in regard to hallucinogenic drugs.
14. Use of hallucinogenic drugs 6 months previous to inclusion.
15. Blood donation 3 months before and after project participation
16. Body weight under 50 kg.
17. Plasma ferritin levels outside normal range

Exclusion Criteria (For Subproject 2c):

1. Presence of or previous primary psychiatric disease (DSM IV axis 1 or WHO ICD-10 diagnostic classifications).
2. Presence of or previous primary psychiatric disease with psychosis symptoms or hypomania (DSM IV axis 1 [drug/alcohol abuse/dependence, schizophrenia and other psychoses] or WHO ICD-10 diagnostic classifications [F10-29, as well as F30-39 with psychotic symptoms, F60]) in first-degree relatives (parents or siblings).
3. Previous or present neurological condition/disease, significant somatic condition/disease or intake of drugs suspected to influence test results.
4. Non-fluent Danish language skills or pronounced vision or hearing impairment.
5. Previous or present learning disability.
6. Pregnancy.
7. Breastfeeding.
8. Contraindications in regard to MRI scanning.
9. Alcohol or drug abuse.
10. Allergy to test drugs.
11. Abnormal ECG or intake of QT prolonging medication.
12. Previous significant side-effects in regard to hallucinogenic drugs.
13. Previous use of hallucinogenic drugs.
14. Body weight under 45 kg.
15. Ethical concerns regarding the administration of a psychedelic drug.

Via database of Center for Integrated Molecular Brain Imaging (Knudsen et al 2016, NeuroImage) data will be available for neuroscience research community contingent on approval by scientific board.

Upon project completion

All researchers can request access to data from the database by completing a standardized application form to provide detailed information about the specific database request. The application form and guidelines are available here. Please note that there are some formal requirements that must be fulfilled if the data request is from an international researcher. For example we do not have permission for sharing data outside of the EU, so researchers from a non-EU country will have to come here to work on the data instead.