LSD Occupancy of the Serotonin 2A Receptor in the Human Brain

Inclusion Criteria: • Healthy individual between 18-75 years old Exclusion Criteria: * Current or past history of primary psychiatric illness (The Diagnostic and Statistical Manual of Mental Disorders IV axis-I or World Health Organisation International Classification of Diseases-10 diagnostic classification) * Current or past history of primary psychiatric illness (The Diagnostic and Statistical Manual of Mental Disorders IV axis-I or World Health Organisation International Classification of Diseases-10 diagnostic classification) in a first degree relative (i.e., parents, siblings) * Current or past history of neurological disease, significant somatic condition/disease * Use of medication that could potentially influence results (e.g.., drugs that act on relevant components of the serotonin system or may interfere with metabolism of study drug) * Non-fluent Danish language skills * Profound visual or auditory impairments * Severe learning disability * Pregnancy on the scan date, verified by a pregnancy test (test omitted if confirmed that individual is post-menopausal) * Lactation (females) * Contraindications for magnetic resonance imaging (e.g., pacemaker, claustrophobia, etc.) * Contraindications for positron emission tomography * Alcohol or drug abuse * Allergy to administered compounds * Participant in research study with \>10 millisievert exposure within the past year or significant occupational exposure to radioactive substances * Abnormal ECG (ECG indicating current or previous heart disease or predisposition to heart disease, e.g., QT prolongation) or use of QT prolonging medication * Use of psychedelic substance within the preceding six months * Blood donation up to three months before the study (i.e., more than 500ml of blood) * Head injury or concussion resulting in loss of consciousness for more than 2 min * Haemoglobin levels \< 7.8 mmol/l for women and 8.4 mmol/l for men * Ferritin levels outside normal range (12-300 µg/L) * Body-weight \< 50 kg or \> 110kg * body-mass index \> 35 * Individual assessment by research staff deeming drug administration unsafe due to ethical or psychological circumstance of the participant