Prophylactic Effects of Psilocybin on Chronic Cluster Headache

Inclusion Criteria: * Age between 18 and 65 * A diagnosis of chronic cluster headache according to IHCD-III. * Ability to separate cluster headache attacks from other types of headache. * A history of at least 4 attacks/week in the last 4 weeks before inclusion Exclusion Criteria: * A history of using a serotonergic hallucinogen for CH. * Participation in any clinical trials within 30 days preceding study enrollment. * Use of other prophylactic CH medication within the last two weeks. * Current use of drugs suspected to interfere with treatment (e.g. antipsychotic medication) or to be hazardous in combination with psilocybin. * Presence of other trigeminal autonomic cephalalgias. * Known hypersensitivity/allergy to multiple drugs (including psilocybin). * A history or presence of any medical and psychiatric condition that might render patient unsuitable for participation. * Present or previous manic or psychotic disorder or critical psychiatric disorder. * Current drug or alcohol abuse. * MRI Contraindications. * Pregnancy or breastfeeding * Not using safe contraception (if fertile woman) * Stroke (\<1 year from inclusion) * Myocardial infarction (\<1 year from inclusion) * Hypertension (\> 140/90 mmHg at inclusion) * Clinically significant arrhythmia (\<1 year from inclusion)