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)