It has previously been shown that nitroglycerine induces cluster headache attacks in episodic cluster headache patients (ECH patients) in bouts but not in remission phase. Furthermore, plasma concentrations of calcitonin gene-related peptide (CGRP) have been shown to be significantly higher during, but not before and after, an attack.

The attack appears around 20-40 min after nitroglycerine infusion with vasodilatation. During this latency period preceding the attack, no increase in CGRP plasma concentrations is seen. CGRP induces migraine attacks in 65% of migraine patients, and CGRP antagonists as well as monoclonal antibodies against CGRP are effective in migraine treatment.

Based on the above the investigators hypothesize the following:

1. Provoking ECH patients in bout with CGRP triggers cluster headache attacks
2. Provoking ECH patients in remission with CGRP does not trigger cluster headache attacks
3. Provoking chronic cluster headache patients with CGRP triggers cluster headache attacks more often than in ECH patients.

Inclusion Criteria:

• Fulfillment of IHS criteria for cluster headache either chronic or episodic
• Patients in bouts 1-32 attacks per week
• Patients in remission minimum of 1 month remission time
• fertile women must use safe contraception

Exclusion Criteria:

• All other primary types of headache
• headache 8 hours or less before study day begins
• pregnant or lactating women
• any history or clinical sigs of hyper/hypotension, heart disease, mental disorder, substance abuse, or other illness deemed relevant by the medical doctor assessing the patient