To develop a pragmatic migraine model the investigators will induce headache in patients with migraine without aura with a phosphodiesterase inhibitor (cilostazol). If the headache responds to sumatriptan injection, the model can be used to test new drug candidates.

There remains a great need for more effective anti-migraine drugs with fewer side effects. Human experimental models are valuable in early phase development of new anti-migraine drugs but useful models have not yet been developed. The investigators' group has shown that Cilostazol, a phosphodiesterase inhibitor induce headache/migraine in both healthy volunteers and in patients with migraine without aura (MO). To validate this model, the headache must respond to specific migraine treatment with sumatriptan.

Hypothesis: Cilostazol induces a migraine-like headache in MO-patients and the induced headache responds to sumatriptan injection Aim: Developing a pragmatic and valid model for the testing of new anti-migraine drugs.

Inclusion Criteria:

• Migraine patients who meet IHS criteria for migraine with or without aura of both sexes
• 18-70 years
• 45-95 kg.

Exclusion Criteria:

• Any other type of headache then migraine without aura (except episodic tension-type headache < 1 day per week)
• Serious somatic or psychiatric disease
• Pregnancy
• Intake of daily medication (except oral contraceptives)
• Triptan non-responders