Methysergide is an oral, synthetic ergot alkaloid, structurally related to the oxytocic agent methylergonovine and to the potent hallucinogen LSD. Methysergide is used prophylactically to reduce the frequency and intensity of severe vascular headaches. Although methysergide is an ergot alkaloid, it is a weak vasoconstrictor and oxytocic. Methysergide is a more potent antagonist of peripheral serotonin receptors than other ergot alkaloids. Methysergide is not just a 5HT2 antagonist, it is also a 5HT1 agonist. Although methysergide and sumatriptan both stimulate serotonin receptors centrally, methysergide is intended for prophylaxis while sumatriptan is indicated for treatment of an acute attack. Methysergide was approved by the FDA in 1962. Methysergide was formerly used for prophylaxis of cluster headaches/migraine headaches, but is no longer recommended due to retroperitoneal/retropulmonary fibrosis.