available over the counter: no

uses: to prevent vascular headaches such as migraines and cluster headaches;  because of risk of side effects, used only as a last resort;  not useful against headaches which have already begun

mechanism of action: not known;  probably causes constriction of blood vessels

side effects
• common: diarrhea, dizziness, light headedness, drowsiness, nausea, vomiting
• less common: vision changes, changes in heartrate, loss of appetite
• serious: shortness of breath, wheezing, chest pain, changes in urine output, swelling of body

concerns: discontinue use of drug gradually over 2 to 3 weeks; for prolonged use, after every 4 month course, discontinue the drug for 4 weeks before starting the next course;  do not drive or operate heavy machinery