The Effectiveness and Safety of Topiramate on Prevention of Chronic Migraine

Inclusion Criteria: * History of migraine for \>= 1 year * Headache type meets HIS (International Headache Society) criteria for migraine * History reflects "chronic" headache--an average of \>= 15 migraine days per month in the 3 months preceding trial entry * History of chronic migraine for \>=1 year\>=15 headaches per month with an average duration of 4 hours if not treated * Patient is otherwise neurologically and physically healthy on a pre-trial exam. Exclusion Criteria: * Any other type of chronic headache (besides migraine) from section 2 to 13 of the International Headache Society classification or headache resulting directly resulting some other factor (except for medication overuse) * Onset of migraine after age 50 * Use of an anticonvulsant drug in the month prior to trial entry * Use of an antidepressant unless dose has been used at a stable dose for \>=3 months * Use of migraine prevention medicine in the 3 months prior to trial entry unless the drug has been used for at least 3 months and used at a stable dose for at least a month * Use of a carbonic anhydrase inhibitor such as acetazolamide (used to treat high blood pressure, glaucoma and seizures) or triamterene (a "water pill" for swelling and high blood pressure).