• Change in migraine days, migraine periods, and migraine attacks compared between the topiramate group and placebo group at the last month of the baseline phase and the last month of the placebo-controlled phase
  

• Health-related quality of life as recorded in patient questionnaires (MIDAS, HIT-6, MSQ) over 16 double-blind weeks; Patient's satisfaction with the effectiveness and safety of topiramate; Safety
  

Previous studies have shown that topiramate is effective in preventing chronic migraine headaches. This study will start with a 4-week baseline period in which no treatment is given, followed by a 12-week period in which each patient's dose is adjusted and then kept stable for the last 4 weeks of the 16-week double-blind phase. The individualized dose will start at 25 milligrams of topiramate per day and will be increased 25 milligrams per day once weekly and then raised to either the target--100 milligrams per day--or the maximum dose that is well tolerated up to 200 milligrams per day. Patients who are randomized to receive topiramate will remain on the optimized dose. The comparison phase of the study is a 16-week period in which the change in migraine days of patients on topiramate (taking at least 50 milligrams per day) is compared with the change in migraine days for patients on the placebo. Also studied will be the patients' health-related quality of life as assessed by questionnaires filled out at specific visits as well as the patients' views of the safety and tolerability of topiramate. The study hypothesis is that the number of migraine days, periods, and attacks from the baseline period to the last 4 weeks in the double-blind period is reduced more in the topiramate group than the placebo group. During the 16-week comparison period, patients will take by mouth a dose of 50 milligrams to 200 milligrams of topiramate daily.