The purpose of this study is to evaluate whether RWJ-333369 is a safe and effective treatment in reducing the number of migraine headaches when added to a person's usual medications for acute migraine headache relief.

Inclusion Criteria:

• Established history of migraines for at least 1 year;
• Have between 3 and 12 migraine attacks per month, and no more than 15 headache days in total per month;
• Migraines must have first started before age 50.

Exclusion Criteria:

• Most frequent headache type is not migraine;
• Failed 3 or more studies of effective migraine-preventing medications;
• Overuse of pain medications to treat migraines;
• Not willing to stop use of migraine-preventing medications;
• Significant serious concomitant diseases.