Topamax works, and by works, I mean reduce migraine frequency and intensity by at least 50% roughly 1 month after being on a treatment dose. And it works in about 60% of patients who try it. This is the best of all prophylactic meds out there (BB, TCA, etc.). Unfortunately, 20% get side effects bad enough to not continue on the med.
It usually starts working at 100 mg daily. Increasing it from 25 mg every week until that dose has often been recommended to prevent major side effects from developing. But, some people get side effects regardless.
Patients who take it for seizures and migraines should be on at least 200-400 mg daily.
Some supplements are worth trying to help with the migranes. magnesium chloride is the best studied one (may help 50% of the time). Other herbs and supplement may be worth trying..as long as they don't break the bank and taken in moderation.
There are plenty of prophylactics out there, so if side effects are a problem, it is worth talking to your doctor about a different med. Of course, never hesitate to bring this up to your doctor.