My SWAG would be the numbers of people for whom the side effects of Topamax are intolerable. I learned from my experiences with IBD that very often any particular medication/treatment only works for a portion of patients, and since there's no way to tell in advance, we're stuck with being guinea pigs to find out which one(s) will work (best) for each of us.

For some gabapentin works fine. For others like you, gabapentin is horrible, but Lyrica or Topamax may work. For some, like me, none of them work, or the side effects of each/all are intolerable.

It'd be nice if one medication worked well for eveyone without intolerable side effects, but it'd be even nicer if we all had our health, no pain, and were all rich...

Doc