Hi! I have been on Topamax for 3 years as a migraine prevention medication. It was originally intended for epilepsy and now migraine prevention, but pain therapy I've never heard of.
Personally, I have had a great experience with Topamax. There is a generic now that is WAY cheaper than the name brand. The most common side effects are weight loss, tingly hands and feet, and (get this) word finding problems. I've dealt with the word finding problems and weight loss. I'm a pretty average/small build and lost about 20lbs in my first two months on Topamax. Every 6 months I see my neurologist to get weighed and double check my dosage.
I take 50mg in the morning and 100mg at night and plan on taking it for as long as I need. I know other who say it made them feel bad to be on it, but there are other medications I was very sensitive to. Just depends!
I tried Topamax for bipolar psychosis 10 years ago and it did nothing for me. My insulin dosage did not have to be adjusted in the least. That was a 2 month trial.