I have been on Topamax/Topiramate for a very long time, maybe 7 years or so, and tolerate it very well. Before I started on Topamax I was having migraines so severe that I could not function. I often ended up crying on the bathroom floor, throwing up. It was awful.
Once I started taking Topamax, I still had/have frequent migraines (about 17 days out of the month), but now I can function with them. They aren't quite as severe, and I don't throw up anymore.
The only side effects that I have are that I am freezing all the time, and I don't sweat. Freezing isn't listed on the side effects, but several people I know that also take Topamax also experience the same thing. I simply can't get warm. As for sweating, I don't sweat, ever. I've never been a person to sweat much; in fact, I don't wear deodorant, but now I don't sweat at all, even in our Texas summers. As for the brain fog, I only experience that for a couple of weeks whenever I change the dose of Topamax. Once my body adjusts to the new dose, I'm fine.
Now I take 300mg of Topamax daily, and I also get Botox injections every 3 months. With the Botox, I'm down to about 20 migraines every 3 months. That's a lot better than 17 a month. It's still not great, but it's an improvement, and with the Topamax I can at least function when I have one (most of the time).
I hope your son finds relief. Migraines are awful.