I've spoken to a lot of bulimics who've take Topomax, and all have said it helped significantly to reduce the urge to purge. They all said it helped, some significantly.

Sorry it's only second hand, but I hope it offers some hope for you. I have, though, also heard that you have to start very low, and increase very slowly. That will minimize the side effects, and the side effects have been bad for some of them. Only a couple stopped over them, but it's something else to keep in mind. (Although my former pdoc said taking bicarb with it helps with most of them.)