Buspar is supposed to be weight neutral, for what it's worth. I've never heard anyone say he/she gained from it.

PROZAC, though, is known to cause weight gain. Yes, Risperdal is also known to cause weight gain, but don't overlook the Prozac. You didn't mention your dose, nor how long you've been on it, but all the SSRIs tend to cause weight gain, because of their effect on the serotonin receptors in the gut that control both appetite and motility.

It's great that you're getting treatment for your ED, and I think this is a concern to take up wiht your doctor. One option that helps a lot of people is taking Topomax along with the drug that's causing weight gain. The rule with Topomax, to avoid side effects, is to start VERY low, and to go VERY slowly in titrating up.

Good luck.