--many of the anti-epileptics used for neuropathy, and a number of the other meds, including some of the anti-depressants, tend to cause carb-craving and appetite increases, so weight gain, both due to that and in the case of some of the meds fluid retention as well, are fairly common side effects.

Among the anti-epileptics, a notable exception to this pattern is Topomax, which more people have reported wight loss with; the why's of that are not known, though.