Weight gain is a side effect of a number of anti-seizure medications, but the mechanisms as to how it happens are not completely understood.

Two leading theories for Neurontin/Lyrica--both are drugs metabolized primarily by the kidneys (not the liver, as most drugs are) and excreted almost whole; there's some indication that it may alter the fluid retention balance as a result, causing greater fluid retention ("water weight"). There's also the "hibernation" effect--these anti-seizure drugs work by increasing the concentration of inhibitory neurotransmitters in the central nervous system (so inappropriate neural signals don't overly propogate), and this seems to make the body feel it should add on mass for lean times, so one gets carb cravings. (There's probably an effect on the pineal gland--these meds can exacerbate those who have a degree of seasonal affective disorder.)


Of course, the fact that fatigue and lassitude are common side effects of these meds also may simply cause people to be less active, and that can make one gain weight all by itself.

I've put on about 20 lbs. in the nearly four years since this all started--at least 18 of them around my gut. I would like to think some of the gain is muscle mass from weightlifting, but I do know I don't get the aerobic exercise I used to. I'm currently trying to increase my walking regimen and eat less, as my weightlifting is almost nonexistent with the ongoing right shoulder/right cervical spine radiculopathy problem. (Of course, the more I walk, the hungrier I get.)