Yes, weight gain is a possible side effect for gabapentin (brand name Neurontin).
The incidence of weight gain with gabapentin varies by product:
- Immediate release gabapentin: 2-3%
- Extended release gabapentin (e.g. Gralise, Horizant): 1.9-5%
In those who do experience weight gain, the average increase is around 16 pounds according to the prescribing information for the drugs (Gabapenin, Gralise, Horizant). The weight gain appears to be closely associated with another gabapentin side effect, appetite increase. It is not fully understood whether potential weight gain is solely due to an increased appetite or the side effect occurs via other mechanisms.
Lastly, the weight gain associated with gabapentin appears to be dose related, meaning higher doses increase your risk of weight gain.