I was on it for headaches almost 10 years ago. I was on a very high does, even for a seizure patient and have been off it for quite a few years. I gained weight very quickly with it and haven't been able to loose any since. I recently found this out ... Anticonvulsants tend to cause hyperinsulinemia (elevated insulin in the blood) and increased appetite leading to weight gain. Hyperinsulinemia also results in increased testosterone, which causes a risk to women on these medications for development of Polycystic Ovary Syndrome (POS). Polycystic ovary syndrome can cause weight gain, male pattern baldness, increased facial hair, skin tags, acne, infertility, high blood pressure, abnormal lipid levels, and heart disease.

Seizure disorder studies showed that patients taking anticonvulsants who had either a normal or below normal body mass index had the most severe weight gain.
http://www.netnutritionist.com/fa12.htm

I gain 60 lbs it was awful , got off it quick . I am now on Keppra and it works well