The only side effect that I have experienced with Lamictal (300 mg's a day), is memory loss. My short term memory is like Swiss cheese. Unless there was a major event, I can't remember what happened two weeks ago. Anything that is over a month ago, I will remember the event, but not which month it was in. I write everything down and I mean everything that I will have to remember at some point in time. I even have problems finding my way around my neighborhood if I'm under any amount of stress.
Other than that, the drug is great. I have no mania and or weight gain. It's really helped me a lot.