I'm sorry you've had such significant weight loss. I on the other hand have had significant weigh gain. It's not that appetite has increased or eating habits have changed. Quite the contrary in fact. I still stick to a low calorie/fat diet but have gained well over 75 lbs on Dilantin. I'm having quite the difficult time losing it as well. It seems that as fast as i lose the weight it just comes right back.

I've been on three different meds since my first siezures when i was 14. I've been on Depakote (AWFUL DRUG) Dilantin and Keppra (another horrifying drug) 

I've had issues with each drug honestly. Depakote just had no effect on my seizures. In fact my instances of having a seizure tripled while on that one. 

Keppra is just all wrong for me apparently. When i took that a few years ago after a rather nasty seizure in which i fell into a nightstand and drove my upper teeth through my lower lip leaving a massive and terribly unattractive scar, I was placed on it. I though i was going to die. In the 6 weeks i was on it my heartrate stayed at a constant 190bpm, i had awful dizzy spells. I literally had to crawl to the bathroom because i just could not stand up without falling down. My eyes twitched constantly as did other parts of my body. My vision was blurred and i could not talk to someone clearly because my words were horribly slurred. I nearly lost my job because of all the time i had to be out because i simply could not function properly. My hair was falling out in massive chunks,on top of this i was still having seizures, and all the doctors would say was oh give it time to normalize.....

After that awful experience i went back to the Dilantin. It has it's side effects too, but they seem to be less  dramatic than any others i have had. The truly annoying ones are the weight gain, the swelling gums and increased enamel wear on my teeth. Both manageable though. I do have pretty rough memory loss. I honestly do not know if that's perhaps some effects of the grand mal seizures or if it's the drug.  Some days are worse than others. But it gets to be pretty bad when you go into the bathroom because you have to pee and when you walk in there you literally forget why you're there. I have days when i can't think of simple words and it's very frustrating. But i would rather have these side effects than to give up my one great joy....I love to drive, and Dilantin has been the ONLY meds that have completely stopped my seizures and allowed me to get my license back.  For that I am indescribably grateful and would pay any price to have that priviledge.