Weight gain can happen with long-term use of Phenytoin, but gaining 40 kg suggests that lifestyle factors or other metabolic issues may also be contributing, so it is important to address weight in a structured and safe way. Supplements like Garcinia Cambogia are generally not recommended because their benefits are uncertain and they may interact with medicines or affect the liver, which is important to monitor when taking seizure medications. Since you have been seizure-free for three years, it is a good time to consult your neurologist to review whether your medication dose can be adjusted or gradually reduced, which may help with weight, while also focusing on a balanced diet, regular exercise, and possibly guidance from a nutritionist. Avoid starting any over-the-counter supplement without medical advice, as maintaining seizure control safely should remain the top priority.