According to health encyclopedia, the medicines that may cause you weight gain are:
Medicines for Diabetes such as Insulin and Sulfonylureas.
Antipsychotic medicines such as Haloperidol and Clozapine.
Antidepressant medicines such as Paroxetine and Sertraline.
Epilepsy medicines like Valproate and Gabapentin.
Steroid hormone medicines like Prednisone or Birth control pills.
Blood pressure reducing medicines like Propranolol and Metoprolol.