Cyproheptadine (Periactin) is an antihistamine that can stimulate appetite and lead to weight gain. It is generally safe when taken at the recommended dosage, but it can cause side effects such as drowsiness, dry mouth, dizziness, and nausea. These side effects are usually reversible once the medication is stopped. It is important to consult with a healthcare professional before starting any new medication to ensure it is appropriate for you and to monitor for any potential interactions with other medications you may be taking.