Drugs that stimulate the appetite are known as orexigenics, according to Medical Dictionary. Commonly used orexigenics include antidepressants, antipsychotics, anabolic agents and cannabinoids. They may be used to treat loss of appetite in geriatric patients, the terminally ill, and patients undergoing chemotherapy, according to the American Association of Family Physicians.
Several mood-altering drugs are prescribed for their appetite-increasing side effects, as reported by MedScape. Cannabinoids such as nabilone and dronabinol are FDA-approved to treat loss of appetite associated with wasting disease or cachexia, notes MedlinePlus. Other drugs used to treat anorexia include antipsychotics such as olanzapine and risperidone. Weight gain is also a known side effect of the antidepressant drug mirtazapine. Finally, anabolic agents such as human growth hormone and testosterone have been demonstrated to facilitate weight gain.