Phentermine is a sympathomimetic amine that is used as an appetite suppressant. It is prescribed to obese patients and is one of the most popular anti-obesity drugs. It was one half of the Fen-phen anti-obesity drug, the other being fenfluramine. Fenfluramine was withdrawn from the shelves in 1997 after reports of heart valve disease and pulmonary hypertension. Phentermine should not be used by those who have a history of substance abuse or they suffer from glaucoma or high blood pressure.