First approved almost half a century ago in 1959 as an appetite suppressant, phentermine is sold under a variety of brand names including Ionamin and Adipex-P as well as under its generic name.

Phentermine is a sympathomimetic amine, which is similar to an amphetamine. It is also known as an "anorectic" or "anorexigenic" drug. It stimulates the central nervous system (nerves and brain), which increases your heart rate and blood pressure, and it suppresses your appetite.

During the 1990s, phentermine was commonly used with another medication called Fenfluramine hydrochloride in a combination referred to as Fen-phen.

In 1997, this combination became the center of a storm, and fenfluramine and dexfenfluramine were taken off the market for possibly causing heart valve damage.

Because of possible adverse effects and contraindications for use, phentermine is generally used to treat obesity only for a brief period of time.

At an earlier time, a number of other versions of phentermine also were approved for sale in the U.S., including Fastin, Obestin-30, Oby-Trim. None of these are on the FDA's list of drugs currently approved for U.S. sale.