Phentermine is a sympathomimetic amine similar to amphetamine. Also known as anorectic/anorexigenic drug. Phentermine is one of the most widely used prescribed diet pill for the treatment of obesity. html “>Phentermine is one of two drugs in the Fen-phen anti – obesity medication, the other being fenfluramine or dexfenfluramine. Phentermine was first approved by the FDA in 1959 as an appetite suppressant for treatment of obesity. Phentermine is currently sold under the brand names Iona