In 1959, phentermine first received approval from the United States
FDA as an appetite-suppressing drug. Phentermine hydrochloride then
became available in the early 1970s. It was previously sold as Fastin
from King Pharmaceuticals for SmithKline Beecham, but in 1998, it was removed from the market. Medeva Pharmaceuticals sells the name brand of phentermine called Ionamin and Gate Pharmaceuticals
sells it as Adipex-P. Phentermine is also currently sold as a generic.
Since the drug was approved, almost no clinical studies have been
Phentermine was marketed with fenfluramine as a combination appetite suppressant and fat burning agent under the popular name Fen-Phen.
In 1997, after 24 cases of heart valve disease in Fen-Phen users,
fenfluramine and dexfenfluramine were voluntarily taken off the market
at the request of the FDA. Studies later proved nearly 30% of people taking fenfluramine or dexfenfluramine had abnormal valve findings.
Phentermine is still available by itself in most countries, including the US. However, because it is similar to amphetamine, it is classified as a controlled substance in many countries. Internationally, phentermine is a schedule IV drug under the Convention on Psychotropic Substances. In the United States, it is classified as a Schedule IV controlled substance under the Controlled Substances Act. In contrast, amphetamine preparations are classified as Schedule II controlled substances.
Phentermine is being studied in combination with other medications
for obesity. The first such combination is the appetite suppressant phentermine/topiramate (Qsymia formerly Qnexa). In 2012, the FDA approved its sale in the United States.