History of Phentermine

History of Phentermine

Phentermine is the most commonly prescribed prescription appetite suppressant, accounting for 50% of the prescriptions. Part of this reason is because it’s significantly cheaper than the other major FDA-approved diet drugs, Meridia and Xenical.

Phentermine first received approval from the Food and Drug Administration (FDA) in 1959 as an appetite suppressant for the short-term treatment of obesity.

Phentermine resin became available in the United States in 1959 and Phentermine Hydrochloride in the early 1970s.

In the US, Phentermine is currently sold under the brand names Ionamin® (Medeva Pharmaceuticals) and Adipex-P® (Gate Pharmaceuticals). It is also available as a generic medication, known as ‘phentermine’.

Previously, it was sold under the name Fastin® (formerly produced by King Pharmaceuticals for SmithKline Beecham). In December 1998, SK-Beecham withdrew Fastin from the market.

As Phentermine is an older drug, no new efficacy trials have been conducted. The one notable exception, are several trials on the combination of Phentermine and Fenfluramine in the early and mid 1990s.

FEN-PHEN (or Phen-Fen) and Dexfen-Phen – two passing trends

Fen-Phen refers to the combination, or cocktail, of Fenfluramine or Pondimin (the “Fen”) and Phentermine (the “Phen”). Fenfluramine received FDA approval in 1973 for the short-term treatment of obesity. Together, Phentermine and Fenfluramine produced a powerful diet drug cocktail.

The FDA never approved the Fen-Phen combination, but once the agency has approved a drug, doctors may prescribe it at will. Their use, together, was considered “off-label”.

In 1992, Dr. Michael Weintraub of the University of Rochester and several colleagues published a study citing Fen-Phen as a more effective method than dieting or exercise in reducing the weight of the chronically obese. Even better – Fen-Phen, unlike an earlier generation of speed-laden diet drugs, seemed to be without immediate side effects.

The Fen-Phen cocktail became an overnight sensation. 1996 saw 6.6 million prescriptions of Fen-Phen in the U.S.

Dexfen-Phen refers to the combination, or cocktail, of Dexfenfluramine or Redux (the “Dexfen”) and Phentermine (the “Phen”). Dexfenfluramine received FDA approved in 1996 for use as an appetite suppressant in the management of obesity.

Like Fen-Phen, Dexfen-Phen, too, became an overnight sensation.

Neither combination, however, was ever tested for safety ….

By the summer of 1997, the Mayo Clinic reported 24 cases of heart valve disease. All 24 people had taken the Fen-Phen cocktail. The cluster of unusual cases of heart valve disease in Fen-Phen users suggested a co-relation between Fen-Phen use and heart valve disease.

On July 8, 1997 the FDA issued a Public Health Advisory to report the Mayo findings (which were later published in the August 28 issue of the New England Journal of Medicine). Please click here to read the FDA Health Advisory.

The FDA continued to received additional reports of heart disease, including reports from patients who had taken only Fenfluramine or Dexfenfluramine.

Further evaluations of patients taking Fenfluramine or Dexfenfluramine, showed that approximately 30% had abnormal valve findings. This figure is much higher than expected for abnormal test results and suggest Fenfluramine and Dexfenfluramine as the likely causes of Primary Pulmonary Hypertension (PPH) and valvular heart disease.

The FDA responded promptly to the alarming findings, and in September 1997, requested drug manufacturers to voluntarily withdraw Fenfluramine and Dexfenfluramine. At the same time, the FDA recommended that patients using either Fenfluramine or Dexfenfluramine stop taking them. To view the FDA September 1997 statement regarding the withdrawals, please click here.

The FDA did not, however, request the withdrawal of the third drug involved in the cocktails, Phentermine.


The newest cocktail involving Phentermine is “Phen-Pro” – the “Pro” standing for Prozac. Any one of the following antidepressants: Zoloft, Celexa, Luvox, Trazadone or Effexor may be used in lieu of Prozac.

The use of the antidepressant in the Phen-Pro cocktail is unrelated to depression. The cocktail is necessary because the effects of Phentermine, when used alone, lessen over time. The Phen-Pro cocktail enables Phentermine to work better and for a longer period of time. The cocktail does not appear to cause the problems that resulted from the usage of Fen-Phen.

The combination of Phentermine and Prozac is considered an “off-label” use, meaning that the FDA, who often voice concerns regarding the mixing/combining of medications, does not approve it. However, once the agency has approved a drug, doctors may prescribe it at will.

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