Fen-Phen is an anti obesity oral medicine. It is a combination drug containing fenfluramine and phentermine. Fenfluramine is an anti obesity drug nearly similar to dexfenfluramine another weight loss drug. Whereas Phentermine another weight loss medication was also available in the market with many brand names including Phentrol for treatment of obesity. The combination was launched in the market as a miracle drug to reduce obesity. It was withdrawn from U.S. market in 1997 due to its alleged link with heart valve diseases.

Phentermine was approved in 1959 by the United States Food & Drug Administration. It was approved to be used as anti obesity drug. Fenfluramine was approved by the FDA to be used as a drug to reduce obesity in 1973.

FDA issued a Fen-Phen safety update in August 1997. This update stated that fenfluramine and phentermine has been associated with the development of serious cardiac valvular disease. It asked the Wayeth pharmaceutical, a subsidiary of American Home Products Corporation, the manufacturer of the drug Fen-Phen to add a black box warning on the label of he drug and patient package inserts related to valvular heart diseases and Pulmonary Hypertension. It restricted use of this drug only in people with significant obesity. It asked to not use this drug in people with minimal obesity.

It also stated that Phentermine and fenfluramine both were as single agents for short-term obesity treatment. The combination drug was being prescribed for obesity management on off-label basis for long-term treatment of obesity in patients.

This safety update was a result of reports by Mayo clinic released in July 1997. It found out 24 cases of cardiac valvular disease in women who were on this combination drug for an average of about 12 months. FDA received more similar reports. It has previously asked healthcare professional to report such case previously. This resulted in larger number of reporting related to severe side effects of this drug. FDA was working with other research agencies to determine the relation between valvular heart diseases and pulmonary hypertension with use of Fen-Phen.

Finally it came with the decision of withdrawing this drug from the market on 15th September. It asked manufacturers to voluntarily withdraw Fen-Phen along with another anti obesity drug Dexfenfluramine. Dexfenfluramine is manufactured for Interneuron Pharmaceuticals and marketed under the name of Redux by Wyeth Laboratories; a subsidiary of American Home Products Corp. American Home Products also manufactured Fenfluramine. Both companies agreed to voluntarily withdraw their drugs. But the other component of Fen-Phen namely Phentermine was not withdrawn from the market.

FDA received many reports of Fen-Phen Side effects even after its withdrawal. FDA issued another safety update in November 1997. FDA advised patients, who have taken this drug to consult their doctor. It decided that Centers for Disease Control and Prevention, the Food and Drug Administration, and the National Institutes of Health (all components of Department of Health and Human Services) would jointly issue interim recommendation for patients, who have used this drug in November issue of the Morbidity and Mortality Weekly Report (MMWR).