Fen-phen was an anti-obesity medication (an anorectic) which consisted of two drugs : fenfluramine and phentermine. Fenfluramine, and later a related drug , dexfenfluramine, was marketed by American Home Products, now known as Wyeth.
After reports of valvular heart disease and pulmonary hypertension primarily in women who had been undergoing treatment with fen-phen, the FDA requested its withdrawal from the market in September 1997.
The action was based on findings from doctors who had evaluated patients taking these two drugs with echocardiograms, a special procedure that can test the functioning of heart valves. These findings indicated that approximately 30 percent of patients who were evaluated had abnormal echocardiograms, even though they had no symptoms. This is a much higher than expected percentage of abnormal test results.
In July 1997, researchers at the Mayo Clinic and Mayo Foundation reported 24 cases of rare valvular disease in women who took the "fen-phen" combination therapy. FDA alerted medical doctors that it had received nine additional reports of the same type, and requested all health care professionals to report any such cases to the agency’s MedWatch program or to the respective pharmaceutical manufacturers.
Subsequently, FDA received 66 additional reports of heart valve disease associated mainly with "fen-phen." There were also reports of cases seen in patients taking only fenfluramine or dexfenfluramine. FDA requested that the manufacturers of fenfluramine and dexfenfluramine stress the potential risk to the heart in the drugs ’ labeling and patient package inserts. As of 1997, the FDA continued to receive reports of cardiac valvular disease in persons who have taken these drugs .