Fen Phen or Pondimin (generic name: fenfluramine) is a popular appetite suppressant drug that was prescribed to people wishing to lose weight. In medical studies, Fen Phen and Redux (generic name: dexfenfluramine) are linked to heart valve disease and primary pulmonary hypertension.

In 1997, the Food and Drug Administration (FDA) asked American Home Products (AHP), the makers of Pondimin and Redux, to withdraw its popular anti-obesity drugs from the market. AHP manufactured Pondimin and an AHP subsidiary, Wyeth-Ayerst Laboratories, manufactured Redux for Interneuron Pharmaceuticals.

The FDA made public findings from doctors evaluating patients who took fenfluramine and dexfenfluramine with echocardiograms. The FDA reported that approximately 30 percent had abnormal echocardiograms, even though they had no symptoms. This is percentage is much higher than expected.

Additionally, a Mayo Clinic study published in the New England Journal of Medicine on August 28, 1997 suggested that as high as one third of a sampling of Fen-Phen weight-loss patients had evidence of heart valve disease. The study found no other known reason for valve disease in these patients.

In addition to heart valve disease, the use of fenfluramine and dexfenfluramine has been found to increase the risk of developing primary pulmonary hypertension (PPH). PPH is a rare disease that causes the progressive narrowing of the blood vessels of the lungs. Studies estimate that treatment with certain appetite suppressant drugs tends to increase the chances of developing PPH by approximately 25 to 30 percent.