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November 1, 2004

No Evidence that Diet Drugs Work

The subtitle for this discussion of diet drugs could be “Statistially Significant but Clinically Trivial benefit - Too Often Toxic.” This phrase sums up what we know about the effectiveness and safety of the diet drugs.

Years ago, the FDA set the bar too low for the approval of diet drugs. In June 1968, FDA Medical Officer Robert O. Knox, MD, refused to approve the New Drug Application (NDA) for a particular diet drug. This disapproval touched off a dispute between the FDA and the drug’s manufacturer, A.H. Robbins, that eventually led to the drug’s approval and Dr. Knox’s transfer to another area within the FDA. His reason for not approving the drug: obesity is a chronic disease and, even if the drugs can reduce weight, there is no evidence that these drugs affect the course of the disease over the long term or that the consequences of obesity arer averted.[1]

The drug Dr. Knox refused to approve was fenfluramine (PONDIMIN), a drug that ultimately became the “fen” portion of the notorious “fen-phen” combination of diet drugs, fenfluramine was removed from the market on September 15, 1997.[2] These drugs caused heart valve damage and a potentially fatal adverse reaction of the lungs known as primary pulmonary hypertension.[3],[4]

Thirty years of experience with diet drugs has clearly vindicated Dr. Knox’s views. If his recommendation had been heeded in 1968, and the FDA had adopted a standard that required the demonstration of a health benefit from these drugs (rather than just weight loss), the public may have had better drugs, hundreds of millions of dollars would have been saved, and an immeasurable number of patients would have been spared serious harm and even death.

Prevention may be the best treatment for obesity. Our advice about losing weight and diet pills has been the same for 20 years: Eat less, exercise more. This approach to losing weight is slow but effective. The only one who profits from it is you. That’s why it isn’t sold.

  • Dorsen N., Weiner N., Astin A.A., et al. Investigation of Allegations Relating To The Bureau Of Drugs, Food and Drug Administration. 1977: Department of Health, Education, and Welfare. 279-344.
  • Food and Drug Administration. FDA Announces Withdrawal of Fenfluramine and Dexfenfluramine. 1997.
  • Abenhaim L., Moride Y., Brenot F., et al. Appetite-suppressant drugs and the risk of primary pulmonary hypertension. International Primary Pulmonary Hypertension Study Group. New England Journal of Medicine. 1996;335(9):609-616. PM:8692238.
  • Connolly H.M., Crary J.L., McGoon M.D., et al. Valvular heart disease associated with fenfluramine-phentermine. New England Journal of Medicine. 1997;337(9):581-588. PM:9271479.