Obese people who take an appetite suppressant for more than three months increase by 30 times their chances of developing primary pulmonary hypertension, a usually fatal condition affecting the arteries in the lungs.

The association between this rare condition and the family of appetite suppressants is alarming because the drugs are being prescribed in increasing numbers. Dexfenfluramine (Redux), for example, has only recently been approved for use in America.

Researchers from the International Primary Pulmonary Hypertension Study Group were alerted to a possible link after a cluster of patients in France suddenly developed the condition. All were taking derivatives of fenfluramine to control their weight.

The researchers compared 95 pulmonary hypertension patients with 355 recruits, selected to match the patients' sex and age.

They found that the risks of developing the condition escalated the longer the patient took the drug: those currently taking one of the drugs faced a 6.3 times increased risk; this rose to 10.1 times if the drug had been taken the previous year, and the risk increased to 23 times if the drug had been taken for longer than three months. Researchers say they do not know how the risks increase beyond that time because experience with the drugs has been limited, but they estimate the risk increases to more than 30 times if the drug is taken longer than three months by an obese person.

Risks worsened if the patient has a family history of pulmonary hypertension, if he or she is HIV positive, has cirrhosis, or uses cocaine or intravenous drugs.

In an accompanying editorial, JoAnn Mason from Harvard Medical School and Gerald Faich from the University of Philadelphia warn that obesity is the second leading cause of preventable death in the US, and that drug therapy is one of the few successful methods of losing weight

!AN Eng J Med, 1996; 335:9; 609-15.