Two very popular diet pills taken by millions of women have been linked to a serious heart ailment.

Doctors at the Mayo Clinic, Rochester, Minnesota, found that 24 women taking fen phen, a popular combination of the dietary pills fenfluramine and phentermine, developed an unusual and serious heart valve problem. Eight of them also had a potentially fatal condition in which the arteries that supply blood to the lungs constrict.

Nine other women who do not attend the Mayo clinic have also reported having the condition.

The extent of the problem is not known because the discoveries were made in the course of normal medical practice, and not in clinical trials.

The American Food and Drug Administration has issued a warning to doctors across the United States about prescribing the combination pills, although a direct link between the drugs and the condition has not yet been established. Each of the drugs has been cleared by the FDA to be taken for short periods by people who are severely obese, but the administration never sanctioned their use as a combination drug.

Despite this, doctors in the US wrote around 18 million prescriptions for fen phen last year alone (New York Times, July 9, 1997).