The chances of detecting a valve problem were related to the length of time from drug cessation. Valve problems were detected at twice the rate among patients who had stopped treatment less than eight months before their echocardiogram compared to those who had been off the medicine for longer than eight months. It has been estimated that in 1996, the total number of prescriptions for dexfenfluramine or fenfluramine and phentermine in the United States exceeded 18 million. The diet products containing fenfluramine and dexfenfluramine were taken off the market following reports that showed a link between diet drugs and damage to the heart valves. If the heart valve is damaged it either cannot open properly or fails to close all the way, letting blood leak backward.
Many healthy adults have very mild backward leakage of blood through the valve.
Severe heart valve damage, however, can be life-threatening. This latest study looked at the prevalence and severity of valve disease in 223 patients, recruited from 26 centers in 15 states, who had taken dexfenfluramine for an average of seven months. Those patients were compared to a control group of 189 people who did not take the diet drug which, in part, reduces a person's appetite by affecting serotonin, a chemical in the brain that makes people feel full. However, the frequency is not very high and the severity is usually mild. It is important to remember that no study yet has looked into the long-term effects.