 Subsequently, reports of severe side effects associated with heart valve abnormalities and an increased risk of pulmonary hypertension resulted in a decision to remove products containing fenfluramine from the U.S market, and then from other markets around the world.Dexfenfluramine inhibits serotonin reuptake, stimulating the release of serotonin.In 1996, dexfenfluramine became the first long-term treatment anti-obesity medication approved in the US; adverse effects observed during clinical trials included dry mouth, diarrhea and drowsiness.