Two commonly prescribed weight-loss medications are fenfluramine and dexfenfluramine. They are neurotoxins which destroy the nerve cells in the brain which produce serotonin, a brain chemical responsible for subtle enhancements of well-being and also influencing appetite. The risk of these drugs producing disabling and potentially lethal primary pulmonary hypertension as a side effect is increased at least 30 times over the normal rate (2 in 1 million persons).
A new anti-obesity pill, sibutramine, may not have these side effects, but doctors state that prevention of overweight, not treatment afterward, is preferable to dieting.