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).