Norfenfluramine, or 3-trifluoromethylamphetamine, is a drug of the amphetamine family which behaves as a serotonin and norepinephrine releasing agent and potent 5-HT_2A, 5-HT_2B, and 5-HT_2C agonist. The action of norfenfluramine on 5-HT_2B receptors on heart valves leads to a characteristic pattern of heart failure following proliferation of cardiac fibroblasts on the tricuspid valve, known as cardiac fibrosis. This side effect led to the withdrawal of fenfluramine as an anorectic agent worldwide, and to the withdrawal of benfluorex in Europe, as both fenfluramine and benfluorex form norfenfluramine as an active metabolite.