 The mean elimination half-lives of its enantiomers have been found to be 19 hours for dexfenfluramine and 25 hours for levfenfluramine.Norfenfluramine, the major active metabolite of fenfluramine, has an elimination half-life that is about 1.5 to 2 times as long as that of fenfluramine, with mean values of 34 hours for dexnorfenfluramine and 50 hours for levnorfenfluramine.Fenfluramine is a substituted amphetamine and is also known as 3-trifluoromethyl-"N"-ethylamphetamine.