 Fenfluramine's anorectic effect is achieved through an increase in serotonin levels, imparting a sensation of fullness, which leads to a lower intake of food.Fenfluramine was sold as a racemic mixture of two enantiomers, dexfenfluramine and levofenfluramine.In 1994, sales of the combination drug Fen-phen (fenfluramine and phentermine) increased dramatically, as this combination produced substantial and apparent synergistic effect in promoting weight loss.