 The drug also acts as a norepinephrine releasing agent to a lesser extent, particularly via its active metabolite norfenfluramine.At high concentrations, norfenfluramine, though not fenfluramine, also acts as a dopamine releasing agent, and so fenfluramine may do this at very high doses as well.In addition to monoamine release, while fenfluramine binds only very weakly to the serotonin 5-HT2 receptors, norfenfluramine binds to and activates the serotonin 5-HT2B and 5-HT2C receptors with high affinity and the serotonin 5-HT2A receptor with moderate affinity.