Fenfluramine binds 5-hydroxytryptophan.

Fenfluramine, an anorexigenic drug, lowers serotonin (5-hydroxytryptamine) and 5-hydroxyindoleacetic acid levels in brain, spinal fluid, and blood, and has been used as a treatment for autism. Fenfluramine's mode of action is unknown. We present evidence from chromatography and nuclear magnetic resonance spectroscopy that fenfluramine selectively binds the serotonin and 5-hydroxyindoleacetic acid precursor, 5-hydroxytryptophan. The mode of binding may have general applications for the understanding of drug activity, receptor binding, and for the design of specific antagonists to aromatic compounds.