Phenethylamine is an organic compound and a natural monoamine alkaloid, a trace amine, and also the name of a class of chemicals with many members well known for psychoactive drug and stimulant effects. Phenylethylamine functions as a neuromodulator or neurotransmitter in the mammalian central nervous system. It is biosynthesized from the amino acid phenylalanine by enzymatic decarboxylation. In addition to its presence in mammals, phenethylamine is found in many other organisms and foods, such as chocolate, especially after microbial fermentation. It is sold as a dietary supplement for purported mood and weight loss-related therapeutic benefits; however, orally ingested phenethylamine experiences extensive first-pass metabolism by monoamine oxidase B (MAO-B), which turns it into phenylacetic acid. This prevents significant concentrations from reaching the brain in low doses.