Phenylethylamine (11.1) or, more strictly, 2-phenylethylamine is the structural parent of the amphetamines, but, unlike them, occurs naturally. The human body makes it by decarboxylation of phenylalanine, albeit in very small amounts; it acts in the brain in a similar way to amphetamines by releasing the neurotransmitters dopamine and norepinephrine. Phenylethylamine levels are low in depressed people; conversely, physical exercise raises phenylethylamine levels, suggesting a cause of “runner’s high”. Signi†cant amounts of phenylethylamine are found in chocolate, leading to speculation that eating chocolate can make you fall in love, but rapid oxidation of phenylethylamine by monoamine oxidase enzymes in the liver will prevent that.