By oral route, phenylethylamine's half-life is 5–10 minutes;[1] endogenously produced PEA in catecholamine neurons has a half-life of roughly 30 seconds.[2] It is metabolized by phenylethanolamine N-methyltransferase,[2][29] MAO-A,[9] MAO-B,[8] semicarbazide-sensitive amine oxidases (SSAOs),[30] aldehyde dehydrogenase,[31] and flavin-containing monooxygenase 3.[32] N-methylphenethylamine, an isomer of amphetamine, is produced in humans via the metabolism of phenethylamine by phenylethanolamine N-methyltransferase.[2][28][29] When the initial phenylethylamine brain concentration is low, brain levels can be increased 1000-fold when taking a monoamine oxidase inhibitor (MAOI), particularly a MAO-B inhibitor, and by 3–4 times when the initial concentration is high.[33] β-Phenylacetic acid is the primary urinary metabolite of phenethylamine and is produced via monoamine oxidase metabolism and subsequent aldehyde dehydrogenase metabolism.[7] In humans, phenylacetaldehyde is the intermediate product which is produced by monoamine oxidase and then further metabolized into β-phenylacetic acid by aldehyde dehydrogenase