Trace amine-associated receptors (TAARs), sometimes referred to as trace amine receptors (TAs or TARs), are a class of G protein-coupled receptors that were discovered in 2001.TAAR1, the first of six functional human TAARs, has gained considerable interest in academic and proprietary pharmaceutical research due to its unique role as the endogenous receptor for trace amines – which are trace metabolic derivatives of phenylalanine and tryptophan – and related psychostimulants, particularly amphetamine and methamphetamine. In 2004, it was shown that mammalian TAAR1 is also a receptor for thyronamines, which are decarboxylated and deiodinated metabolites of thyroid hormones.TAAR2–TAAR9 function as olfactory receptors for volatile amines in vertebrates.