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 non-classical metabolic derivatives of phenylalanine and tryptophan – and related psychostimulants, particularly amphetamine and methamphetamine. In 2004 it was shown that in mammals TAAR1 is also a receptor for thyronamines, decarboxylated and deiodinated metabolites of the thyroid hormones. Based upon evidence in mammals, it has been proposed that TAAR2–TAAR9 may have a function as olfactory receptors for volatile amines.