TAR1 (Trace Amine Receptor 1) or TA1 is a receptor for trace amines. The receptor can be activated by endogenous trace amines as well as metabolites of the biogenic amine neurotransmitters. Trace amines are biogenic amines present in very low levels in mammalian tissues. Although some trace amines have clearly defined roles as neurotransmitters in invertebrates, the extent to which they function as true neurotransmitters in vertebrates has remained speculative. Trace amines are likely to be involved in a variety of physiological functions that have yet to be fully understood. Trace amine receptors are potential direct targets for drugs of abuse, including amphetamine and 3,4-methylenedioxymethamphetamine (MDMA).