Tachykinin peptides are one of the largest family of neuropeptides, so named due to their ability to rapidly induce contraction of gut tissue. Tachykinins excite neurons, elicit behavioural responses, are potent vasodilators and contract many smooth muscles. The tachykinin family is characterized by a common C-terminal sequence, Phe-X-Gly-Leu-Met-NH2 (where X can be either an aromatic or an aliphatic amino acid) and are ten to twelve residues long.

These peptides elicit their effects via the tachykinin receptors, of which there are three types in humans (NK1,2 and 3). There are two human tachykinin peptide genes in humans, TAC1 and TAC3. TAC1 encodes substance P and substance K while TAC3 encodes neurokinin B.

Antagonists of these receptors are promising candidates for classes of antidepressants, anxiolytics and antipsychotics.