NK1R (The tachykinin receptor 1,substance P receptor) is a G protein coupled receptor found in the central nervous system and peripheral nervous system. The endogenous ligand for this receptor is Substance P, although it has some affinity for other tachykinins. Tachykinins are a family of neuropeptides that share the same hydrophobic C-terminal region. Substance P is the most researched and potent member of the tachykinin family. SP binds to all three of the tachykinin receptors, but it binds most strongly to the NK1 receptor.