Along with the other previously "orphan" receptors GPR55 and GPR119, GPR18 has been found to be a receptor for endogenous lipid neurotransmitters, several of which also bind to cannabinoid receptors.
Zajedno sa drugim „orfanskim“ receptorima GPR55 i GPR119, za GPR18 je utvrđeno da je receptor za endogene lipidne neurotransmitere, nekoliko od kojih se takođe vezuju za kanabinoidne receptore.