GPR55 (G protein-coupled receptor 55) is a G protein-coupled receptor that in humans is encoded by the GPR55 gene. GPR55, along with GPR119 and GPR18, have been implicated as novel cannabinoid receptors. GPR55 is activated by the plant cannabinoids 9-THC and cannabidiol, and the endocannabinoids anandamide, 2-AG, noladin ether in the low nanomolar range. Recent research suggests that lysophosphatidylinositol and its 2-arachidonoyl derivative may be the endogenous ligands for GPR55, and the receptor appears likely to be a possible target for treatment of inflammation and pain as with the other cannabinoid receptors. The physiological role of GPR55 is unclear. GPR55 has been proposed as a new potential drug target for the treatment of diabetes, Parkinson’s disease, neuropathic pain, and cancer.