Description_x000D_ Biochem/physiol Actions_x000D_ GAT229 is the S-(-)-enantiomer of GAT211, a positive allosteric modulator (PAM) of cannabinoid CB1 receptor signaling that was found to amplify the therapeutic effect of endocannabinoids without the negative side effects of psychoactivity or tolerance. GAT229 was found to be a potent, Gαi/o-biased CB1 PAM without intrinsic activity, while the R-(+)-enantiomer, GAT228, was found to be an unbiased CB1 allosteric agonist. In radioligand binding assays, both GAT228 and GAT229 behaved as PAMs of orthosteric ligand binding, with GAT229 exhibiting higher potency and efficacy. Allosteric CB1R activation by GAT211 and its enantiomers could be a better therapeutic strategy for enhancing endogenous cannabinergic activity than targeting endocannabinoid-degrading enzymes with small-molecule inhibitors, with a lower likelihood of tolerance and dependence.