CNR1 and Arthritis: Palomares et al. [12] showed that Δ9-Tetrahydrocannabinolic acid (Δ9-THCA-A), the precursor of Δ9-THC, can act as an orthosteric CB1R agonist; in vivo, Δ9-THCA-A reduced arthritis in collagen-induced arthritic mice, preventing the infiltration of inflammatory cells, synovium hyperplasia, and cartilage damage.