CNR1 and rheumatoid arthritis: Clinical studies have demonstrated that CB1 and CB2 receptor mRNA and proteins are expressed in the synovia of OA and RA patients and that the endocannabinoids 2-AG and AEA are present in the synovial fluid of these patients, but not in the synovial fluid of individuals without joint symptoms (Richardson et al. 2008), suggesting an upregulation of the EC system to counteract inflammation and cartilage degradation in OA patients.