Kaczocha M, et al. - Whether administration of intrathecal morphine attenuates postoperative pain, was investigated. Researchers also determined the impact of intrathecal morphine upon circulating levels of the weakly analgesic endocannabinoids, anandamide (AEA) and 2-arachidonoylglycerol (2-AG), and the related lipids palmitoylethanolamide (PEA) and oleoylethanolamide (OEA). Reduced postoperative pain was noted post-total knee arthroplasty in patients who received intrathecal morphine. Also, a negative modulation of the endocannabinoid tone by activation of central opioid receptors suggested that potent analgesics could reduce the stimulus for production of peripheral endocannabinoids. For the fist time, the existence of rapid communication between the central opioid and peripheral endocannabinoid systems in humans was documented.