Syntrix Pharmaceuticals announces the discovery that desmetramadol is a G-protein biased opioid receptor agonist. The results, published in Frontiers in Pharmacology show that desmetramadol, the active metabolite of tramadol, is as effective as morphine, oxycodone and fentanyl in eliciting G protein coupling at the human ? opioid receptor (MOR) involved in pain relief, but surprisingly, supra-therapeutic concentrations typical of overdose spare human MOR-mediated barrestin2 recruitment, the signaling pathway of the receptor thought to mediate lethal opioid-induced respiratory depression.