Thienorphine

Thienorphine is a very potent, extremely long-acting, orally-active opioid analgesic with mixed agonist–antagonist properties which was developed by the Beijing Institute of Pharmacology and Toxicology as a potential treatment for opioid dependence. It is a high-affinity, balanced ligand of the μ- (K_i = 0.22 nM), δ- (K_i = 0.69 nM), and κ-opioid receptors (K_i = 0.14 nM), behaving as a partial agonist of the μ- (E_max = 19%–28%) and κ-opioid receptors (E_max = 65–75%) and as an antagonist of the δ-opioid receptor. It also possesses relatively low affinity for the nociceptin receptor (K_i = 36.5 nM), where it acts as an antagonist.