<unk>  exhibits partial agonist and antagonist activity at the μ-opioid receptor, as well as partial agonist activity at the κ-opioid receptor (Ki = 2.5 nM; EC50 = 57 nM; Emax = 57%). Stimulation of these receptors on central nervous system neurons causes an intracellular inhibition of adenylate cyclase, closing of influx membrane calcium channels, and opening of membrane potassium channels. This leads to hyperpolarization of the cell membrane potential and suppression of action potential transmission of ascending pain pathways. Because of its κ-agonist activity, at analgesic doses<unk>  increases pulmonary arterial pressure and cardiac work. Additionally, κ-agonism can cause dysphoria at therapeutic or supertherapeutic doses; this gives<unk>  a lower potential for abuse than other opioid drugs.
Butorphanol
Levorphanol
Morphine
Oxymorphol
Hydromorphone
Oxymorphone
Noroxycodone
Nalorphine