Norbinaltorphimine dihydrochloride is a potent and selective κ opioid receptor antagonist. IC50 & Target: κ opioid receptor^[1] In Vitro: Norbinaltorphimine reversibly antagonize the effects of κ agonists with pA2 values of 10.2-10.4. Norbinaltorphimine is much less potent as an antagonist at μ and δ receptors, pA2 values are 7.4-7.6 and 7.6-7.8, respectively^[1]. In Vivo: Norbinaltorphimine has weak and inconsistent effects on THC-induced taste avoidance in adolescent rats in that Norbinaltorphimine both attenuates and strengthens taste avoidance dependent on dose and trial. Norbinaltorphimine has limited impact on the final one-bottle avoidance and no effects on the two-bottle preference test. Interestingly, Norbinaltorphimine has no effect on THC-induced taste avoidance in adult rats as well^[2]. Norbinaltorphimine pretreatment significantly attenuates stress-induced reinstatement of nicotine-CPP, but has no effect on nicotine-primed reinstatement^[3].