Nalorphine

Nalorphine (INN) (brand names Lethidrone, Nalline), also known as N-allyl-normorphine, is a mixed opioid agonist–antagonist with opioid antagonist and analgesic properties. It was introduced in 1954 and was used as an antidote to reverse opioid overdose and in a challenge test to determine opioid dependence. It acts at two opioid receptors — the μ-opioid receptor (MOR) where it has antagonistic effects, and at the κ-opioid receptor (KOR) (K_i = 1.6 nM; EC₅₀ = 483 nM; E_max = 95%) where it exerts high-efficacy partial agonist/near-full agonist characteristics. Nalorphine was the second opioid antagonist to be introduced, preceded by nalodeine (N-allylnorcodeine) in 1915 and followed by naloxone in 1960 and naltrexone in 1963. Due to potent activation of the KOR, nalorphine produces side effects such as dysphoria, anxiety, confusion, and hallucinations, and for this reason, is no longer used medically.