Nalorphine (INNTooltip International Nonproprietary Name; also known as N-allylnormorphine; brand names Lethidrone and Nalline) is a mixed opioid agonist–antagonist with opioid antagonist and analgesic properties.

[4] 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.

[3] Due to potent activation of the κ-opioid receptor, nalorphine produces side effects such as dysphoria, anxiety, confusion, and hallucinations, and for this reason, is no longer used medically.

[2][3][5] Nalorphine acts at two opioid receptors — the μ-opioid receptor (MOR) where it has antagonistic effects, and at the κ-opioid receptor (KOR) (Ki = 1.6 nM; EC50 = 483 nM; Emax = 95%) where it exerts high-efficacy partial agonist/near-full agonist characteristics.

[7] More recently, it has become much more commonplace to use ethyl chloroformate instead of cyanogen bromide for the Von Braun degradation demethylation step.