Nalodeine, also known more commonly as N-allylnorcodeine, is an opioid antagonist (specifically, an antagonist of the μ-opioid receptor) that was never marketed but is notable as the first opioid antagonist to be discovered. It was first reported in 1915, and this was followed by the clinical introduction of nalorphine (N-allylnormorphine) in 1954, naloxone (N-allyloxymorphone) in 1960, and naltrexone (N-methylcyclopropyloxymorphone) in 1963. Nalmefene (6-desoxy-6-methylene-naltrexone), another structurally related opioid antagonist derivative, was also subsequently introduced, in 1996. In animals, nalodeine both reverses morphine- and heroin-induced respiratory depression and acts as a respiratory stimulant in its own right (i.e., when given alone). Similarly to nalorphine, nalodeine has