Acetylmethadol (INN), also known as methadyl acetate (USAN), is a synthetic opioid analgesic. It is a racemic mixture of alphacetylmethadol (α-acetylmethadol) and betacetylmethadol (β-acetylmethadol), which are in turn racemic mixtures of levacetylmethadol (LAAM; L-α-acetylmethadol) and D-α-acetylmethadol and L-β-acetylmethadol and D-β-acetylmethadol, respectively. Hence, acetylmethadol has four possible optical isomers. All of these isomers have been shown to partially or fully substitute for the discriminative stimulus effects of heroin in rats, and thus it can be inferred that, in addition to LAAM which is used clinically as such, they are all likely to be active opioid analgesics in humans.