α-1-Acetylmethadol and its N-demethylated metabolites have potent opiate action in the guinea pig isolated ileum

α-1-Acetylmethadol (LAM) and its N-demethylated metabolites α-1-noracetylmethadol (NAM) and α-1- dinoracetylmethadol (NNAM) exhibited opiate-like actions invitro by depressing the electrically induced twitch of the longitudinal muscle of the guinea pig ileum. These effects were reversed by the opiate antagonist naloxone. The effect of both NAM and NNAM was approximately 15 times greater than LAM. The 50 percent inhibitory concentrations of the metabolites were well below those levels in plasma reported for man. The long duration of action of LAM as an opiate substitute is most likely due to the conversion to its metabolites.