Variability in simian motor and social behavior with alternating-day acetylmethadol

Monkeys receiving acetylmethadol thrice weekly were more active on dosing days, and less active on between-dose days, than while drug-free. Aggressive social behaviours increased significantly on drug-dosing days, while quiescent resting behaviors were much more common on between-dose days. Tolerance to these effects was modest, and the effects were not blocked by naltrexone. These subtle but potentially disruptive behavioral effects appear to parallel many of the actions of acetylmethadol in man.