Antiopiate

That is, the location of heroin use can serve as a conditioned stimulus for the antiopiate response. When the user injects the drug in a different location, the well-developed antiopiate response does not occur […]

Source: wiktionary

Cholestyramine, however, may exert effects different from decreasing the enterohepatic circulation of bile acids including the release of endogenous antiopiates (e.g., cholecystokinin) that may result in a decrease in the perception of pruritus.

Source: wiktionary