Abstract: AimTo investigate the effects of intragastric administration of thenorphine (Then) on behavioral sensitization to morphine (Mor) in mice.MethodsLocomotor activity was detected after intragastric administration of thenorphine or co-administration of thenorphine with Mor in mice. Mice were induced to be behaviorally sensitive to Mor, and were given the combination of Mor and thenorphine to observe the effects of thenorphine on the development, transfer and expression of Mor-induced behavioral sensitization. ResultsA single intragastric administration of thenorphine (1.25-5.0 mg·kg^-1) dose-dependently inhibited the locomotor activity in mice (P<0.01) and the effects of thenorphine on locomotor activity developed tolerance after repeated administration. Co-administration of thenorphine effectively inhibited Mor-induced hyperactivity (P<0.05) and the development, transfer, expression of Mor-induced behavioral sensitization in mice (P<0.05 or P<0.01). ConclusionThenorphine was shown to suppress the central nervous system and may be effective against the abuse and addiction to opioids.