Psychopharmacology
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Comparative Study
Importance of sex and relative efficacy at the mu opioid receptor in the development of tolerance and cross-tolerance to the antinociceptive effects of opioids.
Recent studies indicate that mu opioids are generally more potent and effective as antinociceptive agents in male than female rodents. ⋯ That comparable levels of morphine tolerance were obtained in males and females when the functional chronic morphine dose was taken into consideration suggests that the mechanism underlying tolerance is not sex-dependent. Sex differences in the effectiveness of buprenorphine and dezocine when administered acutely and during chronic morphine administration further suggest that these opioids have lower efficacy at the mu opioid receptor in females.