A Possible Genetic Mechanism Underlying Individual and Interstrain Differences in Opioid Actions: Focus on the Mu Opioid Receptor Gene

: Individual differences in responses to opioids limit effective pain treatment with these drugs. Identifying the mechanism could help to improve the analgesic effects of them. Since the molecular cloning of the mu opioid receptor (muOR) gene, substantial advances in opioid research have been made, including the discoveries that muOR plays a mandatory role in the analgesic effects of opioids and that the sequence of the muOR gene varies from one individual to another. It is conceivable that the differences in the muOR gene cause individual differences in opioid actions. The present review summarizes the recent advances made in research on human and mouse muOR genes and proposes that the variances in the 3′ untranslated region (39-UTR) of the muOR gene might participate in the variability of the opioid response.