Our study also suggests that there may be differences between male and female patients regarding the effects of genetic variation in the ABCB1 gene. Men with the minor TT allele had higher β-endorphin levels than men with the major CC allele but the reverse was true for women. Sia and co-workers [52] demonstrated a trend towards a higher risk of postoperative pain in women with the T-allele a difference underlying the potential importance of sex difference. Moreover, variants of the ABCB1 gene may explain some portion of the inter-strain differences in opioid-induced hyperalgesia in mice and perhaps other consequences of chronic opioid administration [53].
