Pain inhibition, nicotine, and gender.

The ability of nicotine to decrease sensitivity to pain in humans has been a subject of dispute. Decreased sensitivity has been demonstrated in studies involving men, whereas the effect has been less obvious or absent in studies involving predominantly, or entirely, women. To determine whether there are gender differences in nicotine's hypoalgesic actions, ratings of electrocutaneous stimulation were obtained from 30 male and 44 female smokers and nonsmokers under placebo and nicotine conditions. Nicotine increased the pain threshold and tolerance ratings of men but had no effect on the pain ratings of women. Among men, there was no effect of smoking history, suggesting that the changes in pain perception reflect a direct pain-inhibitory effect of nicotine rather than a relief from acute nicotine withdrawal. Nicotine had no effect on mood or task ratings, indicating that the antinociceptive effects observed were not due to nicotine's putative mood effects.