Figure 4.

Pentazocine analgesia by sex and MC1R genotype (two variant alleles vs. zero or one variant alleles) in humans. Bars represent mean (± SEM) difference scores for summed pain intensity ratings during each pain procedure (thermal pain, a; ischemic pain, b) were computed by subtracting postdrug from predrug ratings. No differences were observed in baseline pain responses or pain responses to saline administration across sex or genotype. *, Significantly different from other genotype within sex, P < 0.05.