Relative to men, women present with pain conditions more commonly. Although consistent differences exist between men and women in terms of physiological pain sensitivity, the underlying mechanisms are incompletely understood and yet could inform the development of effective sex specific treatments for pain. The gut microbiota can modulate nervous system functioning, including pain signaling pathways. We hypothesized that the gut microbiota and critical components of the gut-brain axis might influence electrical pain thresholds. Further, we hypothesized that sex, menstrual cycle, and hormonal contraceptive use might account for inter-sex differences in pain perception.