It's true, says Mogil, that women are more likely than men to seek medical attention for pain, to report it as worse, and to be less self-consciously stoic. But, he says, "you get the same differences in animals"—female mice seem to have a somewhat lower pain threshold than their male counterparts. Plus, he adds, research on human newborns shows that girls grimace more in response to a heel lance (a poke with a sharp tool) than male babies do. "I'm certainly not saying that there are no sociocultural explanations for these sex differences. All I'm saying is that males and females seem to be set up differently from the start, in their pure, core biology."
After some initial resistance, the scientific community has come around to Mogil's way of thinking. It has recently been shown that estrogen influences pain sensitivity; male experimental animals injected with the hormone seem to have a lower pain threshold than before, whereas an injection of testosterone seems to raise the threshold in female animals. In fact, estrogen may act as a switch, turning on the ability to recognize pain.
Given such groundbreaking discoveries, you'd think doctors would happily prescribe the most powerful painkillers to women—but they don't. Women were twice as likely as men to be undertreated for pain, in a study of 550 AIDS patients at Memorial Sloan Kettering Cancer Center and other major facilities in New York City. In all fairness, doctors do worry about side effects and dependency, so they're reluctant to give women strong but potentially addictive drugs like opioids (morphine, OxyContin), especially because the government has been cracking down on physicians who overprescribe them. And even though scans can display the brain's response to pain—sometimes in living color—the sensory experience remains subjective. At this point, having a patient rate her pain on a scale of one to ten is the most reliable tool a doctor has to knowing how she feels physically: "The only real way to get at how much pain a person is in," Mogil says, "is to ask them, and trust them." Still, in his opinion, "the danger of not believing people is much greater than the danger of overprescribing opioids. The big challenge we have is educating medical doctors. Politicians are even harder, but medical doctors are also thick as bricks."
An especially thorny problem for researchers like Mogil is the relief of chronic pain, which the medical profession long dismissed as the collateral damage of disease. "Chronic neuropathic pain [the kind that results from nerve damage from an injury, for example] can last five years, ten years, for the rest of your life," Mogil says. "It's really horrible for a lot of people." The good news is that chronic pain has finally come to be considered a disease in its own right. "People used to think, 'Get rid of the disease and you'll get rid of the pain,'" Mogil says. But that approach was utterly wrongheaded. "Pain is there to enable us to learn our physical limitations—to keep us from walking on a broken leg, or to teach a toddler not to keep jumping off a bunk bed. What's the reason to have pain in your arm five years after that gunshot wound? There's no injury anymore, right? Chronic pain has no use, and things that have no use and yet cause difficulties are diseases."