Why pain “hurts” some people more — and what to do about it

J Mogil

Dr. Jeffrey Mogil and his colleagues are studying why people respond differently to pain.

Why do some people feel pain more than others? Why do painkillers help some people but not others? Answering these complex questions is the research focus of Dr. Jeffrey Mogil, McGill Psychology Professor and E. P. Taylor Chair in Pain Studies.

“We’re interested in the question of individual differences in pain,” says Dr. Mogil. “We know, for example, that if 100 people have the same operation, some of them will develop chronic pain while most will heal up just fine. In the same way, a dose of morphine will work spectacularly well in some people and not at all in others. To understand why this is, we first study pain responses in mice then try to find out if our results also apply to humans.”

Genes, environmental factors, stress and social factors all play a role in the different responses to pain. So does sex, but not in the way many people would expect. While women are slightly more sensitive to pain than men on average, there is increasing evidence that the way the brain processes pain differs dramatically between the genders.

Differences in pain response could have significant implications

Dr. Mogil and his colleagues recently received a grant from Brain Canada to fund a multi-centre study of the different mechanisms of pain processing in males and females. The differences are dramatic, and could have significant implications for how pain is treated.

Acute pain in a neck at the young women

Females process pain differently than males, a finding which may one day lead to “his” and “her” analgesics.

“In mice, the response to pain involves different genes and chemicals in males and females,” Dr. Mogil says. “Even more interesting, it appears to involve completely different types of cells. The fundamental cellular and molecular signaling pathways for chronic pain in female mice are different from those in male mice. There are bigger sex differences than we realize. We may be looking at ‘the tip of an iceberg.’”

While hundreds of studies have been published about pain responses in male mice and rats, there is very little in the literature about responses in females. Dr. Mogil and his colleagues are trying to learn how the female pain response system works, define the generalizability of sex differences and learn whether these exist in other animals.

Preclinical research all done in male subjects

“The research of the past few decades hasn’t resulted in many innovations in pain treatment,” Dr. Mogil says. “We think we have identified one reason for this — preclinical research is all done in male rats and mice but then the clinical trials are being done in men and women – and they are failing. It used to be thought that results from male mice were more reliable because they didn’t cycle, but this has now been disproved.”

Mogil quoteAnother reason for the relative lack of progress in pain research may simply be the incredible complexity of the human brain. “We’re trying to understand the most complicated thing we know of ,” Dr. Mogil notes. “How can you explain a brain if you only have a brain to do it with?”

While research into sex-specific responses to pain is still in its early stages, one possible result may be the development of different pain medications for men and women. “It’s conceivable that we may develop analgesics which work for one sex but not the other,” says Dr. Mogil. “In effect, we may end up with ‘pink pills’ and ‘blue pills’ in our medicine cabinets.”

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