New York – Researchers have published a study in the Journal of Neuroscience that claims to explain why pain relievers are often found to be less effective in women.

The study found that when microglia, the brain’s resident immune cells, were blocked, female response to opioid pain medication improved and matched the levels of pain relief normally seen in males. The finding that microglia are more active in brain regions involved in pain processing may contribute to why the incidence rates for various chronic pain syndromes are significantly higher in females than males.

Morphine is one of the most commonly used drugs for the treatment of severe or chronic pain, however it is often less effective in females. Studies have indicated that females require almost twice as much morphine as males to produce comparable pain relief and the latest study examined a potential explanation for this phenomenon – the sex differences in brain microglia.

In healthy individuals, microglia survey the brain, looking for signs of infection or pathogens. In the absence of pain, morphine interferes with normal body function and is viewed as a pathogen, activating the brain’s innate immune cells and causing the release of inflammatory chemicals such as cytokines.

To test how this sex difference affects morphine analgesia, Doyle gave male and female rats a drug that inhibits microglia activation.

Findings of the study have important implications for the treatment of pain, and suggests that microglia may be an important drug target to improve opioid pain relief in women.