Results from a new study may explain why female patients often require higher doses of morphine – one of the primary drugs for the treatment of chronic or severe pain – than male patients to achieve the same level of relief. It appears that a type of immune cell called microglia are more active in the pain-processing regions of the female brain.

Share on Pinterest The researchers say that their study shows a need for different strategies for managing chronic pain in men and women.

Writing about their findings in the Journal of Neuroscience, researchers from Georgia State University in Atlanta explain how after blocking microglia in rats, they found the response to opioid pain-relieving drugs in females matched that of males.

Chronic pain is the most common human health problem – it is thought to affect more than 1 in 4 people worldwide, with higher incidence occurring in older populations.

It is well-established that chronic pain affects more women than men. One might reasonably conclude that this is because a number of chronic pain illnesses, such as endometriosis and menstrual pain, can only occur in women.

However, even pain conditions that occur in both sexes – from headaches, migraine, and osteoarthritis knee pain, to fibromyalgia and chronic fatigue syndrome – overwhelmingly affect women more than men.

Yet even though it is clear that such differences exist, it is proving rather difficult to discover whether they are due to actual “sex differences” in pain sensitivity.

For their investigation, senior author Anne Murphy – an associate professor who heads a pain research group in the Neuroscience Institute at Georgia State – and colleagues chose to study morphine, the primary drug for relieving severe or chronic pain.