Fibromyalgia patients often suffer from chronic pain, but for some reason they find commonly prescribed pain medications are not very effective. Researchers at the University of Michigan Health System believe they may know the reason.

Pain killers, like Darvocet,Vicodin, and Oxycontin, work by binding to opioid receptors in the brain and spinal cord. The study of 17 women with fibromyalgia and a control group of 17 women without the condition underwent positron emission tomography (PET) scans. What researchers found is the fibromyalgia patients had reduced mu-opioid receptors (MOR) in the regions of the brain that normally process and dampen pain signals.

Researchers also found a possible link with depression. The PET scans showed that fibromyalgia patients, with depressive symptoms, had reductions of MOR bindings in a region of the brain thought to modulate mood and the emotional dimension of pain.

The researchers findings are significant because it has been difficult to determine the reason for chronic pain in fibromyalgia patients, which is one of the reason physicians have been slow to accept the diagnosis of fibromyalgia as a ‘real’ disease.