Researchers at the University of Colorado-Boulder have discovered yet another disadvantage of narcotic painkillers.

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While the introduction of the dangers of abuse and addiction come as no surprise to most, a three-month study conducted by the university displayed an increase in chronic pain in lab rats by the use of opioids such as morphine, an effect known as hyperalgesia.

“Our key finding is that we were able to demonstrate that a brief treatment with a pain killer, like morphine, doubled the duration of chronic pain,” said Peter Grace, an Assistant Reasearch Professor in the department of psychology and neuroscience.

Researchers mimicked chronic nerve pain found in humans that would send messages from the nerve cells to the spinal cord, putting glial cells in what they call “alert mode.” They then treated the pain with morphine.


Researchers say that, in rats, the opioids send repeated signals to these glial cells, causing a “glial cascade” with causes the production of a signal from the cell protein interleukin-1beta (IL-1b). The production of IL-1b increases the activity of nerve cells in the spinal cord and brain, resulting in a stronger pain that continued for several months.

According to Peter Grace, the findings suggest that increasing opioid prescriptions for humans could have similar effects, intensifying chronic pain.

“The implications for people taking opioids like morphine, oxycodone and methadone are great, since we show the short-term decision to take such opioids can have devastating consequences of making pain worse and longer lasting,” said Professor Linda Watkins, who also led the study. “This is a very ugly side to opioids that had not been recognized before.”

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