News from a research team studying the effects of opioids may help explain the explosion in prescription painkiller addictions of the last several years. A University of Colorado-Boulder study has found that opioid use increases chronic pain in rats. If the same result holds true in humans, it would mean that prescribed opioids aren’t only viciously addictive, they also worsen the very condition they’re prescribed to treat.
The study showed that just five days of morphine treatment in rats caused chronic pain that continued for several months by triggering the release of pain signals from immune cells in the spinal cord.
“We are showing for the first time that even a brief exposure to opioids can have long-term negative effects on pain,” said CU-Boulder assistant research professor Peter Grace, a faculty member in the Department of Psychology and Neuroscience. “We found the treatment was contributing to the problem.”
The immune cells in the spinal cord, known as glial cells, normally play the role of clearing out infection-causing microorganisms. When the body is in pain, signals are sent that place glial cells on high alert. In rats, what appears to happen after a few days of morphine treatment is the opioids send repeated signals to the glial cells, causing a “glial cascade.” In turn this cascade produces a cell signal from a protein called interleukin-1beta (IL-1b), which increases the activity of nerve cells in the spinal cord and brain, resulting in intensified chronic pain that lasts several months.
“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 of CU-Boulder. “This is a very ugly side to opioids that had not been recognized before.”
Again, the study hasn’t yet been conducted in humans, so for the time being the results are cautionary. But this isn’t the first study investigating the issue, with previous researching suggesting that opioids lengthen chronic pain after major surgery.
If the latest findings hold true, they’d help explain the vicious cycle of prescription opioid use. The drugs numb pain at the surface level, but below the surface they may be drawing out how long a patient experiences pain, thereby extending how long the drugs are taken. Since opioid addiction can begin after a relatively short period of time, it’s easy to see how this effect could be contributing to the epidemic of painkiller addictions that’s been building for the last 15 years. The next phase of this research will be worth keeping an eye on.
The study was published in the Proceedings of the National Academy of Sciences.