Do Prescription Opioids Prolong Pain?

By Beth Leipholtz 04/24/18
For a new study, researchers set out to examine the effect of using morphine to ease post-surgery pain.
Image: 
woman grabbing her shoulder in pain

The purpose of most prescription opioids is to help with pain, particularly in situations like post-surgery. 

But a recent study is questioning just how effective opioids actually are in such circumstances. The study was conducted by researchers at the University of Colorado Boulder and found that rather than taking away pain, opioids may actually prolong it. 

In the study, lead author Linda Watkins of the Department of Psychology and Neuroscience and her colleague Peter Grace of MD Anderson Cancer Center in Houston, Texas, conducted a procedure called a laparotomy on male rats, according to Medical News Today.

The procedure consists of cutting through the abdominal wall to get to the inside of the abdomen, and it’s done thousands of times each year in the U.S. 

After the procedure, one group of the rats were given a “moderate dose” of morphine for seven days. Another group was given morphine for eight days. The dosage was tapered off by the 10th day, according to Medical News Today.

Yet another group of rats was given morphine for seven days, ending one week before the procedure.

Both before and after the morphine was given, researchers measured the rats' “sensitivity to touch” and “activity of genes related to inflammation in the spinal cord.” 

The results showed that in comparison to rats that were given saline, the ones who had morphine struggled with post-surgery pain for three weeks longer. Additionally, researchers found that the longer morphine was given to the rats, the longer their pain carried on. Tapering was also found to make no difference at all in pain. 

"This tells us that this is not a phenomenon related to opioid withdrawal, which we know can cause pain,” Grace stated, according to Medical News Today. “Something else is going on here."

Watkins says this has to do with a “one-two hit” on glial cells. 

“In the brain, glial cells are more numerous than neurons,” Medical News Today states. “They protect and support nerve cells and, as part of their role as protector, they direct the brain's immune response, including inflammation.”

With glial cells, the first hit happens when surgery “activates glial cells' toll-like receptor 4 (TLR4).”

According to Watkins, these receptors help manage “inflammatory response.” Then comes the second hit, in the form of morphine. 

"With that second hit, the primed glial cells respond faster, stronger, and longer than before, creating a much more enduring state of inflammation and sometimes local tissue damage,” Watkins said. 

For the rats that were given morphine that ended a week before surgery, there was no prolonged pain after surgery, which led researchers to believe there is “a critical window for morphine potentiation of pain,” Medical News Today states.

This study has only been conducted on animals and will need to be tested on humans before any more headway is made. 

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Beth is a Minnesota girl who got sober at age 20. By day she is a website designer, and in her spare time she enjoys writing about recovery at www.lifetobecontinued.com, doing graphic design and spending time with her boyfriend and three dogs. Find Beth on LinkedInInstagram and Twitter.

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