Long-term opioid use can prolong chronic pain for injured workers, according to members of the medical industry, but there is new concern that use of the narcotic for only a few days can increase chronic pain episodes.

Patients who have been receiving opioids for long periods sometimes begin to see their pain threshold moving in the wrong direction, observers say.

“Chronic opioid therapy can sensitize the brain and the nervous system to pain, having an effect on a patient where they have increased pain or worsening pain from the opioids,” said Dr. Robert Hall, Westerville, Ohio-based medical director for the workers comp division of medical cost management firm Optum Inc.

The prescriber often increases the dose because of the worsening pain, Dr. Hall said.

“It’s a spiral that is causing trouble for injured workers because the opioid dosage keeps going up without the condition being recognized, that the sensation of pain becoming worse is from the painkillers,” he said.

New findings also show that an increase in chronic pain caused by opioids may also occur with prescriptions over short periods of time.

A recent study led by research professors at the University of Colorado Boulder, found that when lab rats were given opioids for just a few days, it caused an increase in chronic pain that went on for several months.

Peter Grace, an assistant research professor who led the study with Linda Watkins, both faculty members in CU-Boulder’s Department of Psychology and Neuroscience, said May 31 in a press release announcing study results that they are “showing for the first time that even a brief exposure to opioids can have long-term negative effects on pain,” finding that “the treatment was contributing to the problem.”

In the study released in May, results showed opioids having a cascade effect on the rats. In people, opioids can have multiple effects on different parts of the body and that can worsen pain, Dr. Hall said.

“We are learning that every part of the body has opioid sensors and responds in different ways when (opioids) are being used,” Dr. Hall said.

It’s a study on animals, however, this study is a “step forward” in saying that there probably is a physiological mechanism here, said Dr. Kathryn Mueller, medical director for the Colorado Division of Workers’ Compensation, president of the American College of Occupational and Environmental Medicine, and a professor at the University of Colorado Denver’s Anschutz Medical Campus.

“It’s an important study that further supports the idea that opioids do have a physiological effect when there was some debate about it before,” she said, adding that there has been a lot of controversy in the medical industry where some don’t believe this happens, but the majority of providers think it does occur over time.

Replicating these results in humans could prove that it’s not just using opioids over a long period of time that causes issues, if it can be proven that this reaction occurs in a short period of time it could change the response to this issue, Dr. Mueller said.