A new study that finds opioid use increases chronic pain in rats may have important implications for humans, according to researchers from the University of Colorado-Boulder.

The researchers found that rats who received morphine for five days experienced chronic pain that continued for several months, by triggering the release of pain signals from spinal cord immune cells called glial cells.

The findings may help explain the recent surge in prescription painkiller addiction, Forbes reports.

“We are showing for the first time that even a brief exposure to opioids can have long-term negative effects on pain,” study author Peter Grace said in a news release. “We found the treatment was contributing to the problem.”

Study co-author Linda Watkins added, “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. This is a very ugly side to opioids that had not been recognized before.”

The findings will be published in the Proceedings of the National Academy of Sciences.