The study showed that use of opioid increases chronic pain in rats. The researchers claim that only five days of morphine treatment in rats caused chronic pain and the pain remained for several months.
"We are showing for the first time that even a brief exposure to opioids can have long-term negative effects on pain," said UC-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, also known as glial cells, are responsible for clearing out infection-causing microorganisms. When the body is in pain, signals are sent placing glial cells on high alert. The study showed that in rats after a few days of morphine treatment the opioids send repeated signals to the glial cells, causing a "glial cascade."
"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 UC-Boulder. "This is a very ugly side to opioids that had not been recognized before."