How do long-term opioids affect chronic back pain and brain activity?

Chronic back pain patients who have used prescription opioids for an average of 7.8 years report pain levels nearly identical to those who avoid the drugs entirely, according to new research from Northwestern University. The study compared 70 long-term opioid users with 70 matched non-users, finding no improvement in pain or functioning among the medicated group.

Brain Activity and Molecular Markers Identified

While physical outcomes showed little difference, researchers observed large disparities in brain activity between the two groups. The team identified new molecular markers, including some involving serotonin receptors, which could pave the way for novel treatments for pain management and opioid tapering. Based on these findings, scientists plan to test whether an antidepressant targeting the same serotonin pathway can help treat chronic pain and dependence.

The study, published on Oct. 1 in the journal Brain, highlights a nuanced reality: although the opioid group did not fare better, they were not significantly worse off either. "The psychological and brain properties of the participants on long-term prescription opiates were essentially intact," said senior author A. Vania Apkarian, director of the Center for Translational Pain Research at Northwestern University Feinberg School of Medicine.

Preserved Brain Anatomy Despite Usage

Apkarian noted that this finding counters widespread fears about immediate neurological damage from opiate ingestion. "That's good news because there's this fear nowadays that as soon as you start ingesting opiates, your brain is going to go crazy, and it doesn't," Apkarian said. "But the bad news is that we saw no sign that their pain had gotten any better by using this drug for so many years."

Roughly 5 million U.S. adults regularly use prescription opioids to manage chronic pain. Apkarian emphasized that study participants took low or moderate doses under medical supervision. This research marks the first time long-term opioid consumption has been examined alongside brain properties in such detail.

Striking Differences in Neural Networks

Pain levels reported by both groups were nearly identical, averaging about 5.4 on a 10-point scale. However, the opioid group exhibited slightly worse results regarding physical function and mental health. Beyond subjective reports, scientists used functional MRI to examine brain anatomy and activity. Reassuringly, the team found little evidence that years of opioid use altered the brain's structure.

Significant differences emerged in spontaneous brain activity, particularly within the mesocorticolimbic network, which governs reward and motivation, and the prefrontal cortex, responsible for decision-making. To analyze these variations, Apkarian and colleagues developed a computational technique merging MRI data with published maps of neurotransmitter receptors.

New Pathways for Treatment Development

This method revealed molecular signatures linked to different aspects of chronic pain and long-term opioid use, specifically involving serotonin and opioid brain receptors. "For me, that's the most exciting part of the study," Apkarian said. "We identified molecular markers of different states of that brain in chronic pain patients. And this gives us clues for what kind of new treatments to pursue, what kind of drugs to try and what kind of drugs not to use."

The research also included 21 patients who completed a four-week pain rehabilitation program. Eight of these individuals finished the course, providing additional data points on recovery trajectories relative to long-term medication use.