Anti-Inflammatory Drugs May Increase Risk of Pain Becoming Chronic

By Pat Anson

Aspirin, ibuprofen and other non-steroidal anti-inflammatory drugs (NSAIDs) have long been used to relieve back pain, muscle aches and other types of acute, short-term pain. The medications work by reducing inflammation, and are consider safer than stronger analgesics like opioids.

It turns out NSAIDs may do more harm than good by increasing the risk of acute pain becoming chronic.

In a series of studies on lab animals and humans, a team of researchers at McGill University found the NSAIDs, steroids, and other drugs that block inflammation may inhibit the body’s natural healing process. That can make the pain last longer than it should, according to research findings published in Science Translational Medicine.

“Clinical data showed that the use of anti-inflammatory drugs was associated with increased risk of persistent pain, suggesting that anti-inflammatory treatments might have negative effects on pain duration,” wrote lead author Jeffrey Mogil, PhD, a Professor of Pain Research at McGill University.

Mogill and his colleagues studied the transition from acute to chronic low back pain (LBP) in 98 adults by analyzing their immune cells. They focused on neutrophils, a type of white blood cell that is attracted to sites of inflammation and releases chemicals that promote an immune response to fight infection and heal tissue.

In participants whose lower back pain resolved and did not become chronic, researchers found evidence that their neutrophils and other natural biological processes performed normally, protecting them from transitioning to chronic pain.

Participants whose pain turned chronic showed signs that the healing process and neutrophils were impaired. This suggests that anti-inflammatory drugs that block neutrophils may interfere with the healing process by reducing inflammation too soon.

To test their theory, researchers analyzed health data from 500,000 people in the UK Biobank project, a long-term research study, to see if the medications they took for acute back pain had any negative consequences. They found that people who took NSAIDs had a higher risk of reporting chronic back pain 2 to 6 years later. Those who took antidepressants, which do not interfere with inflammation, did not have a higher risk of chronic pain.   

In animal studies, the McGill researchers found that laboratory mice given anti-inflammatory drugs had pain that lasted up to ten times longer than normal. Interestingly, mice given gabapentin, morphine or lidocaine – analgesics that do not have anti-inflammatory properties – did not experience longer pain episodes.

None of this proves anything – correlation is not causation – but it suggests that anti-inflammatory drugs may not be good for long-term pain management. They may be effective for short-term pain relief, but have the unintended effect of making pain last longer. If confirmed in future studies, researchers say their findings could have a substantial impact in how we manage pain.

“Together, our results suggest that active immune processes confer adaptation at the acute pain stage, and impairment of such inflammatory responses in subjects with acute LBP increases the risk of developing chronic pain,” researchers said. “Specifically, our data suggest that the long-term effects of anti-inflammatory drugs should be further investigated in the treatment of acute LBP and likely other pain conditions.”