In the long run, morphine might actually cause more pain than it alleviates

Painkillers in the opium family (most notably morphine) may actually make pain last longer, a new study reports. Morphine treatment after a nerve injury doubled the duration of pain in rats and this is highly worrying.

Morphine treatment extended the duration of nerve pain in rats, a result that raises questions about the effects of other opioid-based painkillers, such as OxyContin.

It gets even more disturbing when you consider the addictive potential of many commercial opioids such as OxyContin and Vicodin. If this is true, then people are becoming addicted to something that’s extending their pain even longer, suggesting that “the treatment is actually contributing to the problem,” says study coauthor Peter Grace, a neuroscientist at the University of Colorado Boulder.

It’s not the first time opioids have been discussed in this context. Doctors have known for a while that for some people, opioids enhance the pain sensitivity, a condition called opioid-induced hyperalgesia. In this new study, the negative effects lingered for a few weeks even after the treatment was stopped. These experiments were done with male rats, but unpublished data indicate that morphine extends pain even longer in female rats, Grace says. Previous studies suggest there wouldn’t be any major difference between male and female results.

However, this is still just a rat study, and we don’t know if the same effects would be exhibited in humans, nor is it known if all opioids behave similarly. Clarity on how opioids influence pain could change doctors’ prescribing habits and promote better treatments, but the study has to be replicated in humans before we can draw any definite conclusions.

Journal reference: P. M. Grace et al. Morphine paradoxically prolongs neuropathic pain in rats by amplifying spinal NLRP3 inflammasome activation.Proceedings of the National Academy of Sciences. Published online the week of May 30, 2016. doi: 10.1073/pnas.1602070113.

4 thoughts on “In the long run, morphine might actually cause more pain than it alleviates

  1. pa07950

    This story has been picked up too many times to count and only a few sites put this test into context. First – this was a test on rats, not humans. Humans also have an emotional side of pain that is not taken into account. Second – the morphine was injected directly into the spine. The dosing of morphine and its quick cessation likely caused repeated withdrawal that can increase stress and inflammation. Humans in the hospital usually don’t experience the same withdrawal because they take sustained-release formulations and taper off opioids gradually.

    What this study may point out is the following: when pain is treated and it's not given in regular cycles allowing the patients to go back into severe pain, they end up taking longer to heal.

    Finally I should note: chronic pain is defined as pain that lasts more than 6 months. The induced pain here was for 10 days and the total study was 3 months so any results cannot be applied to chronic pain (not mentioned in your article, but was by others).

  2. John

    Your comment does point out a few limitations, but not all are accurate. Morphine was injected systemically, and not directly into the spine. The idea that the pain is caused by repeated withdrawal is put to rest by control groups that had no pain, but still received morphine. These rats did not develop persistent pain. A final note on rat vs human comparisons: your definition of chronic pain pertains to humans, and can't easily be translated to rats with a lifespan of ~2 years.

  3. Brian

    I'll wait for it to be replicated, but all it means is that people need to take the morphine for twice as long as they would have had to endure intense pain. Seems fine to me.

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