The Long-Term Side-Effects Of Painkillers Are Startling

Long-term effects of short-term pain relief could be startling.

Long-term effects of short-term pain relief could be startling.

Painkilling opioids like morphine could actually prolong pain rather than reduce it, according to research on mice.

Scientists found that just a few days of treatment with an opioid led to chronic pain that went on for months.

In the long-term, the opioid increased the pain signals sent from immune cells in the spinal cord.

Some of the most common opioids are:

  • codeine,
  • meperidine (Demerol),
  • hydrocodone (Hysingla ER, Zohydro ER),
  • fentanyl (Actiq, Duragesic, Fentora),
  • hydrocodone/acetaminophen (Lorcet, Lortab, Norco, Vicodin),
  • hydromorphone (Dilaudid, Exalgo),
  • and methadone (Dolophine, Methadose).

Professor Peter Grace, who led the study, said:

“We are showing for the first time that even a brief exposure to opioids can have long-term negative effects on pain.

We found the treatment was contributing to the problem.”

The study on mice treated an injury with opioids.

The scientists found that the long-term consequences of taking the drugs were serious.

The injury plus the opioid delivered a kind of ‘one-two punch’ to cells in the spinal cord called microglia.

Professor Linda Watkins, one of the study’s authors, said:

“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.”

Around 100,000 people in the US died of prescriptions opioid overdoses in 2020-2021 (Dyer, 2021).

Increased pain is not the only risk from opioids, they are also addictive.

People given opioid pain medication are 25 percent more likely to use the drugs chronically, a recent study found.

Study author Dr Susan Calcaterra said:

“These drugs are highly effective for pain control, but also cause feelings of euphoria.

For these reasons, patients may ask their physicians for additional opioid medication even after their acute issue is resolved.”

Dr Calcaterra continued:

“…patients [given opioid painkillers] were more likely to become chronic opioid users and had an increased number of opioid refills one year post-discharge, compared to patients without opioid receipt.

They were five times more likely to be chronic users after one year.”

The studies were published in the journals PNAS and the Journal of General Internal Medicine (Grace et al., 2016Calcaterra et al., 2015).


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This site is all about scientific research into how the mind works.

It’s mostly written by psychologist and author, Dr Jeremy Dean.

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Author: Jeremy Dean

Psychologist, Jeremy Dean, PhD is the founder and author of PsyBlog. He holds a doctorate in psychology from University College London and two other advanced degrees in psychology. He has been writing about scientific research on PsyBlog since 2004. He is also the author of the book "Making Habits, Breaking Habits" (Da Capo, 2013) and several ebooks.