Antidepressants used for chronic pain on the rise, but are they effective?

Many people are unaware that some antidepressants (medications used to treat people living with depression) are also being prescribed to treat certain chronic pain conditions.

Chronic pain affects between one-third and one-half of the UK population. The treatment of chronic pain is often suboptimal, with commonly used medicines having limited or unknown benefits, and sometimes harmful side effects. Antidepressants are prescribed to help manage chronic pain, even when the person affected does not have a mood disorder like depression. Their use has been increasing over time.

An international team of researchers, including academics from the University of Warwick, has found that some classes of antidepressants were effective in treating certain pain conditions in adults, but others were either not effective, or the effectiveness was unknown.

Published in The BMJ, the study reviewed the safety and effectiveness of antidepressants in the treatment of chronic pain, and for the first time, brings together all the existing evidence in one document.

The researchers say the results show that clinicians need to consider all the evidence before deciding to prescribe antidepressants for chronic pain management.

Professor Martin Underwood from the University of Warwick, a co-author of the paper, said:

"There is a role for antidepressants in helping people living with chronic pain, however, this is more limited than previously thought.

Antidepressants may have unpleasant side effects that patients may wish to avoid.

We need to work harder to help people manage their pain and live better, without relying on the prescription pad."

The review examined 26 systematic reviews from 2012 to 2022 involving over 25,000 participants. This included data from eight antidepressant classes and 22 pain conditions including back pain, fibromyalgia, headaches, postoperative pain, and irritable bowel syndrome. Serotonin-norepinephrine reuptake inhibitors (SNRI) antidepressants such as duloxetine were found to be effective for the largest number of pain conditions, such as back pain, knee osteoarthritis, postoperative pain, fibromyalgia, and neuropathic pain (nerve pain).

By contrast, tricyclic antidepressants, such as amitriptyline, are the most commonly used antidepressant to treat pain in clinical practice, but the review showed that it is unclear how well they work, or whether they work at all for most pain conditions.

The use of antidepressants as a treatment for pain has recently gained attention globally. A 2021 guideline for chronic primary pain management published by The National Institute for Health and Care Excellence (NICE) recommends against using pain medicines with the exception of antidepressants. The guideline recommends different types of antidepressants, such as amitriptyline, citalopram, duloxetine, fluoxetine, paroxetine or sertraline for adults living with chronic primary pain.

Lead author Dr Giovanni Ferreira from The Institute for Musculoskeletal Health and Sydney Musculoskeletal Health at the University of Sydney said a more nuanced approach to prescribing antidepressants for pain is needed.

"Recommending a list of antidepressants without careful consideration of the evidence for each of those antidepressants for different pain conditions may mislead clinicians and patients into thinking that all antidepressants have the same effectiveness for pain conditions. We showed that is not the case."

Co-author Dr Christina Abdel Shaheed from The School of Public Health and Sydney Musculoskeletal Health at the University of Sydney said:

"The findings from this review will support both clinicians and patients to weigh up the benefits and harms of antidepressants for various pain conditions so that they can make informed decisions about whether and when to use them."

Dr Ferreira said that there are multiple treatment options for pain, and people should not rely solely on pain medicines for pain relief.

"Some pain medicines may have a role in pain management, but they need to be considered as only part of the solution. For some pain conditions, exercise, physiotherapy, and lifestyle changes may also help. Speak to your health professional to learn more about what alternatives might be appropriate for you,"

This review distilled the evidence from over 150 clinical trials into an accessible summary that clinicians can use to help them make better decisions for their patients with chronic pain.

The current status of antidepressants globally

Most antidepressant prescriptions for pain are 'off-label', meaning that these antidepressants have not been approved to be prescribed for pain. Many antidepressants are thought to help with pain by acting on chemicals in the brain that can assist with pain relief, such as serotonin. However, it is unknown exactly why some antidepressants improve pain.

The use of antidepressants has doubled in OECD countries from 2000 to 2015, and the use of 'off-label' prescriptions of antidepressants for pain is considered a contributing factor to this increase. Data from Canada, the United States, the United Kingdom and Taiwan, suggest that among older people, chronic pain was the most common condition leading to an antidepressant prescription, even more so than depression.