Antidepressants are often used for pain relief, but new research shows they might not be as effective as first thought - or even the best option.
Consumption of antidepressants has more than doubled in OECD countries over the past 20 years, and the often off-label use of these medicines to treat chronic pain conditions is believed to be contributing to the increase.
Many people are dealing with ongoing pain – about one in five globally – and yet drug options for treatment are limited and the potential harm of many medications may outweigh the benefits. Opioids are highly addictive, for instance, and long-term use of anti-inflammatories can have numerous adverse effects, including kidney and gastrointestinal risks.
In its most recent guidelines for managing primary chronic pain (defined, in this case, as pain with no clear underlying cause, or pain or its impact that is out of proportion to any observable injury or disease), the UK’s National Institute for Health and Care Excellence (Nice) recommended against using any pain medicine, with the exception of antidepressants.
The guidelines sparked curiosity in researchers at the University of Sydney’s Institute for Musculoskeletal Health. After all, a lot of diverse health problems are grouped together and defined as chronic pain conditions, from fibromyalgia to irritable bowel syndrome. And the term antidepressants is used to describe a range of very different drugs.
Led by Dr Giovanni Ferreira, the researchers reviewed all the existing evidence about the effectiveness of antidepressants to treat chronic pain, delving into data covering 22 pain conditions and eight different classes of the drug.
Ferreira says, “What we’ve shown is that some antidepressants may be effective for some pain conditions but not for others. You can’t just lump everything into one broad term.”
Tricyclic antidepressants such as amitriptyline are commonly used for pain, but this latest review found that for most conditions they were ineffective or the evidence for their efficacy was inconclusive.
“They did seem to reduce pain for people with irritable bowel syndrome, nerve pain and chronic tension-type headaches,” says Ferreira.
A class of drugs known as SNRIs (serotonin and norepinephrine reuptake inhibitors) was effective for a larger number of pain conditions including back pain, post-operative pain, fibromyalgia and nerve pain.
Meanwhile, SSRIs (selective serotonin reuptake inhibitors), which are usually the preferred medication for moderate to severe depression, proved not to be as helpful for pain.
The researchers found there was an absence of high-certainty evidence and that many of the clinical trials that have been done had ties to the pharmaceutical industry.
How antidepressants help relieve pain is not very well understood, although it seems likely they affect chemicals in the brain involved with pain perception. We do know they can have a range of unpleasant and potentially dangerous side effects, particularly when taken by elderly people.
And so there is an increasing focus on drug-free strategies for pain, such as physical activity, weight reduction, physiotherapy and psychological therapies.
Ferreira believes there is a place for both approaches. “There’s a lot of trial and error involved in the management of chronic pain and people need to think about what works for them, but medicines do have a role and I think we need to remove the stigma around using them. Some people rely on pain medication so they can function. And the ultimate goal is to improve quality of life.”
There can also be some stigma associated with taking antidepressants. “Both patients and clinicians can be reluctant to use them,” says Ferreira. “For patients, sometimes there is the idea that the doctor is suggesting the pain is all in their head.”
In the Netherlands, prescription of amitriptyline for people with osteoarthritis has increased by 17% in the past decade. Among older people, data from Canada, the US, the UK and Taiwan suggests chronic pain is the most common condition leading to an antidepressant prescription – even more so than depression.
Ferreira believes this new review clearly shows a more nuanced and individualised approach is needed when prescribing these drugs to treat pain.
He says, “Clinicians and patients shouldn’t be misled into thinking that all antidepressants have the same effectiveness for pain conditions. We have shown that is not the case.”
