Drugs designed to treat depression are increasingly being used to alleviate chronic pain conditions from headaches and back pain to irritable bowel syndrome.

But Australian research has revealed the most commonly prescribed antidepressant offers little or no pain relief, with the study authors urging prescribers to be more aware of the differences in the products.

"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," says the study's author Dr Giovanni Ferreira from The Institute for Musculoskeletal Health and Sydney Musculoskeletal Health at the University of Sydney.

"We showed that is not the case."

In recent years, the prescription of antidepressants to treat chronic pain has increased in popularity.

Only one antidepressant - duloxetine - is approved for treating pain in Australia, specifically nerve pain caused by diabetes.

But "off-label" use is thought to be responsible for a doubling in the number of antidepressants prescribed in OECD countries between 2000 and 2015.

Antidepressants are thought to help with pain by acting on chemicals in the brain that can assist with pain relief, such as serotonin.

Traditional pain relief has been shown to have little to no benefit to those suffering chronic pain. In fact, the UK's National Institute for Health and Care Excellence (NICE) recommends against using any pain medicines to treat chronic pain - only antidepressants.

But not all antidepressants are effective and establishing which ones do the job is vital, the University of Sydney researchers found.

The study, published in The BMJ, reviewed the safety and effectiveness of antidepressants in the treatment of chronic pain - a condition that affects one in five Australians.

The review collated evidence from 26 systematic reviews from 2012 to 2022, involving more than 25,000 participants and including data from eight antidepressants medicines and 22 pain conditions including back pain, fibromyalgia, headaches, postoperative pain and irritable bowel syndrome.

It found that the class of antidepressant most commonly used to treat pain in clinical practice - known as tricyclic antidepressants - had little evidence of working well, or even working at all for most pain conditions.

However, drugs classed as serotonin-norepinephrine reuptake inhibitors (SNRI) antidepressants were found to be effective for the largest number of pain conditions, such as back pain, knee osteoarthritis, postoperative pain, fibromyalgia, and nerve pain.

"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," co-author Dr Christina Abdel Shaheed from The School of Public Health and Sydney Musculoskeletal Health at the University of Sydney.

Dr Ferreira said medicines should not be relied upon exclusively to treat pain. Pain conditions, exercise, physiotherapy and lifestyle changes may also help, he said.