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Millions of people worldwide are prescribed antidepressants for the treatment of chronic pain, which is pain that lasts more than three month.
A new review of previous research, published on Tuesday, found that the majority of antidepressants prescribed to treat chronic pain were being prescribed without enough reliable evidence of their efficacy. The potential harms of antidepressants have also not been thoroughly studied.
According to the available evidence, a Cochrane study conducted over a period of two years found that duloxetine was the only antidepressant effective in reducing short-term pain. Cochrane, an international collaboration that includes researchers from around the world, produces a database of systematic summaries on key health questions.
Duloxetine, sold under the brands Irenka and Cymbalta is a serotonin-norepinephrine-reuptake inhibitor, or SNRI. It also increases levels of dopamine, the neurochemical that makes you feel good.
"This is a worldwide public health concern," said Tamar Pincus. She is a professor at the University of Southampton, UK, and a chronic pain researcher.
"Chronic Pain is a Problem for Millions of People who Are Prescribed Antidepressants Without Sufficient Scientific Proof They Help, Nor an Understanding of the Long-Term Impact on Health."
Evidence of effectiveness of commonly prescribed drugs
The review examined 25 antidepressants and 176 studies that involved 28,664 participants. The studies focused on three types of chronic conditions: fibromyalgia (fibromyalgia), nerve pain, and musculoskeletal.
The studies were all randomized controlled trials, which are considered the gold standard of medical research. 72 of the studies were sponsored by pharmaceutical companies.
According to the study, amitriptyline was the most prescribed antidepressant in the world for chronic pain. The antidepressant, sold in the United States as Elavil and Vanatrip and approved by the US Food and Drug Administration in 1961 to treat depression among adults, is available under these brand names in the United States. It is used to treat chronic pain, such as diabetes neuropathy, and migraines.
The authors concluded that most studies on the effectiveness of amitriptyline were small, and the evidence provided was not reliable.
The FDA-approved Milnacipran for fibromyalgia was also effective in reducing pain. However, scientists weren't as confident with this drug, compared to duloxetine, due to the limited number of studies.
The authors urge anyone taking antidepressants to relieve chronic pain to speak with their doctor prior to stopping their medication because of concerns about the new report.
Pain is not uniform
Ryan Patel, research fellow at King's College London's Wolfson Centre for Age Related Diseases, who studies chronic pain, said that antidepressants may help reduce pain due to the overlap between the bodily systems which regulate mood and the pain.
He said that the most important question to be answered by researchers was not if antidepressant medications were effective in treating pain, but rather 'for whom is antidepressant effective?'
Patel, a non-participant in the review, said that even when the cause of chronic back pain is the exact same, the changes in the nervous system can vary. It is therefore no surprise that the pain will present differently in different people, and that not everyone's body will respond the same way to drugs.
Patel said in a press release that 'this comprehensive analysis shows that clinical trials designed poorly, under the assumption everyone's pain experience is uniform, have limited effectiveness for treating chronic pain'.
Study on Long-Term Use Needs
The review concluded that there were no studies on the long-term effects of duloxetine.
Pincus stated that, despite the fact that we found duloxetine to be effective in relieving pain for our patients, we are still concerned about possible long-term damage due to gaps in existing evidence.
The report stated that future research should focus on any adverse effects associated with using antidepressants to treat chronic pain. It noted that existing data was 'poor'.
It (duloxetine), does look good for short-term pain relief at the moment, but I would like to stress that patients don't get prescribed antidepressants for three, four, or six weeks. They are prescribed them for six months. Pincus stated that it is shocking to find out we have no evidence of duloxetine being used long-term.
Dr. Cathy Stannard is the clinical lead for UK National Institute for Health and Care Excellence's (NICE) guideline for Chronic Pain. She is also a pain specialist for NHS Gloucestershire Integrated Care Board, in the UK. She said it was important that people understand the psychological and social influences on their pain experience and the importance of a relationship between a patient and doctor.
Stannard said that the findings of the study show that compassionate relationships and consistency with clinicians are the basis for successful pain management. Stannard was not involved in the study.
Research shows that people most want a strong and empathic connection with their caregiver. They want to have time to talk about what is important to them, and they want to have easy access to support.