By Pat Anson, PNN Editor

Antidepressants like duloxetine (Cymbalta) are increasingly being prescribed to treat various types of pain, but a new study shows the medications are largely ineffective for people suffering from chronic back pain or osteoarthritis and may even cause harm.

Many clinical guidelines recommend using antidepressants as pain relievers – even when depression is not involved -- yet evidence supporting that use is uncertain. To address that knowledge gap, researchers at the University of Sydney reviewed data from 33 controlled trials involving more than 5,000 adults who took antidepressants for low back or neck pain, sciatica, or hip or knee osteoarthritis.

Their findings, published in The BMJ, show that for people with back pain the effects of antidepressants were too small to be worthwhile, but for those with osteoarthritis there may be a small beneficial effect.

“The use of antidepressants to treat people with chronic back pain and osteoarthritis is increasing worldwide, but prior to our work, it was not clear whether antidepressants relieved pain or were safe,” said lead author Dr. Giovanni Ferreira, PhD, a postdoctoral research fellow at the Institute for Musculoskeletal Health at the University of Sydney. 

“We conducted a review of all randomised clinical trials evaluating the efficacy of antidepressants for people with back pain or knee osteoarthritis and found that for back pain the antidepressants were either ineffective or provided a very small effect, which was unlikely to be perceived as worthwhile by most patients. For people with osteoarthritis, effects were still small, but could be potentially perceived as worthwhile by some patients” 

Ferreira and his colleagues reviewed six classes of antidepressants: serotonin-noradrenaline reuptake inhibitors (SNRIs); selective serotonin reuptake inhibitors (SSRIs); noradrenaline-dopamine reuptake inhibitors (NDRIs); tricyclic antidepressants; and tetracyclic antidepressants. 

Results showed that SNRIs such as duloxetine reduced back pain after three months, but the benefits were so small they were unlikely to be considered clinically important to most patients. SNRIs had a slightly stronger effect on sciatica and osteoarthritis pain. 

Tricyclic antidepressants were ineffective for back pain, but might reduce pain in people with sciatica, although the evidence for that was weak.  

Industry Funded Studies 

Importantly, about two-thirds of people taking SNRI antidepressants experienced an adverse event such as nausea, fatigue, mood swings and weight gain.

“Many people are being treated with these medications that may not be helping their pain and may be doing them harm,” said Ferreira, adding that doctors need to be upfront with patients about possible side effects.

Researchers say the long-term effects of antidepressants prescribed for chronic pain are not well known and many of the studies that do exist were sponsored by industry, raising the risk of bias. 

“Large, definitive trials free of industry ties are urgently needed to evaluate the efficacy of antidepressants,” Ferreira said. “There needs to be more transparency about how evidence coming from those trials is appraised by guideline panels. A good starting point would be to consider all industry-funded trials to be at high risk of bias, and downgrade the strength of recommendations where industry-sponsored trials represent an important part of the available evidence.”

The Food and Drug Administration recently approved duloxetine as a treatment for fibromyalgia in pediatric patients, largely on the basis of a small trial conducted by Eli Lilly, Cymbalta’s manufacturer. Children enrolled in the study did show a modest improvement in pain, but several of them had serious adverse events, including two attempted suicides, suicidal thoughts, an intentional drug overdose, depression and hallucinations.

In their published findings in the journal Pediatric Rheumatology, Eli Lilly researchers downplayed the adverse events associated with duloxetine, saying they were not drug related or “not significantly different” than those of children on placebo. The two attempted suicides aren’t even mentioned.

A common complaint of patients who take duloxetine is how quickly they become dependent and what happens when they stop taking the drug. Many complain of severe withdrawal symptoms, including electric-like sensations called “brain zaps.”

Duloxetine’s checkered history is well known at the FDA. The agency’s adverse events reporting system has recorded nearly 35,000 cases involving duloxetine since 2007, most of them classified as psychiatric disorders. Over 4,000 of those adverse events resulted in death.