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And the modest pain relief sometimes came at a cost of side effects like nausea, vomiting, constipation and drowsiness.
The researchers said the findings add to evidence that for most people with chronic pain, opioids should be a last resort, if they’re prescribed at all.
“Opioids should not be a first-line therapy for chronic, non-cancer pain,” said lead researcher Jason Busse, of the Institute for Pain Research and Care at McMaster University, in Canada.
Dr. Michael Ashburn, a pain medicine specialist at the University of Pennsylvania, in Philadelphia, agreed.
“This is confirmation of the limited role opioids play in treating chronic, non-cancer pain,” Ashburn said.
Most of the daily news on opioids centers on the national epidemic of abuse and addiction — to prescription opioids and illegal forms like heroin.
But Ashburn stressed that the risks go beyond addiction: Patients can suffer side effects even when they diligently take their medication as directed.
“Opioids really only provide modest longer-term effects,” he said. “And taking them for longer periods significantly increases the risk of harm.”
There are already medical guidelines — from the U.S. Centers for Disease Control and Prevention and other groups — that discourage doctors from prescribing opioids for most cases of chronic pain.
The new findings support those recommendations, Busse said.
Prescription opioids include drugs like Vicodin, OxyContin, codeine and morphine. They are powerful analgesics, Busse noted — and they can ease cancer-related pain or severe short-term pain after surgery or an injury.
“But chronic, non-cancer pain seems to be different,” Busse said.
Across the trials his team analyzed, opioids worked better than placebo pills — but not by much. Overall, Busse said, 12 percent more patients saw a “noticeable” difference in their pain after starting opioids, versus placebo pills.
The benefits were even smaller when it came to patients’ physical functioning and sleep quality.
Chronic pain is complex and has different roots, Busse pointed out. But there was no evidence that opioids work well for any particular form, he said.
Some trials, according to Busse, included people with nerve-generated pain — from conditions like sciatica or diabetes-related nerve damage. Others focused on “nociceptive” pain, a broad category that includes conditions like osteoarthritis or pain after a bone fracture or other injury. Some studies followed people with pain related to central nervous system “sensitization” — like fibromyalgia.
Overall, his team found, opioids were no better than non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen. They were also roughly equal to antidepressants, anti-seizure drugs (which are sometimes used for nerve pain) and synthetic cannabinoids.
Since those alternatives are generally safer than opioids, Busse said, it makes sense to try them first.
But, he stressed, there are also non-drug options — including physical therapy, exercise, acupuncture and cognitive behavioral therapy.
None of those approaches were tested in these trials, but other studies have suggested they can help with chronic pain, Busse said.
In the “real world,” Ashburn said, patients often need a combination of therapies. He added that treatment guidelines “clearly state” that even if opioids are prescribed, they should be used in combination with other treatments.
Ashburn stressed another point: Any opioid prescription should be considered a “trial” — and if the drug does not help, it should be discontinued.
But in practice, Ashburn noted, when an opioid isn’t helping, doctors commonly increase the dose.
“We’ve got to get better at knowing when to stop these drugs,” he said.
A recent study by the CDC found that 50 million U.S. adults reported chronic pain — defined as pain on most days for the past six months. That translates to 20 percent of the adult population.