Non-steroidal anti-inflammatory drugs (NSAIDs) alone offered as much relief as more powerful painkillers.
This was surprising, said lead author Dr. Benjamin W. Friedman of Montefiore Medical Center at Albert Einstein College of Medicine in the Bronx, New York.
"I think it was generally believed that opioids and skeletal muscle relaxants are useful therapy when combined with NSAIDs for acute low back pain," Friedman said.
A quarter of people who come to the ER with low back pain receive NSAIDs and opioids, and another quarter receive NSAIDs and muscle relaxants, while 15 percent receive all three, Friedman told Reuters Health by email.
He and his colleagues studied 323 patients who arrived at the ER with low back pain that started within the previous two weeks.
Everyone in the study was instructed to take 500 milligrams of the NSAID naproxen (Aleve) twice daily.
In addition, the patients were randomly assigned to receive a 10-day course of either a dummy pill, the muscle relaxant cyclobenzaprine or the opioid oxycodone, to be taken every eight hours while pain persisted.
A week later, and also a month later, patient-reported measures of pain, function and use of health care resources were all similar regardless of the type of pain medication, the researchers reported in JAMA.
By seven days after the study began, almost two-thirds of patients in each group had improvements in pain level and function, though half reported some persistent functional impairment and more than half were still using medication.
By three months after the ER visit, almost a quarter of the group said they still felt moderate to severe pain requiring medication, but less than three percent said they had taken an opioid painkiller in the previous three days.
"Low back pain is very common," Friedman said.
"The classic mechanism of injury is lifting something too heavy," he said. "But some patients just slept in an awkward position, some twisted the wrong way, some were in minor car accidents, some didn't stretch before going to the gym."
Some of the medications ER providers rely on don't appear to do any good, he said.
"Though the results are perhaps not surprising, combination therapy of this sort is still very common," said Dr. Richard A. Deyo of Oregon Health and Science University in Portland, who was not part of the new study.
"This study may encourage more cautious use of opioids and muscle relaxants for acute back pain, resulting in fewer side effects and seemingly no loss of benefit," Deyo told Reuters Health by email.
"NSAIDs get us some of the way to relief," Friedman said. "We had hoped that opioids or skeletal muscle relaxants would get us the rest of the way," but they don't, he said.
Similarly, complimentary therapies like chiropractic, massage, acupuncture, stretching, yoga and exercise do not appear to provide additional benefit, he said.
"For patients who can't tolerate NSAIDs, muscle relaxants are very reasonable," Friedman said. "Opioids too may play a role in these latter patients."