Back and neck pain afflicts millions of American adults, driving many to seek relief from their family doctor or even the local emergency room.

When these episodes of pain are acute and nonspecific — meaning there's no clear cause or explanation — it's generally advised to start off with everyday remedies like over-the-counter anti-inflammatories, and alternatives like heat therapy, massage or exercise.

If that's not doing the trick though, doctors may prescribe a short course of opioids, with the goal of relieving pain and improving a patient's function.

But the results of a rigorous clinical trial published Wednesday cast doubt on using opioids even in this situation.

In a study of more than 340 patients suffering from low back or neck pain, a team of Australian researchers found there was no difference in pain severity after six weeks between those who received opioids versus a placebo sugar pill.

"It was quite a surprise to us," says Andrew McLachlan, dean of pharmacy at the Sydney Pharmacy School and an author on the study, which was published Wednesday in The Lancet. "We thought there would be some pain relief, but overall there was no difference."

What's more, the study found those who received opioids had an elevated risk of misusing the drugs a year later, reinforcing the potential harms of turning to opiods for pain relief, even temporarily.

While previous research has focused on treating chronic pain with opioids, this study is notable because it examines garden-variety back pain that lasts a shorter period of time, at most three months.

"It's going to call into question a lot of the major guidelines that we have about how to treat people's back pain," says Dr. Mark Bicket, an anesthesiologist at the University of Michigan and director of research on opioids and pain.

Some experts already worry the surprising results could be misconstrued to suggest that opioids don't work for acute pain more broadly and caution that limitations to the study should be considered before generalizing too much.

"My guess is this will be a landmark study that will be cited a lot," says Dr. Samer Narouze, the past president of the American Society of Regional Anesthesia and Pain Medicine. "But I'm concerned that it will be used or weaponized to deny patients with acute pain from needed opioids," such as those in pain from severe injuries and post-operative pain.

No meaningful difference from placebo

The results of the new trial draw attention to an unexpected gap in our understanding of how well opioids work in the context of acute back pain.

Patients who had new low back or neck pain for 12 weeks or fewer were recruited from more than 150 primary care clinics and emergency departments in Sydney, Australia, and randomly assigned to either the opioid group or the placebo group. The study took six years to complete.

Patients were excluded from the study if they had serious spinal pathology, which could be related to injuries like a fracture, an illness, or a surgery, among other things.

The study focused on acute-onset back pain, which can be caused by everything from twisting or turning awkwardly to how you sleep, says McLachlan. For this type of nonspecific pain, he says, "you can't really take an X-ray and say, 'This is the problem.' "

Participants didn't know if they were receiving the medication or a placebo. The opioid group received a combination of oxycodone and naloxone, a medication that had the effect of minimizing gastrointestinal side effects related to the opioids, particularly constipation, so that participants wouldn't realize they were in the treatment group.

Naloxone, a drug used to treat overdoses, reverses the effects of opioids when given intravenously, under the skin or as a nasal spray, but not when given orally because it doesn't reach the blood supply, says McLachlan.

At six weeks, there was no significant difference in the pain scores between the two groups. The same was true after 12 weeks.

McLachlan says they focused on pain severity after six weeks because that would give enough time to gradually increase dosing until patients reached their optimal dose, up to 20 milligrams of oxycodone a day.

Prior research indicates that opioids can have a small but detectable effect on relieving chronic pain, McLachlan says. "This trial fills the gap by showing, even though people may have moderate to severe low back pain, opioids don't seem to be the choice for them because they don't provide any benefit" over this shorter period of time.

And the study showed that taking opioids appeared to confer additional risk.

When participants were surveyed a year later to gauge whether they had certain risk factors for opioid misuse, 20% of those in the opioid group had a score indicating behaviors that a doctor would find problematic when prescribing opioids. That's compared to 10% in the placebo group.

Findings could stir controversy

The results are sure to stir up debate about how to treat patients who are dealing with bouts of acute back pain.

Medical guidelines in the U.S. already caution against using opioids as a first choice when treating patients with acute pain, but opioids can be recommended when those other forms of treatment are not working.

"It's a well-designed trial," says Richard Deyo, a family medicine doctor and an emeritus professor at Oregon Health and Science University. "It's going to ruffle feathers, and I think there'll be a lot of controversy."

The study underscores a significant blind spot in the evidence around the prescribing of opioids for acute back pain, says Deyo, so much so that it's somewhat shocking a study like this hadn't been done sooner.

"We thought we knew the answer," he says, "But as it often turns out, when we actually ask some of the most fundamental questions and go after a rigorous answer, we sometimes discover a surprise."

The results should not be applied to acute pain more broadly and should be replicated before decisions are made about modifying guidelines and "changing the care for thousands, if not millions of people," says Dr. Mark Sullivan, a professor of psychiatry and behavioral sciences at the University of Washington in Seattle.

"This is just one trial, but if its findings are true, then it looks like the benefits of opioid treatment for a back pain episode are less and the risks are higher than we've assumed," he says, noting the increased risk of opioid misuse among those who received opioids in the study.

A 'good' study, but how relevant?

Even with trial's careful design — considered the gold standard for studying treatment outcomes — the results don't necessarily reflect the full reality of treating acute pain in the U.S., says Dr. Narouze, chair at the Center for Pain Medicine at Western Reserve Hospital in Cuyahoga Falls, Ohio.

Rather than being offered short-acting opioids to take as needed, the treatment group received long-acting opioids in the trial and were instructed to take them twice a day, which he says "defeats the purpose for acute pain" because the goal is to give the patient pain relief quickly and when needed.

"The regimen they used was really unorthodox, at least in the United States," he says. "We do not treat acute pain with long-acting opioids."

Whether short-acting opioids would have made a difference isn't clear, but Narouze says the study's design doesn't make the findings applicable to situations when patients are on other opioid regimens.

The study also only applies to a very specific patient population — those with nonspecific back pain that started recently — which tends to be related to musculoskeletal issues, he says. "We cannot generalize this data to other pain groups," he says. "This is only one study, although it's a very good study."

University of Michigan's Bicket says it's clear that opioids work very well at relieving pain for short periods of time, for example after serious physical trauma or when recovering from surgery.

"Most of our questions are about is that benefit continuing and going to extend for pain that lasts beyond just a couple of days?" he says.

This study shouldn't be taken as the final word, but Bicket says it does add further weight to the idea that other treatments besides prescription opioids should be emphasized for low back pain.

"This one study won't rewrite the guidelines entirely," he says." I think it will motivate many future studies to be done both for back pain as well as for other conditions where we think prescription opioids may be appropriate."