Despite a dramatic increase in opioid prescriptions in the past two decades, a new federal study says there is no good research to guide doctors on the risks or effectiveness of their long-term use for ailments such as back pain and osteoarthritis.

Dr. Erin Krebs admits that she and fellow experts on a federal task force assigned to evaluate the research were stunned.

“The bottom line is, the research hasn’t been done,” said Krebs, medical director of the Women Veterans Comprehensive Health Center at the Minneapolis VA.

“I expect when I’m making a major medical decision that someone could give me some numbers,” Krebs said. “We still can’t do that for opioid therapy. It’s sad, and I think it’s shameful we don’t have more research on this.”

About 20 years ago, doctors began expanding their use of opioids such as morphine, oxycodone and hydrocodone for the treatment of chronic, non-cancer pain, reasoning they had a moral obligation to help their patients.

In recent years, however, the widespread use of prescription opioids has sparked alarm: Their use was declared an epidemic in 2007 by the U.S. Centers for Disease Control and Prevention, and the government reported in 2011 that more than half of the nation’s 41,340 drug overdose deaths were related to pharmaceuticals.

In Minnesota, 200 people died from overdosing on prescription pain relievers in 2013, according to the Department of Health.

Krebs, an investigator with the VA’s Center for Chronic Disease Outcomes Research and an associate professor at the University of Minnesota, was one of the experts who analyzed 39 studies on opioid use since 2008. The study was commissioned by the Agency for Healthcare Research and Quality, a branch of the U.S. Department of Health and Human Services.

Krebs said the U.S. Food and Drug Administration approved the use of opioids for chronic, non-cancer pain on the basis of studies that lasted no longer than 12 weeks.

She said there’s no research that would indicate who might be most at risk of addiction or abuse, or what the odds are of becoming addicted.

Now Krebs has a $1.3 million study underway comparing opioids and non-opioid pain relievers like naproxen sodium and gabapentin for veterans with back pain or osteoarthritis, with results expected in about two years.

At present, physicians might consider a patient’s history of substance abuse, a family history of substance abuse and environmental factors when developing care plans, and closely monitor those who take opioids.

“Back pain makes people miserable. If it’s going to relieve your back pain you’re going to take it,” Krebs said. “So the other question is, how likely is it to relieve your back pain in the long term? And … believe it or not — we don’t know the answer.”

The American Academy of Pain Medicine says there is no national consensus for treating chronic pain not due to cancer. Most opioids provide some relief for acute pain, said Dr. Lynn Webster, immediate past president of the academy, who was not part of the task force. Problems arise, he said, with their long-term use. Most people find that they’re not very effective after a year or two.

“I don’t think there is anyone who would disagree that opioids are not the best therapy for most chronic, non-cancer pain,” Webster said. “For those who do benefit, we should not deprive them of that unless we can find an alternative that is safer and more effective.”