More than one out of three average Americans used a prescription opioid painkiller in 2015, despite growing concerns these medicines are promoting widespread addiction and overdose deaths, a new federal study shows.

Nearly 92 million U.S. adults, or about 38 percent of the population, took a legitimately prescribed opioid like OxyContin or Percocet in 2015, according to results from the National Survey on Drug Use and Health.

"The proportion of adults who receive these medications in any year seemed startling to me," said study co-author Dr. Wilson Compton, deputy director of the U.S. National Institute on Drug Abuse.

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"It's an awful lot of people who take these, mostly for medical purposes, but within that a significant percentage end up misusing them," he added.

The survey found that 11.5 million people, or nearly 5 percent of the population, misused prescription opioids they'd obtained through illicit means.

About 1.9 million Americans (0.8 percent) reported full-fledged opioid addiction.

Overall, the results indicate that the medical profession is doing a poor job of appropriately prescribing opioid painkillers, Compton said.

Previous studies have found "there's still four times the rate of prescribing there was 15 years ago," Compton said. "Even though the rates have leveled off, we have a long way to go in improving medical care so these are not as overprescribed as they are currently."

Many people receive opioids they don't need and pass them on to relatives who aren't getting the treatment they need for chronic pain, the researchers noted.

These painkillers are highly addictive and potentially deadly. The number of overdose deaths involving opioids has quadrupled since 1999, concurrent with the quadrupling of opioid prescriptions, according to the U.S. Centers for Disease Control and Prevention.

The survey defined prescription opioid misuse as people taking the painkillers without a prescription, taking larger doses than prescribed, or using the drugs to get high, Compton said.

Of those who misused prescription opioids, more than 50 percent got the medications as hand-me-downs from family or friends. Overall, nearly 60 percent of misuse involved taking opioids without a prescription.

"That tells us there are a lot of leftover medications," Compton said. "In many cases, physicians could write smaller prescriptions, or avoid them completely for those who benefit from ibuprofen or acetaminophen," for example, Motrin, Advil or Tylenol.

People misusing opioids most often do so in a sincere attempt to treat pain, according to their survey responses.

Two-thirds of those who misused opioids said they were motivated by relief from physical pain, while only one in 10 said they misused painkillers to relax or get high, the survey reports.

"That tells me we need to do a better job of assessing and treating pain," Compton said.

The broken system of prescribing opioids stretches back at least a decade, and has its roots in the belief that pain should be considered a "fifth vital sign" just as important as blood pressure, pulse, respiratory rate and level of oxygen saturation, said Dr. Jack Ende, president of the American College of Physicians.

"If patients were not totally rid of their pain, that implied the physician was not doing his or her job or really didn't care," Ende said. "That movement went way beyond proper medical care, so much so that there was a lot of overprescription of opioids for noncancer pain."

Physicians now are encouraged to prescribe lower doses of opioids for shorter periods of time, Ende said, and new laws allow pharmacists to choose to fill only half of a prescription.

Doctors need to adopt a stepped-care approach to pain management, said Dr. Karen Lasser. She's an associate professor of medicine and public health at the Boston University School of Medicine's Clinical Addiction Research & Education (CARE) Unit.

With this approach, doctors would first try to manage pain using nondrug means -- such as physical therapy, yoga or acupuncture -- or prescribe milder pain medications, including aspirin, ibuprofen or acetaminophen, Lasser said.

"There would be guidelines for all the medications you should try before you get to opioids," Lasser said.

In addition, patients should have to sign an opioid treatment agreement outlining the risks and benefits of such therapy, so they understand the potential for addiction, Lasser suggested.

Ende pointed out that the Affordable Care Act (Obamacare) is key to sorting out imbalances in opioid prescription.

People with health insurance can be properly diagnosed and covered for nondrug pain treatments -- like physical therapy -- "rather than scrounge for opioids," Ende said.

"At least we can exhale today knowing that Medicaid funding will not be cut imminently, because without Medicaid we have no chance of making headway" against the prescription opioid epidemic, Ende said. He added that insurance also helps cover treatment for addiction.

The National Survey on Drug Use and Health is a door-to-door survey that allows participants to log answers directly into a computer, providing anonymity that promotes honest responses, Compton said. About 51,200 people completed the survey interview for 2015.

The study was published online July 31 in the Annals of Internal Medicine.