Having surgery always comes with risks. And a new study suggests one to add to the list: the risk of becoming a long-term opioid user.

About 6 percent of people who hadn't been taking opioids before an operation but were prescribed the drugs to ease postsurgery pain still got the drugs three to six months later, the study finds.

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That's long after the window considered normal for surgical recovery, say the authors of the national study, published in JAMA Surgery. The rate didn't differ between patients who had minor or major surgery. It was slightly higher in Southern states.

It was also 12 times higher than the rate of long-term opioid prescription filling seen in a control group of similar adults who didn't have surgery during the study period.

The researchers, from the University of Michigan Institute for Healthcare Policy and Innovation, found that certain factors made some "opioid-naïve" surgery patients more likely to refill opioid prescriptions for months afterward.

Those who had been smokers or were diagnosed with alcohol, drug, depression, anxiety or chronic pain conditions before their operations had a higher rate of persistent prescriptions.

This suggests other reasons that patients might keep up opioid use months after an operation, the researchers say — despite a lack of evidence that the drugs help chronic pain or other long-term issues.

A new surgical risk factor?

More than 50 million surgical procedures happen in the United States every year. If the study's findings hold true for all patients, that would mean about 2 million to 3 million people who were "opioid naïve" before surgery end up receiving the drugs for months afterward each year.

"This points to an underrecognized problem among surgical patients," says Chad Brummett, M.D., the first author of the study and director of the Pain Research division in the U-M Medical School Department of Anesthesiology. "This is not about the surgery itself, but about the individual who is having the procedure and some predisposition they may have. And we know that continued opioid use is probably not the right answer for them."

SEE ALSO: Why U.S. Doctors Love Opioids and Hate Marijuana for Chronic Pain

The team continues to study the issue in hopes of developing better processes for surgical teams to predict and manage the risk of long-term opioid use among their patients. The researchers launched an effort to help surgical teams prescribe opioids appropriately in the weeks immediately before and after an operation or procedure.

"These results show the need for education of surgical providers, to understand when it's time to stop writing prescriptions for opioids and to refer patients for assistance from a chronic pain physician," says Brummett, who co-leads the effort, called the Michigan Opioid Prescribing Engagement Network, or Michigan-OPEN. "We need to be asking patients why they think they still need opioids and what they're being used for, not just refilling."

He also notes that the study doesn't look at what happened to the unused portion of opioid medications in the initial prescriptions written for most surgical patients. Unless disposed of properly, which the U-M team has shown can be difficult, the drugs can end up in nonmedical uses.

About the study

The team reviewed data from more than 36,000 nonelderly adults with private insurance who had only one operation in a two-year period from 2013 to 2014. None had an opioid prescription in the year preceding the operation.

About 80 percent of the patients in the study had minor operations, to remove varicose veins, hemorrhoids, appendixes, prostates, thyroids and gallbladders, or to address hand issues, often through minimally invasive techniques. The rest had major operations such as bariatric surgery, hysterectomy, hernia repair or surgery to address severe reflux or remove part of the colon.

On average, the patients received a prescription for 30 to 45 tablets of opioids in the weeks immediately before or after the operation. Many surgical practices preapprove such prescriptions during the preoperative period so patients can fill them before they go to the hospital and have them on hand when they get home.

For the 6 percent or so who were still filling opioid prescriptions three to six months after the operation, the average number of postsurgery prescriptions was 3.3, adding up to about 125 pills. Other research has shown that long-term prescription opioid use raises the risk of becoming drug-dependent for nonmedical reasons and of using illicit opioid drugs such as heroin.

Smokers and those who had a history of alcohol or drug issues were about 30 percent more likely to keep filling prescriptions. People with arthritis were more than 50 percent more likely.

Brummett notes that new chronic pain is a known risk of surgery and that some operations require opioid use for more than a week or so to control acute pain. Surgeons may worry that if they limit opioid prescriptions, it will lower the patient-satisfaction scores that can affect how much insurers pay or cause their staff to have difficult interactions with patients.

But as a physician who specializes in treating pain, he points to Centers for Disease Control and Prevention guidelines that clearly state that opioids are not appropriate first-line medications for long-term pain control.

The data came from Institute for Heathcare Policy and Innovation's store of anonymous private-insurance claims data purchased from Optum. The Michigan Department of Health and Human Services, the National Institutes of Health and the Agency for Healthcare Research and Quality funded the study.

The comparison group included a randomly selected 10 percent sample of adults who did not have surgery or an opioid prescription in a one-year period. The researchers assigned them a fictional "surgery date" and looked for any opioid prescriptions filled in the 180 days after that.

"To truly confront our nation's opioid issues, we need to move upstream toward a preventive model that focuses on the 80 percent of our surgical patients who are not taking opioids," Brummett says. "From our interactions with surgeons and their teams through Michigan-OPEN, it's apparent that it's still a new idea to many that the prescription they write for a surgery patient is a potential source for new chronic use and even diversion of opioids. Surgeons and their teams want to do the right thing, so we need to help them shepherd patients through the surgical path and help them come out healthier."