Some patients prescribed opioids for pain relief after surgery may face a high risk for developing a long-term addiction to the medicine, a new study concludes.

The study included more than 36,000 surgery patients, who were followed for six months. None had taken opioids before their surgery. The researchers found 5 to 6 percent of patients continued to fill prescriptions for opioids long after what would be considered normal surgical recovery, HealthDay reports.

Rates of new chronic use did not differ between patients who had major or minor surgery, the researchers wrote in JAMA Surgery. This suggests patients continue to use these medications for something other than treating pain from surgery, they said.

Risk of long-term opioid use was highest among smokers, patients who had struggled with alcohol and/or drug use in the past, those previously diagnosed with depression or anxiety, and those who had a history of chronic pain.