Understanding when and how patients become long-term opioid users can go a long way in helping healthcare providers curb addiction. According to one study, though, a visit to the OR is rarely the start of it all.

Results from the research, published in a letter this month in JAMA Surgery, showed that instead, patients prescribed opioids who went on to receive the medication for months usually got their first prescriptions for back pain or other “ill-defined” ailments.

The research looked at 117,118 patients insured through the military who were prescribed narcotics for at least six months and found that 800 of them (0.7 percent) got their first prescription following an “inpatient encounter” while just 458 patients had an “inpatient procedure.”

“As we search for causes of the opioid epidemic, we note that hospital events and associated procedures do not appear to be the main drivers,” the authors wrote.

While the results suggest surgeons are rarely to blame for triggering long-term opioid use in their own patients, results from other studies suggest that they could be fueling the epidemic in another way: leftover meds.

The results of a study published earlier this month showed that about two-thirds of surgical patients didn’t use their full prescription. Very few of these patients properly dispose of these pills and often squirrel them away in case of an emergency. But other studies have shown that these unused pills are sometimes stolen or abused.

Surgeons often have a one-size-fits-all approach to prescribing post-op meds, leading to overprescribing. And unlike general care practitioners, surgeons still haven’t received national guidelines for prescribing opioids from the Centers for Disease Control and Prevention.

Opioid prescription rates have generally been decreasing in the U.S. since their peak in 2010. Yet, more than 33,000 overdose deaths in 2015 were linked to opioids, including prescription painkillers.