(HealthDay)—The number of days supplied of an initial opioid prescription is the strongest risk factor for developing long-term opioid use among previously opioid-free injured workers, according to a study published online July 17 in JAMA Network Open.

Zoe Durand, Ph.D., from the Tennessee Department of Health in Nashville, and colleagues examined the prevalence and risk factors of long-term opioid use after injury among workers in Tennessee. Injured workers aged 15 to 99 years who reported only one injury to the Tennessee Bureau of Workers’ Compensation were identified.

Overall, 79.6 percent of 58,278 injured workers who received opioids after injury were opioid-free at the time of injury. The researchers found that 4.0 percent of opioid-free injured workers began long-term opioid use. Long-term opioid use correlated with receiving a supply of 20 or more days versus a supply of less than five days (odds ratio, 28.94) and visiting three or more versus one prescriber in the 90 days after injury (odds ratio, 14.91) after controlling for covariates. There was an increase in the odds of long-term use in association with a five- to nine-day supply compared with a supply of less than five days (odds ratio, 1.83).

“Developing long-term use appears to be more associated with prescribing practices, especially days’ supply of the initial prescription, than patient or injury characteristics,” the authors write. “These practices can be modified to reduce patient risk of overdose and associated morbidities.”