Just 1% of health care providers accounted for nearly half of all opioid doses and 27% of all opioid prescriptions in 2017, according to a new study.

The researchers say the findings suggest that efforts to reduce overuse of prescription opioids should focus strict limits on a small percentage of providers, HealthDay reports.

“Most prescriptions written by the majority of providers are below recommended thresholds, suggesting that most U.S. providers are careful in their prescribing,” the researchers wrote. “However, a small portion of providers account for a highly disproportionate proportion of opioids.”

Providers who prescribed high amounts of opioids and patients receiving high amounts of opioids persisted over time. This suggests that these providers have established relationships with their patients over multiple years, the researchers noted.