Rates of intentional overdose deaths, or suicides by an overdose of a medication or substance, have risen among 15- to 24-year-olds, according to a new study by researchers at the National Institute on Drug Abuse (NIDA). Rates have also increased among adults ages 75 to 84.

Overall rates of intentional overdose deaths have declined, researchers found. The study covered overdoses between 1999 and 2019, HealthDay reports. NIDA Director Dr. Nora Volkow, senior author on the study, said it is likely the rates of suicide by overdose have increased during the pandemic.

“The distinction between accidental and intentional overdose has important clinical implications, as we must implement strategies for preventing both,” Volkow said in a news release. “To do so requires that we screen for suicidality among individuals who use opioids or other drugs, and that we provide treatment and support for those who need it, both for mental illnesses and for substance use disorders.”

The study found about 5% to 7% of overdose deaths are recorded as intentional. Volkow said the number is probably higher, because it can be difficult to determine whether overdose deaths are intentional.