Non-fatal drug overdoses increased for children under the age of 15 between 2016 and 2019, according to a study published in Pediatrics.

The increase appears to be due largely to stimulants such as cocaine, meth and Ecstasy, CNN reports. Overall, drug overdoses in this age group are rare, and are largely unintentional, the researchers noted.

The findings come from an analysis of almost 90 million emergency room visits for youth up to age 24. The researchers found suspected heroin overdoses among 15- to 24-year-olds dropped between 2016 and 2019.

The rate of drug overdoses involving all drugs for children ages 11 to 14 increased an average of 2.3% per quarter during that time. The average quarterly rate rose 1.9% for opioid-related overdoses and 4.3% for stimulant-related overdoses.