Almost 9,000 children and teens died from prescription and illicit opioid poisonings between 1999 and 2016 in the United States, a new study finds. During this time, the death rate nearly tripled, CNN reports.

The study, published in JAMA Network Open, found nearly 81 percent of the deaths were unintentional. Five percent of the deaths were suicides, while 2.4 percent were homicides. For children under age 5, almost one-quarter of the deaths were ruled homicides.

“While there was a decline in the death rates in 2008 and 2009 that corresponded with a decrease in prescribing trends, the rates are going up again,” lead author Julie Gaither of the Yale University School of Medicine said in a news release. “It’s due to a rise in heroin and synthetic opioid use among teens.”