A new study finds the number of U.S. children entering foster care rose dramatically because of parental substance use between 2000 and 2017, HealthDay reports.

There were almost 5 million foster care placements between 2000 and 2017. Almost 1.2 million (about 23%) were home removals because of parental substance use, researchers report in JAMA Pediatrics. The number of foster care placements because of parental substance use rose from 14.5% in 2000 to 36.3% in 2017. “These factors coincide with increasing trends in opioid use and overdose deaths nationwide during this period,” the researchers wrote.

The study found children entering foster care because of parental substance use were more likely to be 5 years old or younger. They were also more likely to be white and from the South. The researchers also found an increase in drug-related removals in areas outside of cities.