Young adults under age 35 account for half of emergency room visits due to nonmedical prescription drug use, according to a new study.

Nonmedical prescription drug use is defined as use without a prescription or use for reasons other than for which the medication is intended.

In the study, researchers from the Centers for Disease Control and Prevention reviewed national data to identify which medications caused the highest numbers of emergency room visits following nonmedical use, Medical Express reports.

They found harm from nonmedical use of medications led to about 360,000 emergency room visits in the United States in 2016. The most frequent causes of these visits were benzodiazepines and opioids, most commonly in combination with other substances such as illicit drugs and alcohol. Forty percent of patients required hospitalization, the researchers reported in the American Journal of Preventive Medicine.