A new study finds 34% of young adults reporting misusing their prescriptions for psychoactive medications, including opioids, stimulants, tranquilizers and sedatives, CNN reports. More than 20% of teens who took these substances also said they misused them, the researchers report.

The researchers defined misuse as taking a prescription in larger amounts than prescribed, more often than prescribed, for longer than prescribed or in any way that was not specified by their health care provider.

Misusing psychoactive substances can lead to overdoses, chemical dependency and even death, said lead researcher Israel Agaku of the Harvard School of Dental Medicine.

The study found taking multiple psychoactive medications greatly increased the chance of misuse. More than 60% of young adults who took more than one psychoactive drug reported misusing at least one of their prescriptions. Among teens, more than 46% with multiple psychoactive prescriptions reported misusing at least one.