A Colorado children’s hospital reports visits by teens to its emergency department and satellite urgent care centers more than quadrupled after the state legalized marijuana, a new study finds.

Researchers examined the hospital’s records for 13- to 21-year-olds between 2005 and 2015. Colorado legalized medical marijuana in 2010 and recreational marijuana in 2014.

The annual number of visits related to marijuana or involving a positive marijuana urine drug screen more than quadrupled, from 146 in 2005 to 639 in 2014, the researchers found. They will present their research next week at the 2017 Pediatric Academic Societies Meeting in San Francisco.

“The state-level effect of marijuana legalization on adolescent use has only begun to be evaluated,” lead author George Sam Wang, MD said in a news release. “As our results suggest, targeted marijuana education and prevention strategies are necessary to reduce the significant public health impact of the drug can have on adolescent populations, particularly on mental health.”