(CNN) - Teens who use e-cigarettes and hookahs are more likely to use marijuana later.
That's according to a study published Monday in the Journal Pediatrics.
Researchers from the University of Pennsylvania and the University of Southern California surveyed more than 2,600 students at Los Angeles public high schools.
They asked the students, who were 14 years old and in ninth grade, if they had ever tried hookahs or e-cigarettes.
They did a follow-up survey in the fall of 2015 when the students were 16 years old and in 11th grade asking about marijuana use.
The researchers found that the students who had tried e-cigarettes when they were freshmen were three times more likely to have tried marijuana than those who had not tried e-cigs.
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