A new study from the University of Michigan finds that levels of first-time marijuana use among college students are at a 30-year high.
The study, published in the American Journal of Public Health, says 51 percent of college students ages 19 to 22 became first-time marijuana users in 2015. That's up from 41 percent in 2014 and 31 percent in 2013.
Study author Richard Miech says college students are about 50 percent more likely to become pot users than their peers who aren't enrolled in college.
"College is a time when there's no parental supervision, there's lots of free time, there's often a party culture, and so these things can promote experimentation with drugs," Miech said.
Miech says shifting attitudes toward recreational marijuana as more and more states opt to legalize it have likely contributed to the increase.
"I think what's happening is that people are beginning to see marijuana more like alcohol—that it's something you can do recreationally and that there's not much immediate harm from it," he said.