But not all students think marijuana use on campus is so prevalent.
"I'm kind of surprised by [the results of the study], since it seems like not that many people at Harvard use marijuana," Cook said. "It's obviously here but it doesn't have nearly as much of a presence as alcohol."
The study found that marijuana use increased among most demographic groups, although it was highest at colleges in the Northeast and lowest at Southern colleges.
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Usage was higher among white non-Hispanics than any other ethnicity, and men used marijuana more than women, according to the study.
The report was based on the responses of more than 14,000 students at 119 four-year colleges in 40 states.