University of Michigan researchers say more U.S. college students are making a habit of using marijuana.

A study released Tuesday found that pot supplanted cigarettes last year as the smoke-able substance of choice among full-time undergraduates who light up regularly.

Just under 6 percent of full-time students surveyed for the annual "Monitoring the Future" study reported using marijuana at least 20 times in the previous 30 days, a frequency the researchers said made them daily or near-daily users.

By contrast, 5 percent of respondents indicated they smoked cigarettes that often.

Lead investigator Lloyd Johnston says 2014 marked the first time the study found that pot was consumed more routinely than cigarettes in the three-and-a-half decades that the university's Institute for Social Research has surveyed a nationally representative sample of college students.