Marijuana use among U.S. college students in 2016 was at the highest level seen in the past three decades, according to the most recent findings from the national Monitoring the Future follow-up study.

College student marijuana use has been showing a steady increase over the past decade.

In 2016, 39 percent of full-time college students aged 19-22 indicated that they used marijuana at least once in the prior 12 months, and 22 percent indicated that they used at least once in the prior 30 days. Both of these 2016 percentages are the highest found since 1987, and represent a steady increase since 2006, when they were 30 and 17 percent, respectively.

But the 2016 percentages are still below the peaks in use found in the early 1980s when 12-month and 30-day prevalence reached more than 50 percent and 33 percent, respectively (findings on college students were first available in the study in 1980).

Daily or near daily use of marijuana - defined as having used 20 or more times in the prior 30 days - was at 4.9 percent in 2016; this is among the highest levels seen in more than 30 years, though it has not shown any further rise in the past two years.

"These continuing increases in marijuana use, particularly heavy use, among the nation's college students deserve attention from college personnel as well as students and their parents," said John Schulenberg, the current principal investigator of the Monitoring the Future follow-up study. "We know from our research and that of others that heavy marijuana use is associated with poor academic performance and noncompletion of college.

"Colleges are not simply inheriting this problem from high schools. Marijuana use has remained steady in recent years among the nation's high school seniors, so this increase among college students suggests it has something to do with college and young adulthood experiences."

One likely reason marijuana use is increasing among college students and their peers who aren't in college, according to the study results, is the ongoing decline in perceptions of risk of harm from regular marijuana use. In 2016, 30 percent of those aged 19-22 perceived regular use of marijuana as carrying great risk of harm, the lowest level reached since 1980.

"This percentage peaked at 75 percent in 1991, when marijuana use among college students and their noncollege-age mates was at historic lows," said Lloyd Johnston, the original principal investigator of the Monitoring the Future study. "We have consistently seen this inverse relationship between perceptions of risks of harm and actual use, with changes in perceptions of risk typically preceding changes in use."

In 2016, 12-month and 30-day marijuana use were similar for full-time college males and females, but daily marijuana use was higher for college males at 6.6 percent than college females at 3.9 percent. Twelve-month and 30-day marijuana use tend to be lower among full-time college students than among their same-age peers who are not in college full-time. This is particularly true for daily marijuana use, with daily use among noncollege youth being two-and-one-half times as high - at 12.8 percent in 2016, the highest level since this panel study began in 1980 - versus 4.9 percent among full-time college students.

These findings come from the long term Monitoring the Future study, which has been tracking substance use of all kinds among American college students for the past 37 years. It is conducted by a team of U-M researchers and is funded by the National Institute on Drug Abuse. These results are based on full-time students who are one to four years beyond high school graduation and are enrolled in a two- or four-year college in March of the given year.