College students who use marijuana regularly have lower grades — whether or not they think it affects them, according to a first-of-its-kind analysis of Minnesota student survey data.

Mean grade-point averages dropped from 3.33 to 3.01, comparing male students who didn’t use marijuana at all with students who used it daily. The comparable gap for female students was 3.4 to 3.18

Researchers at Boynton Health, the student health service at the University of Minnesota, conducted the analysis after seeing a significant increase in marijuana use in initial data from a 2018 student survey.

As lawmakers in Minnesota and other states consider legalizing marijuana for recreational use, they need to see this kind of data and understand the impact of the psychoactive drug, said Dave Golden, Boynton’s director of public health and communications.

“This has to be a factor in people’s minds when they’re taking a look at [legalization],” he said.

The analysis is based on Boynton’s survey of 10,579 students at the U and 17 other schools in the state. The survey tracks trends in student behavior — including academic performance, mental health, drinking and screen time — but it typically does not cross-reference the data to see how one behavior affects another.

The share of U students who consider themselves current users — meaning they had consumed marijuana in the month before the survey — increased from 13.5 percent in 2007 to 22 percent in 2018.

Boynton’s research director Katherine Lust then compared self-reported GPAs to student marijuana use and to alcohol use. While binge drinking had an association with lower grades, it was weaker than the link with marijuana.

College grades don’t shift much when researchers compare different student demographics or behaviors, Lust said. So even though the differences were small when they compared grades by marijuana use, she said the findings were striking.

“It’s hard to get GPA to move,” she said. “When GPA is moving, you really are actually seeing something.”

Lust said poorer grades were associated with marijuana use even when students didn’t think it was affecting their academic performance. The mean GPA was 3.0 for male students who used marijuana and thought it affected their grades, and 3.2 for users who thought that it didn’t affect their grades. But both were lower than the average GPA of 3.3 for nonusers, and the differences were statistically significant, she said.

Students weren’t surprised by the findings. One 20-year-old U sophomore, who spoke on the condition that he not be identified, said he believes his near-nightly marijuana use hurts his grades. But he gets As and Bs, he said, and is on path to graduate with an economics major.

“Basically, my view is that if you can’t smoke weed and accomplish everything that needs to be done, then you shouldn’t smoke weed,” he said, noting that he uses marijuana for social reasons and better sleep. He said he showed up high to a couple of classes his freshman year and realized he couldn’t perform well.

One problem with a permissive attitude toward marijuana on campus is that it can make it difficult for students who become addicted, or dependent on marijuana to deal with stress or untreated mental illness, said Samuel Worthington, a coordinator of Recovery on Campus (ROC), a student support group at the U.

Those students do see their grades plummet — or they drop out, he added.

“It might be harmless for a lot of students … but it’s not universally harmless,” he said. Those with addiction or dependency problems “often talk about academic dysfunction as one of the first things to … set in as an indication of a problem.”

Cause or correlate?

Boynton Health officials cautioned that their analysis shows an association — not that marijuana use causes lower grades. It’s equally possible that students with lower grades seek out marijuana. The data also didn’t identify coinciding factors. It’s possible that marijuana users are also heavier drinkers or have higher rates of depression, which could also affect academic performance.

Other research, though, has found the link as well. A Yale University study in 2017 found a sharp difference in grades between sober students and those who heavily consumed marijuana and alcohol.

University of Maryland researchers proposed a two-step link — that marijuana use is associated with skipping classes, and that skipping classes results in bad grades. However, their research in 2015 also suggested that marijuana use might reflect disengagement from college life, which could lead to skipping classes.

The Minnesota survey includes students from five U campuses, as well as other institutions such as Carleton College and Pine Technical & Community College.

Marijuana remains illegal in Minnesota for recreational use, but cannabis products in pill and liquid forms are permitted for certain medical uses.

Ten states have legalized recreational marijuana, and Forbes magazine named Minnesota as one of the states most likely to follow in 2019 due to changes in political leadership. So far this year, though, lawmakers have discussed more incremental changes, such as broadening medical usage or reducing criminal penalties.

If marijuana were ever legalized in Minnesota, the minimum age would almost certainly be 21, so it still wouldn’t be legal for most college students, said Pat Bradley, vice chair of the Minnesota NORML advocacy group.

However, Bradley questioned the importance of GPA, noting that many smart teens who experiment with marijuana come to view grades as a poor measure of intelligence.

“Is it an attitude change?” he asked. Maybe the students just “no longer [care] about GPA.”