Students are less likely to drink heavily in U.S. states that have legalized cannabis than in those that haven’t, a study shows.

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“The biggest takeaway from our paper is that problem binge drinking in college students who are 21 and over, changes after the implementation of recreational marijuana use,” says Zoe Alley, a Ph.D student at Oregon State University and one of the study’s authors.

The researchers defined binge drinking as having consumed five or more drinks at one time in the past two weeks. States that had legalized cannabis had six per cent decreased odds of binge drinking among students 21 and over.

The effect was seen only in students 21 and older as 21 is the minimum age for alcohol in all U.S states, and for cannabis in states where it’s been legalized.

“Once you turn 21 in states without marijuana legalization, alcohol suddenly becomes very easy to come by, relatively speaking, so people might switch to that,” says Oregon State psychology professor David Kerr.

Under prohibition, both cannabis and alcohol are illegal for underage users, but available to some extent anyway. After they turn 21, alcohol is suddenly much more available than cannabis, making that the drug of choice for many.

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“When you reach the legal drinking age, suddenly a lot of people transition to using more alcohol because now it’s more available and marijuana is not,” Alley explains. “When you change that, so that marijuana is legal, we might see less of a substitution.”

On the other hand, if cannabis and alcohol are more or less equally available from legal sources — as in Oregon — fewer people turn to alcohol, leading to less problem alcohol use.

“In Oregon, there are lots of (cannabis) retail shops, and it’s advertised,” Kerr says. “We see it on billboards. The shops are very obvious in the way they are painted and displayed. It seems very available.”

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Canadian provinces nearly all have lower ages for legal consumption of both alcohol and cannabis. Would the effect seen at 21 in the U.S. appear similarly in Canada, but at a lower age? Alley thinks it would.

“My opinion, based on the data that I’ve seen, is that in Canada it would stick with the legal age,” she says. “I think what we’re seeing here is that people are expanding, or substituting, substances based on availability and convenience. Legality changes that.”

If cannabis use replaces at least some heavy drinking, is that a public health win?

“I think it’s too soon to tell,” Alley says.

“There are a lot of problems with binge drinking on college campuses — we’re talking about sexual assault, drunk driving, alcohol intoxication and lethality. If you can get that to go down, that’s clearly good.”

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“The public health implications of prolonged marijuana use are still being researched, and are less understood.”

The paper was published recently in the journal Addictive Behaviours. It used ten years’ worth of data from a survey of American university students that had 1.1 million participants.

With legalization in Canada, cannabis is becoming more-or-less as available as alcohol, not including issues like a lack of retail stores in some provinces.

The Oregon study aside, what effect does easy access to cannabis have on alcohol consumption? It’s not completely clear, and it may take a generation to work itself out.

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So far, there’s little sign of legalization cutting into alcohol sales in general, though some argue that fast-acting cannabis beverages, which are just starting to be available, are the product that might change that.

Academic studies of the relationship have had contradictory results, with some showing legalization decreased alcohol consumption, some that it increased it, and others showing no obvious connection.

In any case, experts see cannabis as not as harmful as alcohol — a lower percentage of users end up addicted, for one thing, and alcohol is associated with a range of health problems from cancer to liver disease.

In late 2018, about half of self-reported cannabis users polled said they would drink less under legalization, though a pollster we talked to at that time pointed out that there are ” … differences between what we think we’re going to do and what we’re actually going to do.”

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