The connection between marijuana and grades may sound obvious to our readers, but it’s a surprisingly hard subject to study with appropriate controls.
Fortunately for Americans who are sending their children to the pot wonderland that is the average campus – to say nothing of colleges in several states that have legalized recreational marijuana – the Dutch have accidentally done the work for us.
Stanford University Psychiatry Prof. Keith Humphreys (yes, the same guy) writes in The Washington Post that a Dutch border city’s decision to cut off rampant drug tourism created a near-perfect experiment.
The policy change left one group of Maastrict University students (citizens of the Netherlands) unaffected and cut off another group (non-Dutch students) from the legal marijuana in the city’s cannabis cafes:
The research on more than 4,000 students, published in the Review of Economic Studies, found that those who lost access to legal marijuana showed substantial improvement in their grades. Specifically, those banned from cannabis cafes had a more than 5 percent increase in their odds of passing their courses. Low performing students benefited even more, which the researchers noted is particularly important because these students are at high-risk of dropping out. The researchers attribute their results to the students who were denied legal access to marijuana being less likely to use it and to suffer cognitive impairments (e.g., in concentration and memory) as a result.
And because the foreign students had no say in losing access to pot – as opposed to the U.S., where they could vote in state elections for legalization – there’s no “chicken and egg” problem, says Humphreys, who has previously warned about legal pot’s likely effects on young and poor people.