Stu­dents lost ac­cess to le­gal pot — and their grades im­proved

The Hamilton Spectator - - HEALTH - KEITH HUMPHREYS Keith Humphreys is a pro­fes­sor of psy­chi­a­try at Stan­ford Univer­sity Wash­ing­ton Post

The most rig­or­ous study yet of the ef­fects of mar­i­juana le­gal­iza­tion has iden­ti­fied a dis­turb­ing re­sult: Col­lege stu­dents with ac­cess to recre­ational cannabis on av­er­age earn worse grades and fail classes at a higher rate.

Econ­o­mists Olivier Marie and Ulf Zölitz took ad­van­tage of a de­ci­sion by Maas­tricht, a Dutch city, to change the rules for “cannabis cafés,” which le­gally sell recre­ational mar­i­juana. Be­cause Maas­tricht is very close to the bor­der of mul­ti­ple Euro­pean coun­tries (Bel­gium, France and Ger­many), drug tourism was pos­ing dif­fi­cul­ties for the city. Hop­ing to ad­dress this, the city barred non-ci­ti­zens of the Nether­lands from buy­ing from the cafés.

This pol­icy change cre­ated an in­trigu­ing nat­u­ral ex­per­i­ment at Maas­tricht Univer­sity, be­cause stu­dents there from neigh­bour­ing coun­tries sud­denly were un­able to ac­cess le­gal pot, while stu­dents from the Nether­lands con­tin­ued.

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 cafés had a more than 5 per cent 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.

Other stud­ies have tried to es­ti­mate the im­pact of mar­i­juana le­gal­iza­tion by study­ing those U.S. states that le­gal­ized medic­i­nal or recre­ational mar­i­juana. But mar­i­juana pol­icy re­searcher Ros­alie Pac­ula of Rand Cor­po­ra­tion noted that the Maas­tricht study pro­vide ev­i­dence that “is much bet­ter than any­thing done so far in the United States.”

States dif­fer in count­less ways that are hard for re­searchers to ad­just for in their data anal­y­sis, but the Maas­tricht study ex­am­ined sim­i­lar peo­ple in the same lo­ca­tion — some of them even side by side in the same class­rooms — mak­ing it eas­ier to iso­late the ef­fect of mar­i­juana le­gal­iza­tion. Also, Pac­ula pointed out that since vot­ers in U.S. states are the ones who ap­prove mar­i­juana le­gal­iza­tion, it cre­ates a chicken-and-egg prob­lem for re­searchers (i.e. does le­gal­iza­tion make peo­ple smoke more pot, or do pot smok­ers tend to vote for le­gal­iza­tion?). This method­olog­i­cal prob­lem was re­solved in the Maas­tricht study be­cause the mar­i­juana pol­icy change was im­posed with­out in­put from those whom it af­fected.

Al­though this is the strongest study to date on how peo­ple are af­fected by mar­i­juana le­gal­iza­tion, no re­search can ul­ti­mately tell us whether le­gal­iza­tion is a good or bad de­ci­sion: That’s a po­lit­i­cal ques­tion and not a sci­en­tific one. But what the Maas­tricht study can do is pro­vide highly cred­i­ble ev­i­dence that mar­i­juana le­gal­iza­tion will lead to de­creased aca­demic suc­cess — per­haps par­tic­u­larly so for strug­gling stu­dents — and that is a con­cern that both pro­po­nents and op­po­nents of le­gal­iza­tion should keep in mind.

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