Has Marijuana Legalization Increased Marijuana Use Among US Youth?

Since 2012, citizens in Alaska, Colorado, Oregon, and Washingtonhave voted to legalize the recreational use ofmarijuana by adults. Advocates of legalization have argued that prohibition wastes scarce law enforcement resourcesbyselectivelyarrestingminorityusers of a drug that has fewer adverse health effects than alcohol.1,2 It would be better, theyargue, to legalize, regulate,andtaxmarijuana, likealcohol.3 Opponents of legalization argue that itwill increasemarijuana use among youth because it will make marijuana more availableatacheaperpriceandreduce theperceivedrisksof itsuse.4 Cerdáetal5haveassessed theseconcernsbyexamining the effects of marijuana legalization in Colorado and Washington on attitudes toward marijuana and reported marijuana use among young people. They used surveys fromMonitoring the Future between 2010 and 2015 to examine changes in the perceivedrisksofoccasionalmarijuanauseandself-reportedmarijuana use in the last 30 days among students in eighth, 10th, and 12th grades in Colorado and Washington before and after legalization.Theycomparedthesechangeswithchangesamong students in states in the contiguous United States that had not legalizedmarijuana(excludingOregon,whichlegalizedin2014). Theperceivedrisksofusingmarijuanadeclined inall states, but therewas a larger decline in perceived risks and a larger increase in marijuana use in the past 30 days among eighth and 10thgraders fromWashingtonthanamongstudents fromother states. They did not find any such differences between students in Colorado and students in other US states that had not legalized, nor did they find any of these changes in 12th graders in Colorado orWashington. If thechangesobserved inWashingtonareattributable to legalization,whywere there no changes found in Colorado? The authors suggest that this may have been because Colorado’s medicalmarijuana lawsweremuchmore liberalbefore legalization than those inWashington.After2009,Coloradopermitted medicalmarijuana to be supplied through for-profit dispensariesandallowedadvertisingofmedicalmarijuanaproducts.This hypothesisissupportedbyotherevidencethattheperceivedrisks ofmarijuanausedecreasedandmarijuanause increasedamong young people in Colorado after these changes in 2009.6