Arizona, which legalized medical cannabis in 2010, is home to a market packed with a variety of products. (Photo: Getty Images/iStockphoto)

PHOENIX — Since 2012, 11 states have legalized marijuana use for adults — which voters nationwide are considering on their ballots this year. Researchers are just beginning to understand the effects of those laws.

Colorado and Washington were the first states to legalize the drug, and California, the most populous state in the nation, followed them.

Among the most pointed concerns with legalization are whether it has caused more young people to use the drug and whether more people are dying in auto crashes caused by impaired drivers.

Data show little change in either area.

Surveys of young people in Colorado, for example, show a slight decline in the percentage of middle and high school students using the drug. In Washington, the rates have remained the same.

Opponents of legalization say the risk is too great if young people are given the impression that marijuana is not harmful, or if drivers become lax about getting behind the wheel when they are high.

States with legalized marijuana are finding more drivers impaired by the drug, but that comes in part because they are looking harder for it. Colorado, for example, did not track the level of marijuana impairment of drivers suspected of using it until 2016.

Washington saw an increase in drugged driving before legalization that continued after the drug was permitted, and has seen more fatal accidents with people on multiple substances. California data shows an increase in people driving while on drugs involved in fatal accidents.

But officials in those states are hesitant to peg the increases on legalization, and researchers haven’t shown an increase in total traffic fatalities tied to the changes. For example, California had 8.3% fewer traffic fatalities in 2018, the year retail marijuana sales launched there, than it did in 2017.

In Arizona, recreational legalization is on the ballot this fall. Supporters say the best way to mitigate impacts on society are to license and regulate the industry, funneling some of the new tax revenue back into programs to reduce usage by young people and combat impaired driving.

The state’s legislation would allow people 21 and older to possess one ounce of marijuana, not more than 5 grams of which can be a concentrated form of the drug. Adults also could grow six plants each in their homes, and the measure would license about 160 retailers to sell the drug.

South Dakota, New Jersey and Montana voters have similar measures on their ballots.

In Arizona, the proposed legislation also includes the ability for people previously convicted of minor marijuana crimes to have their records expunged, and changes requirements for law enforcement to cite drivers for operating a vehicle under the influence.

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No increase shown in teen use, but a change in perception

Among the major concerns with legalizing marijuana is that it would create a more