Marijuana Legalization and DUI/DWI Law

The impact of the decriminalization of pot on state DUI/DWI laws.

By , Attorney

A number of states—including California, Nevada, Oregon, Massachusetts, Maine, Washington, Colorado, Illinois, Michigan, Vermont, Alaska, and Washington D.C.—have now decriminalized at least some recreational marijuana use. The majority of states also have legalized marijuana for medicinal use.

So, how does the legalization of weed affect state DUI laws? Generally, it has no effect: Most states that have decriminalized marijuana haven't changed their DUI laws. But the laws of these states already covered driving while impaired by marijuana.

Per Se and Impairment DUIs

All states have two types of DUI charges: "impairment" and "per se." The difference between the two charges is how the prosecution proves the driver was "under the influence."

With a per se DUI, the prosecution just needs to show that the driver had a blood alcohol concentration (BAC) of .08% or more (.05% or more in Utah.) The thinking is that anyone who has a BAC of at least .08% is under the influence and shouldn't be driving. But most per se laws refer only to alcohol concentration—they don't prohibit driving with a certain amount of drugs in your system. So, a motorist who is under the influence of only marijuana typically can't be convicted of a per se DUI.

Impairment DUI charges, on the other hand, do apply to marijuana use. The focus of impairment laws is on how the drugs or alcohol affected the driver—not on which substance or the actual amount in the driver's system. And, if the driver is impaired, it doesn't matter whether the alcohol or drug use was legal. That's why states haven't had to change their DUI laws in the wake of marijuana decriminalization: A driver who ingests marijuana legally—but is impaired—can still be convicted of an impairment DUI.


All jurisdictions have an impairment DUI charge. But the degree of impairment the prosecution must prove to get a conviction varies by state.

In Nevada, for instance, prosecutors must prove the defendant, as the result of the drugs or alcohol ingested, was impaired "to a degree that [rendered him or her] incapable of safely driving or exercising actual physical control of a vehicle." And under Massachusetts law, a person is "under the influence" if the substance ingested by the person "diminished the [person's] ability to operate a motor vehicle safely."

Check with a local DUI attorney to find out the standard in your state.

"Per Se Marijuana" DUIs

A handful of states have adapted the per-se-DUI concept to drugged driving. In these states, motorists can be convicted of a per se drug DUI for driving with a certain concentration of drugs in their system.

Several states that legalized recreational marijuana use have a "per se marijuana" DUI charge. For example, Washington's DUI law has a provision that prohibits driving with a concentration of five nanograms or more of THC (the primary psychoactive ingredient in marijuana) per milliliter of blood.

Talk to a DUI Attorney

The consequences of a DUI conviction are serious, and DUI law varies by state. If you've been arrested for or charged with driving under the influence, get in touch with an experienced DUI lawyer. A qualified DUI attorney can explain how the law applies to the facts of your case and help you decide on the best course of action.

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