The voters in four states – Nevada, Massachusetts, Maine, and our own state of California – approved the legalization of recreational marijuana for adults in those states in November 2016. That now makes eight states where pot is legal for adults and an additional 28 states where pot is legal for medicinal purposes only. Will marijuana legalization have any effect on the DUI laws in these states?

Not at all. No state has changed its DUI laws as a result of marijuana legalization. It remains illegal in all fifty states to drive while under the influence of any drug or chemical substance – legal or illegal – even if the drug was prescribed or purchased over the counter. Drivers charged for any reason with DUI in Southern California will need the counsel of an experienced Orange County DUI lawyer. In most states, there are actually two types of DUI charges – “impairment” and “per se” charges – although the difference is seldom discussed.

With a per se driving under the influence charge, the state simply needs to prove that a motorist was driving with a blood alcohol content (BAC) level at 0.08 percent or higher. The presumption is that any driver with that level of alcohol in the blood is under the influence and should not be driving. But the per se laws in most states deal only with alcohol. Thus, a driver who is impaired only by marijuana usually cannot be convicted of a per se DUI charge.


However, “impairment” DUI charges apply to marijuana and all other drugs. The focus of impairment DUI laws is the effect of drugs on the driver – not which drugs or how much. If a driver is impaired, the driver is guilty of DUI, and it does not matter if the alcohol or drug use was legal. That is why states – including California – have no cause to change their DUI statutes in the aftermath of cannabis legalization. A motorist who consumes marijuana legally – but then drives while under its influence – can still be convicted of DUI.

Impairment-focused DUI laws are in effect in all fifty states, but the degree or level of impairment necessary for a conviction differs from state to state. The law in Nevada, for example, says a driver cannot be impaired “to a degree that [rendered him or her] incapable of safely driving or exercising actual physical control of a vehicle.” In Massachusetts, a motorist is under the influence if the motorist has consumed a substance that “diminished the [person’s] ability to operate a motor vehicle safely.”

Only two states have applied the “per se” legal principle to marijuana in DUI cases: Nevada and the state of Washington. Washington prohibits driving with a concentration of five nanograms or more of THC (tetrahydrocannabinol, the active ingredient in marijuana) per milliliter of blood. Nevada makes it illegal to drive with two or more nanograms of THC per milliliter of blood or ten or more nanograms of THC per milliliter of urine.


California voters approved Proposition 64, the “Adult Use of Marijuana Act,” in November 2016, so many are now concerned that more drivers will be high on pot on California’s streets and highways. Nevertheless, legalization of cannabis for recreational use by adults will have no effect on the state’s DUI laws. California’s impairment-focused DUI law specifies that drivers in this state may not consume any substance that affects “the nervous system, the brain, or muscles as to impair to an appreciable degree the ability to operate a vehicle in a manner like that of an ordinarily prudent and cautious person in full possession of his faculties.”

Without a per se DUI law, how is marijuana impairment determined in California? Even scientists disagree on how best to measure marijuana impairment. Research shows that marijuana intoxication peaks about thirteen minutes after consumption and remains intense for about 45 minutes. However, THC can be detected in blood and urine even weeks after the user is no longer impaired. Frequent pot smokers will always have some level of THC in their blood, whether or not they are high. That is why there’s criticism of state per se laws regarding cannabis intoxication, and it is one reason why California does not have a per se pot statute.

Opponents of placing per se THC limits in California’s DUI laws include UCLA public policy professor Mark Kleiman, who says the state’s existing DUI law, which is focused on driver impairment, is the best way to keep the public safe from intoxicated drivers. In California, a determination that a motorist is impaired by pot may be based on a police officer’s observations and on the results of field sobriety tests. A California police officer who suspects that a motorist is too high to drive may ask for the assistance of a “DRE” or drug recognition evaluator, a law enforcement officer trained to detect drivers impaired by drugs other than alcohol.


The drug recognition evaluator looks for dilated pupils, a heightened pulse rate, the scent of marijuana, short-term memory loss, and other signs of a motorist’s impairment. If a California drug recognition evaluator determines that you were driving under the influence of marijuana – or any other non-alcoholic intoxicant – you will be arrested and charged with driving under the influence.

If you drive on California’s streets and highways, it’s always wise to review the basics of the state’s DUI laws. A conviction for even a misdemeanor first-offense DUI can send a driver to jail for up to six months in California. If the driver causes serious injuries or a fatality, a felony DUI conviction could mean years in prison. California police departments routinely conduct sobriety checkpoints to look for impaired drivers. This also applies to states like Pennsylvania, where if arrested, you will need the services of a Pennsylvania Criminal & DUI Defense Law Firm.

Of course, the best strategy for avoiding a DUI conviction is a simple strategy. If you plan on drinking – or smoking marijuana – don’t drive. Arrange in advance for a taxi, a rideshare service, a limo, a designated driver, or a room for the night. Still, if you make a bad judgment and you are accused of DUI – or if you are wrongly arrested and you’re innocent – you’ll need an experienced Orange County DUI lawyer to challenge the state’s evidence and witnesses – and to fight for justice – on your behalf.