Court: Pot-smoking drivers must show impairment before DUI citation

PHOENIX -- Arizonans who smoke marijuana can't be charged with driving while impaired absent actual evidence they are affected by the drug, the Arizona Supreme Court ruled Tuesday.

The justices rejected arguments by the Maricopa County Attorney's Office that a motorist whose blood contains the slight amount of a metabolite of marijuana, can be presumed to be driving while impaired and therefore driving illegally. They said the medical evidence shows that's not the case.

Tuesday's ruling most immediately affects the more than 40,000 Arizonans who are legal medical marijuana users. It means they will not be effectively banned from driving, giving how long the metabolite, Carboxy-THC, remains in the blood. It also provides protection against impaired driving charges for anyone else who drives and has used marijuana in the last 30 days, including those who might be visiting from Washington or Colorado, where recreational use of the drug is legal.

The case before the case involves a driver cited for a traffic violation who, when given a blood test, was found to have Carboxy-THC in his system and was charged with driving with an illegal drug or its metabolite in his body.

A trial judge threw out the charge. But the Court of Appeals said the laws on impaired driving "must be interpreted broadly.'

In arguments to the court, Susan Luder, a deputy Maricopa County attorney, acknowledged that Carboxy-THC, a secondary metabolite of marijuana, can show up in blood tests for a month after someone has used the drug. And she did not dispute the concession of her own expert witness that the presence of that metabolite does not indicate someone is impaired.

But Luder told the justices the Legislature is legally entitled to declare that a positive blood test for Carboxy-THC can be used to prosecute someone who, if convicted, can lose a driver's license for a year.

But Justice Robert Brutinel, writing the majority ruling, said that argument makes no sense.

"This interpretation would create criminal liability regardless of how long the metabolite remains in the driver's system or whether it has any impairing effect,' he wrote. Brutinel pointed out that Lunder admitted to the justices that, the way Arizona law is worded, "if a metabolite could be detected five years after ingesting a proscribed drug, a driver who tested positive for trace elements of a non-impairing substance could be prosecuted.'

And Brutinel noted that even prosecutors contend the metabolite itself does not cause impairment.

The judge also said that the position being taken by prosecutors "would criminalize otherwise legal conduct,' citing the 2010 voter-approved law allowing those with a doctor's recommendation to purchase -- and use -- up to 2 1/2 ounces of marijuana ever two weeks.

"Because Carboxy-THC can remain in the body for as many as 28 to 30 days after ingestion, the state's position suggests that a medical marijuana user could face prosecution for driving any time nearly a month after they had legally ingested marijuana,' Brutinel wrote.

"Such a prohibition would apply even when the driver had no impairing substance in his or her body.

Tuesday's ruling was not unanimous.

"The difficulty of detecting drug impairment justifies a flat ban,' wrote Justice Ann Scott Timmer in her dissent.

She said the evidence presented shows Hydroxy-THC, the psychoactive element in the drug, converts quickly to Carboxy-THC, "which is why law enforcement typically does not test blood for Hydroxy-THC.' What that means, she said, is that a motorist who tests positive for Carboxy-THC may or may not have had Hydroxy-THC in the blood while driving.

"The flat ban ensures that a driver who had an impairing substance in the body while driving is prosecuted even though that substances may have quickly metabolized into a non-impairing substance,' Timmer wrote.

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