Tribune file

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 certain metabolite of marijuana can be presumed to be driving illegally because they are impaired. 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 legal protection against impaired driving charges for anyone else who drives and has used marijuana in the last 30 days, legal or otherwise, as well as provides a shield for those who might be visiting from Washington or Colorado, where recreational use of the drug is legal.

Maricopa County Attorney Bill Montgomery said Tuesday's ruling will result in roads that are less safe. He said if courts will not accept Carboxy-THC readings as evidence of impairment, then there is no way of knowing who is really “high” and who is not.

He said the record is there.

“We're seeing across the United States that where states have some form of medicalization or legalization of marijuana, the number of impaired drivers due to marijuana goes up,” Montgomery said.

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. He was charged under a state law which makes it illegal to drive 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 high 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 particular 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.

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.”

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

The judge also said that the position being taken by prosecutors “would criminalize otherwise legal conduct.” He pointed to 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.

Montgomery said the court should not have second-guessed the decision by lawmakers to make the presence of the metabolite proof of driving while impaired.

“We have a three-branch system of government in the state,” he said. Montgomery said those who believe someone who tests positive for Carboxy-THC should not be presumed impaired should have instead taken their case to the Legislature.

Montgomery conceded that the medical expert called by his office conceded that the presence of Carboxy-THC in someone's blood does not indicate that person is impaired. But he said that's irrelevant.

He said that it's easy to set a presumptive level of alcohol in the blood to indicate impairment because there are studies which show how rapidly it is absorbed in the body. That is not the case with marijuana.

“By ruling the way that the court did, we're actually inviting people to kind of ‘game’ when all active metabolites that might lead to impairment might be out of their system,” Montgomery said, and they could drive legally under Tuesday's ruling even though the blood test showed they had, in fact, used the drug at some point in the past. “And given the fact that people's judgment is impaired when they're under the influence of marijuana, there's no real way for them to know.”

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