Yvonne Wingett Sanchez

The Republic | azcentral.com

Arizona voters approved a medical-marijuana program in 2010.

The program has about 40%2C000 participants and is overseen by the state Department of Health Services.

Supporters of the program have said the presence of certain metabolites alone should not constitute impairment under the law%3B prosecutors have disagreed.

Motorists who have used marijuana cannot be charged with driving under the influence on that basis alone, even if some traces of the drug are detected in their blood, the state's top court ruled Tuesday.

Arizona Supreme Court justices disagreed with the Maricopa County Attorney Office, which argued before the court in November, that drivers whose blood tests reveal the presence of an inactive marijuana metabolite known as Carboxy-THC can be prosecuted for driving while impaired.

Read:Arizona Supreme Court ruling

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The court was unconvinced the mere presence of the metabolite, which can remain in the bloodstream for 30days, is valid evidence of impairment.

The court wrote that marijuana users break the law if they drive while "impaired to the slightest degree" and if they are discovered with metabolites in their system that are known to impair. But, wrote Justice Robert Brutinel, drivers cannot be convicted "based merely on the presence of a non-impairing metabolite that may reflect the prior usage of marijuana."

The opinion affects motorists who use marijuana illegally, as well as the estimated 40,000 people who participate in the state's medical-marijuana program. Those cardholders are legally allowed to ingest pot to treat ailments ranging form chronic pain to glaucoma, and many of those cardholders have argued that traces of metabolites do not prove impairment.

Maricopa County Attorney Bill Montgomery said in a statement that the court had engaged in "interpretive jujitsu." The court should have asked the state Legislature to clarify whether it contemplated impairment based on the presence of a non-impairing metabolite, Montgomery wrote.

"By acting as it has, our State Supreme Court contributes to citizen cynicism particularly when it involves the whys and wherefores of drafting and passing legislation," he wrote. "Why should citizens work through our republican form of government and petition their duly elected legislators for statutory change when they can take a shot at only having to persuade just three Justices?"

The ruling stems from the case of Hrach Shilgevorkyan, who was pulled over for speeding and making unsafe lane changes. The driver admitted to smoking "some weed" the night before and volunteered to take a blood test, which revealed the presence of Carboxy-THC.

He was charged with driving with an illegal drug or metabolite in his body. A judge threw out the charges.

The Arizona Supreme Court concluded in Tuesday's ruling that interpreting the law so that any byproduct of cannabis proves impairment "leads to

absurd results."

"Most notably, 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," the Supreme Court's ruling said. "For example, at oral argument the State acknowledged that, under its reading of the statute, 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."

Additionally, the court wrote, "this interpretation would criminalize otherwise legal conduct."