PHOENIX — Authorities can’t prosecute Arizona motorists for driving under
the influence of marijuana unless the person is impaired at the time of the
stop, the state Supreme Court ruled Tuesday in the latest opinion on an issue
that several states have grappled with across the nation.
The ruling overturned a state Court of Appeals decision last year that upheld
the right of authorities to prosecute pot smokers for DUI even when there is no
evidence of impairment.
The opinion focuses on two chemical compounds in marijuana that show up in
blood and urine tests, one that causes impairment and one that doesn’t but
stays in a pot user’s system for weeks.
Some prosecutors had warned that anyone in Arizona who used medical marijuana
simply shouldn’t drive or they would risk facing DUI charges, a contention that
drew the ire of pot advocates who claimed this interpretation of the law
criminalized their legal use of the drug after voters approved it in 2010.
Tuesday’s state Supreme Court opinion removed that threat in explaining that
while state statute makes it illegal for a driver to be impaired by marijuana,
the presence of a non-psychoactive compound does not constitute impairment under
Twenty-one states and the District of Columbia allow medical marijuana use,
while two states, Washington and Colorado, have legalized the drug for
recreational use by adults over 21. Five other states this year adopted laws
that allow the use of nonpsychoactive marijuana compounds for at least some
conditions, such as epilepsy.
Some states required signs of impairment before someone can be charged with
driving under the influence of marijuana. Others have zero tolerance for the
presence of any marijuana in the blood, whether in the form of active compounds
that cause impairment or inactive compounds that don’t, while a few states have
limits for how much active marijuana can be in the system, designed to be
comparable to the .08-limit for drunken driving.
However, only eight of those states have laws that allowed a driver to be charged
with being under the influence for having even marijuana compounds in their
systems that don’t cause impairment, according to the Marijuana Policy Project.
Last year, the Michigan Supreme Court ruled that medical marijuana users should
have some protections and that police must show that a driver is actually
“under the influence” of the drug — meaning impaired — to seek criminal
Tuesday’s ruling arises from the case of an Arizona man who was stopped by
police for speeding and later acknowledged having smoked marijuana the night
before. Blood tests revealed marijuana compounds in his system, however, not the
form that causes impairment, according to court records.
He was charged with driving under the influence of a drug and operating a
vehicle with the presence of the drug’s metabolite in his system.
The state Supreme Court noted that the language of Arizona’s statute is
ambiguous and does not make a distinction between the marijuana metabolite that
causes impairment and the one that does not when determining whether criminal
charges are warranted. Prosecutors had argued that the statute’s reference to
“its metabolite” when referring to drug compounds detected in a driver’s
system covers all compounds related to drugs, not just those that cause
This interpretation “leads to absurd results,” the high court panel wrote.
“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
In a dissenting opinion, Justice Ann A. Scott Timmer wrote that the law helps
“enhance detection and prosecution of drugged driving” and should remain
unchanged. She suggested any constitutional challenges would be better addressed
on a case-by-case basis.
Maricopa County Attorney Bill Montgomery expressed disappointment with the
ruling, noting the court should have left such a decision up to the Legislature
Attorney Michael Alarid III, who represented the man charged in the
case, however, said, “we’re very pleased, and we’re very relieved that it’s finally
“This does have far-reaching impacts on medical marijuana patients,” he
added, “and it basically corrects an error in the interpretation of the law.”