Arizona Republic:  “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 the court’s opinion in the case of Arizona vs. Hrach Shilgevorkyan.