The DUI statute in Arizona is found at ARS 28-1381. Under this law, there are two different ways that people can be charged with driving under the influence of drugs. Under 28-1381(A)(1), it is illegal to operate a motor vehicle while you are under the influence of any drug, alcohol, or inhalant when you are impaired to the slightest degree. If you consume marijuana and then drive your vehicle while impaired by it, you can be charged with a marijuana DUI under this law.
Under ARS 28-1381(A)(3), people can be charged with DUIs when they operate motor vehicles with any drug listed in ARS 13-3401 or its metabolite. This subsection is a zero-tolerance law because you can be arrested if you have any amount of a listed drug in your system, even if you are not impaired. Marijuana is one of the listed drugs, along with heroin, cocaine, methamphetamines, and prescription drugs when you do not have a valid prescription.
While marijuana is a listed drug for a DUI charge under ARS 13-1381(A)(3), ARS 36-2852(B) specifically states that a person who has marijuana or its metabolites in their system cannot be convicted of a DUI under this subsection unless they are impaired to the slightest degree.