The Supreme Court of Arizona decided this week to overturn a really stupid lower court ruling. The lower court had held that you could be convicted of driving while impaired by marijuana even if you weren't impaired by marijuana.
Yes, the lower court of appeals had previously held that if you had any amount of marijuana's non-impairing metabolite in your system, that you could still be convicted of driving while impaired. And that could happen weeks after you had last consumed the drug. The AZ supreme court wasn't having any of that nonsense.
If you have read our page on marijuana and driving, and driving, you know that your body converts THC into carboxy-THC. Carboxy THC has no impairing effect on your body. It is a benign substance that doesn't get you high, but stays in your body for weeks. So in effect, the lower court of appeals ruled that if you smoked marijuana, you couldn't drive for weeks afterward.
The Supreme Court decision removed the threat of arrest against someone who had smoked pot weeks before, by ruling that impairment means impairment, and that the authorities had to prove actual impairment, and not just remote consumption of marijuana, in order to sustain a conviction for DUI.
Twenty-one states and the District of Columbia currently allow medical marijuana. In addition, two states--Washington and Colorado--have legalized recreational marijuana. The State of Florida will be voting on medical marijuana in this November's election.
The Arizona Supreme Court case followed a Michigan Supreme Court decision last year that also held that the state has to prove some level of impairment in order to convict a citizen of driving while impaired.