Colorado poised to approve marijuana blood-level limits for drivers DENVER - A marijuana blood-level limit for drivers is once again poised for approval in Colorado -- after two previous attempts to pass the bill failed. The Colorado House gave initial approval late Monday to a bill setting a limit of 5 nanograms of THC, the psychoactive ingredient in pot, per milliliter of blood. The House has had similar votes before. Last year the pot DUI bill was rejected in the Senate. And last week, the House was poised to again adopt the standard, but legislative work was stopped for a filibuster on a civil unions measure. Sponsors describe the marijuana DUI bill as an analogy to the blood-alcohol standard for drivers. Opponents say blood THC levels don't gauge impairment. The marijuana bill faces one more vote in the House.