The San Diego Union Tribune ran an article this morning about states setting legal limits for THC for marijuana in DUI cases. It discussed how Colorado is trying to legislate a per se level for THC–meaning if you drive with a certain number of nanograms of THC from marijuana in your body, then you’re guilty of a drug DUI. Obviously it’s hotly contested, as it has been and will continue to be in California.
The scientific truth is setting a per se level for THC is very, very difficult. First, marijuana is a drug, much like a prescription drug. And some develop a tolerance to that drug, so they don’t manifest the impairment. Second, THC has both active and inactive ingredients. So if the blood work is reading THC, the next question is whether it’s reading the active or inactive ingredient. Are we really going to convict drivers on an inactive ingredient?
In Ohio, Nevada and Washington legalized marijuana, and for Ohio and Nevada, the legal limit is 2 nanograms of THC per millilter of blood. Nevada, 5 milligrams. About a dozen other states, including Illinois, Iowa, and Arizona, set a zero tolerance for THC.
California remains with no per se limit. For any drug DUI in California, the Prosecution must prove beyond a reasonable doubt that the drug can impair driving to an “appreciable degree” and that you were in fact impaired by that drug. The law lays it out in California Vehicle Code 312, and in the Jury Instruction CALCRIM 2110. The California Appellate Court also addressed this issue in the case People v. Brenner (2010) 185 Cal.App.4th 791. “A drug is a substance or combination of substances, other than alcohol, that could so affect the nervous system, brain, or muscles of a person that it would appreciably impair his or her ability to drive a vehicle/operate a vessel) as an ordinarily cautious person, in full possession of his or her faculties and using reasonable care, would (drive a vehicle/operate a vessel) under similar circumstances.” This is from Jury Instruction, CALCRIM 2100.