There are two main types of laws in the United States pertaining to drugs in a person’s system while driving. They are effect-based DUID and per se DUID laws. Effect-based means being visibly impaired can get you into trouble if drugs probably made you impaired. Per se drug laws are those that can get you in trouble if there is a certain amount of measured drugs in your system.
Colorado recently implemented per se DUID laws. The law in Colorado says that you are too high to drive if you have more than 5 nanograms of THC per millileter of blood in your system. However, many experts debate whether this is a good measure of whether a person has the ability to drive safely.
Marijuana users and advocates say that there is not enough evidence to say what level of THC makes someone impaired. Medicinal marijuana, and soon legal recreational marijuana users, may find that they are consistently above the 5 nanogram limit, but don’t feel that they are impaired.
If someone is convicted of a driving under the influence of drugs law in Colorado, they might face similar penalties to those from a drunk driving conviction. A recent report cites the National Highway Traffic Safety Administration’s website that says it is inadvisable to use THC concentrations to predict a person’s ability to drive a vehicle, because not enough evidence is available to determine if these concentrations are accurate. Someone who is arrested for a DUID law might be wise to speak with an attorney.
Source: Business Insiders, “Why It’s Crazy To Try To Set DUI Limits For Marijuana,” Erin Fuchs, Dec. 19, 2013