Russell Hebets Feb. 22, 2011

Colorado Representatives Claire Levy and Mark Waller have just introduced a bill which would set a legal limit on the amount of THC that is permissible in a person’s blood while driving. HB 11-1261, introduced this week, proposes that a person with a blood content at or above 5 nanograms of THC be charged with DUI per se. The proposed bill follows the language of the current DUI per se law creating a permissible inference that an individual is Driving Under the Influence if his or her Blood Alcohol Content is greater than .08. Opponents of the law argue that this standard is arbitrary and puts valid medical marijuana users at risk of prosecution without any evidence that marijuana use has impacted their ability to safely operate a motor vehicle. There have been numerous studies which indicate that daily marijuana users are less affected by the cognitive and psychomotor impairment affects of THC than infrequent users (D’Souza et al. 2008; Hart et al. 2001; Jones et al. 1981; Ramaekers et al. 2009). H.B. 11-1261 allows individuals to be charged without any indication of impaired driving. 

Another potential problem with the proposed law relates to the length of time that marijuana stays in the blood of a daily user such as a medical marijuana patient. According to a study by the National Institute of Health, the half-life for delta 1-tetrahydrocannabinal is approximately 4 days. This means that a daily medical marijuana user could easily have the threshold level of 5 nanograms of THC in their system hours or even days after last using marijuana. 

Currently individuals taking other legal prescription medications (such as Xanax) on a daily maintenance schedule are not at risk of prosecution without a showing of an impaired ability to drive safely. There is no “per se” level of these drugs in their blood which triggers DUI or DUID charges. While it is an important and necessary goal to keep impaired drivers off Colorado’s roads, significant caution should be exercised before instituting a blanket law which would put many Coloradans who have serious and legitimate medical problems at risk of prosecution.