In 1999, Washington State voters approved the legalization of medical marijuana. In November 2012, Washington voters passed Initiative-502 (I-502), legalizing retail cannabis sales and recreational cannabis use for adults 21 years and older. As with alcohol, the law provides two options for prosecuting suspected impaired drivers: 1) demonstrating impairment through detailed observation notes, field test results, witness observations, or Drug Recognition Expert assessments; and 2) determining the suspect’s blood level for the drug is above the legal “per se” limit. I-502 established a per se level of 5ng/mL of active delta-9-tetrahydrocannabinol (hereafter THC) in blood for cannabis-impaired driving. THC is a psychoactive compound in cannabis.
The objectives of this study were to examine drivers involved in collisions and/or arrested for suspected driving under the influence (DUI), who were investigated by the Washington State Patrol and for which blood evidence was collected in order to: describe the trends in THC involvement over time and in relation to the passage of I-502; to describe the prevalence of THC alone and in combination with alcohol and other potentially intoxicating drugs; and to describe the estimated time to blood draw under real world conditions, and examine the relationship between estimated time to blood draw and the level of THC detected. Additionally, to provide necessary context, law enforcement and toxicology testing procedures as well as arrests, stat patrol staffing levels, and training over the study period were documented.