MSACL 2018 US Abstract

Topic: Cannabinoids

The Prevalence of Marijuana in Suspected Impaired Driving Cases in Washington State

Brianna Peterson (Presenter)
Washington State Patrol

Authorship: Brianna Peterson and Fiona Couper
Washington State Patrol

Short Abstract

The prevalence of both active THC and its metabolite carboxy-THC (THCCOOH) detected in suspected impaired driving cases pre-legalization was compared to the prevalence post-legalization for the state of Washington.

Long Abstract


In December 2012, the possession and private use of limited quantities of marijuana and marijuana-products became legal in the state of Washington. At the same time, the state’s driving under the influence (DUI) statutes were amended to include a per se level of 5 ng/mL delta9-tetrahydrocannabinol (THC) in whole blood for drivers aged 21 years and older. This study examined blood toxicology results from all suspected impaired driving cases submitted by law enforcement officers from Washington state between the years 2009-2012 (representing the 4 years prior to marijuana legalization) and the years 2013-2016 (the years following marijuana legalization). Analysis of the data includes demographic factors such as gender and age, concentrations of THC and THCCOOH detected, and prevalence of combined use of marijuana with other drugs and alcohol.


Whole blood samples submitted to the WSP Toxicology Lab were screened by immunoassay for the presence of carboxy-THC (cutoff 10 ng/mL). Presumptive positive results were confirmed by liquid-liquid extraction. Briefly, 1 mL of sample is added to 2 mL of deionized water. 800 µL of 10% acetic acid is added followed by 8 mL of hexanes:ethyl acetate (9:1). The samples are rotated for 30 minutes followed by centrifugation at 2500 rpm for 15 min. The organic layer is then evaporated to dryness at 40°C. The sample is reconstituted with 100 µL of 50:50 acetonitrile:deionoized water. The extracts were analyzed by LC/MS/MS (Agilent 1260 Infinity coupled to an Agilent 6420 or Shimadzu LC-20 coupled to a SCIEX 3200). The autosampler injected 10 µl per run. The gradient consisted of mobile phase A: 0.1% Formic Acid in deionizied water and mobile phase B: Acetonitrile. The gradient went from 60%A, 40% B to 5%A, 95% B in 10 minutes. Two multiple reaction monitoring (MRM) transitions were monitored for each compound: THCCOOH-d3 (internal standard), 348.3 ->330, 302; THCCOOH, 345 ->299,193; THC-d3 (internal standard) 318->196, 123; THC 315-> 193, 123. The limit of detection is 0.5 ng/mL for THC and 2.5 ng/mL for THCCOOH.


In 2009-2012, the average percentage of cases positive for THC and carboxy THC was 19.1 % (range 18.2-20.2 %) and 27.9 % (range 26.3-28.6 %), respectively. In 2016, the percentages had increased to 33.6 % and 38.5%, respectively. In addition, combination use of alcohol and/or alprazolam with marijuana has increased.

Conclusions & Discussion

Legalization of recreational marijuana has increased the number of marijuana related DUI cases in Washington. As more states pursue legalization of recreational marijuana, it’s important to consider how this impacts the safety of our driving populations. Also, considerations for establishing a per se value for THC will be provided.

References & Acknowledgements:

Financial Disclosure

Board Memberno

IP Royalty: no

Planning to mention or discuss specific products or technology of the company(ies) listed above: