Making Roadside Cannabis Use Testing Effective and Fair

Breathalyzers are extremely useful for detecting drunk driving. They allow rapid roadside testing that is accurate for answering the critical question: Is this person intoxicated right now? In contrast, urinalysis for detecting cannabis-intoxication in drivers has multiple liabilities. The test can’t be done at the roadside so the person has to be hauled in (perhaps unjustly) to a testing station. Also, a recent paper in the Journal of Analytic Toxicology points out another serious problem:

the typical target in urine is the inactive metabolite, [which is] less relevant with respect to impairment. In addition, drug metabolites become concentrated in urine and may be excreted for many hours, or days after use, and are less probative with respect to whether a person’s drug use was recent or more historical.

Tetrahydrocannabinol is lipid-soluble and regular pot smokers excrete it over time in their urine even if they haven’t smoked recently. As a result, a urine test could result in a cannabis-impaired driving conviction even though the person isn’t currently stoned. The JAT paper evaluated a different approach which may resolve these problems: Oral fluid sampling. The driver suspected of impairment is mouth swabbed at roadside and the saliva is placed in a machine, which rapidly prints out a result. This technology is fairer than urinalysis because it is only sensitive to recent marijuana use rather than use that happened a day ago or a week ago.

Of the devices the researchers tested in the study, the Dräger Drug Test 5000 (pictured above) had the best results. Assuming it doesn’t cost a mint, this technology could be a breakthrough for law enforcement as well as an important civil rights protection for people suspected of drug-impaired driving.

[Cross-posted at The Reality-Based Community]

Keith Humphreys

Keith Humphreys is a professor of psychiatry at Stanford University. He served as a senior policy advisor at the White House Office of National Drug Control Policy from 2009 to 2010.