Cannabis Field Sobriety Tests

As cannabis use becomes more commonplace, given state legalization efforts, a pressing issue is enforcement of impaired driving laws.  A new study published in JAMA Psychiatry, however, suggests high false positives rates are a problem with field sobriety tests for cannabis intoxication.  From an accompanying commentary:

In this issue of JAMA Psychiatry, Marcotte et al¹ report that field sobriety tests (FSTs) as administered by highly trained police officers are insufficient to detect cannabis-induced impairment in a double-blind, placebo-controlled, parallel randomized clinical trial involving a large sample of 184 cannabis users. Although the group receiving active doses of Δ-9-tetrahydrocannabinol (THC), the active ingredient in cannabis, performed worse on the FSTs as compared with the placebo group; about half of the participants in the placebo group were classified as impaired. These findings are in line with previous placebo-controlled studies that also reported high false-positive FST rates under placebo. The legal implication of these findings can be major given that FSTs are currently part of the evaluation protocol in North America to detect drivers who are cannabis impaired. Yet, the lack of sensitivity of FSTs to detect THC-impaired individuals does not come as a big surprise, as FSTs have primarily been validated to detect gross alcohol impairment at high (more than 0.10%) blood alcohol concentrations. To add to this problem, there is no cannabis equivalent of a breathalyzer to verify exposure induced impairment, as trace amounts of THC in biomarkers correlate poorly with cannabis-induced behavioral impairment.

The need for a reliable method to assess cannabis intoxication is desperately needed.