Drug Recognition Expert (DRE) examination characteristics of cannabis impairment.
BACKGROUND
The Drug Evaluation and Classification Program (DECP) is commonly utilized in driving under the influence (DUI) cases to help determine category(ies) of impairing drug(s) present in drivers. Cannabis, one of the categories, is associated with approximately doubled crash risk. Our objective was to determine the most reliable DECP metrics for identifying cannabis-driving impairment.


METHODS
We evaluated 302 toxicologically-confirmed (blood Δ(9)-tetrahydrocannabinol [THC] ≥1μg/L) cannabis-only DECP cases, wherein examiners successfully identified cannabis, compared to normative data (302 non-impaired individuals). Physiological measures, pupil size/light reaction, and performance on psychophysical tests (one leg stand [OLS], walk and turn [WAT], finger to nose [FTN], Modified Romberg Balance [MRB]) were included.


RESULTS
Cases significantly differed from controls (p<0.05) in pulse (increased), systolic blood pressure (elevated), and pupil size (dilated). Blood collection time after arrest significantly decreased THC concentrations; no significant differences were detected between cases with blood THC <5μg/L versus ≥5μg/L. The FTN best predicted cannabis impairment (sensitivity, specificity, positive/negative predictive value, and efficiency ≥87.1%) utilizing ≥3 misses as the deciding criterion; MRB eyelid tremors produced ≥86.1% for all diagnostic characteristics. Other strong indicators included OLS sway, ≥2 WAT clues, and pupil rebound dilation. Requiring ≥2/4 of: ≥3 FTN misses, MRB eyelid tremors, ≥2 OLS clues, and/or ≥2 WAT clues produced the best results (all characteristics ≥96.7%).


CONCLUSIONS
Blood specimens should be collected as early as possible. The frequently-debated 5μg/L blood THC per se cutoff showed limited relevance. Combined observations on psychophysical and eye exams produced the best cannabis-impairment indicators.
Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, 251 Bayview Boulevard Ste 200 Rm 05A721, Baltimore, MD, 21224, USA. Electronic address: rebecca.hartman@umaryland.edu.
Rebecca L
RL
Hartman
Hingham Police Department, 212 Central Street, Hingham, MA 02043, USA. Electronic address: jack.richman@comcast.net.
Jack E
JE
Richman
International Association of Chiefs of Police, 44 Canal Center Plaza, Suite 200, Alexandria, VA 22314, USA. Electronic address: hayes@theiacp.org.
Charles E
CE
Hayes
Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, 251 Bayview Boulevard Ste 200 Rm 05A721, Baltimore, MD, 21224, USA. Electronic address: marilyn.huestis@gmail.com.
Marilyn A
MA
Huestis
D000293:Adolescent; D000328:Adult; D002188:Cannabis; D016022:Case-Control Studies; D000066448:Driving Under the Influence; D013759:Dronabinol / Q000097:blood; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D015813:Substance Abuse Detection; D016138:Walking; D055815:Young Adult
D013759:Dronabinol
Cannabis; Driving; Drug Evaluation and Classification Program; Drug Recognition Expert; Impairment; THC