Developing limits for driving under cannabis

doi:10.1111/j.1360-0443.2007.02009.x

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Wiley InterScience

Addiction

Volume 102 Issue 12, Pages 1910 - 1917

Published Online: 4 Oct 2007

Published on behalf of the Society for the Study of Addiction

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RESEARCH REPORT

Developing limits for driving under cannabis

Franjo Grotenhermen ¹ , Gero Leson ² , Günter Berghaus ³ , Olaf H. Drummer ⁴ , Hans-Peter Krüger ⁵ , Marie Longo ⁶ , Herbert Moskowitz ⁷ , Bud Perrine ⁸ , Johannes G. Ramaekers ⁹ ,Alison Smiley ¹⁰ & Rob Tunbridge ¹¹

¹ Nova-Institut, Hürth, Germany, ² Leson and Associates, Berkeley, USA, ³ University of Cologne, Germany, ⁴ Victorian Institute of Forensic Medicine and Department of Forensic Medicine, Monash University, Melbourne, Australia, ⁵ University of Würzburg, Germany, ⁶ Drug and Alcohol Services South Australia, Parkside, Australia, ⁷ University of California, Los Angeles, USA, ⁸ Vermont Alcohol Research Centre, USA, ⁹ Maastricht University, the Netherlands, ¹⁰ Human Factors North Inc., Toronto, Canada and ¹¹ Transport Research Laboratory, Crowthorne, UK

Correspondence to Franjo Grotenhermen, Nova-Institut, Goldenbergstrasse 2, 50354 Huerth, Germany. E-mail: franjo.grotenhermen@nova-institut.de

KEYWORDS

Accident risk • adverse effect • cannabis • driving • drug • DUIC • DUID • limit • marijuana • Psychomotor impairment

ABSTRACT

Objective Development of a rational and enforceable basis for controlling the impact of cannabis use on traffic safety.

Methods An international working group of experts on issues related to drug use and traffic safety evaluated evidence from experimental and epidemiological research and discussed potential approaches to developing per se limits for cannabis.

Results In analogy to alcohol, finite (non-zero) per se limits for delta-9-tetrahydrocannabinol (THC) in blood appear to be the most effective approach to separating drivers who are impaired by cannabis use from those who are no longer under the influence. Limited epidemiological studies indicate that serum concentrations of THC below 10 ng/ml are not associated with an elevated accident risk. A comparison of meta-analyses of experimental studies on the impairment of driving-relevant skills by alcohol or cannabis suggests that a THC concentration in the serum of 7–10 ng/ml is correlated with an impairment comparable to that caused by a blood alcohol concentration (BAC) of 0.05%. Thus, a suitable numerical limit for THC in serum may fall in that range.

Conclusions This analysis offers an empirical basis for a per se limit for THC that allows identification of drivers impaired by cannabis. The limited epidemiological data render this limit preliminary.

Submitted 16 April 2007; initial review completed 12 June 2007; final version accepted 7 August 2007

DIGITAL OBJECT IDENTIFIER (DOI)

10.1111/j.1360-0443.2007.02009.x About DOI