The Effect of Cannabis Compared with Alcohol on Driving

Abstract

The prevalence of both alcohol and cannabis use and the high morbidity associated with motor vehicle crashes has lead to a plethora of research on the link between the two. Drunk drivers are involved in 25% of motor vehicle fatalities, and many accidents involve drivers who test positive for cannabis. Cannabis and alcohol acutely impair several driving-related skills in a dose-related fashion, but the effects of cannabis vary more between individuals than they do with alcohol because of tolerance, differences in smoking technique, and different absorptions of Δ 9 -tetrahydrocannabinol (THC), the active ingredient in marijuana. Detrimental effects of cannabis use vary in a dose-related fashion, and are more pronounced with highly automatic driving functions than with more complex tasks that require conscious control, whereas with alcohol produces an opposite pattern of impairment. Because of both this and an increased awareness that they are impaired, marijuana smokers tend to compensate effectively while driving by utilizing a variety of behavioral strategies. Combining marijuana with alcohol eliminates the ability to use such strategies effectively, however, and results in impairment even at doses which would be insignificant were they of either drug alone. Epidemiological studies have been inconclusive regarding whether cannabis use causes an increased risk of accidents; in contrast, unanimity exists that alcohol use increases crash risk. Furthermore, the risk from driving under the influence of both alcohol and cannabis is greater than the risk of driving under the influence of either alone. Future research should focus on resolving contradictions posed by previous studies, and patients who smoke cannabis should be counseled to wait several hours before driving, and avoid combining the two drugs.

Medical Marijuana and Driving: a Review

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Drugs of abuse among acute psychiatric and medical admissions: laboratory based identification of prevalence and drug influence

“…The method described in paper I does not take account of the facts that blood concentrations related to intake of a given dose of a drug will vary between individuals, and for a given blood concentration, the degree to which a drug influences behaviour or symptoms will also vary. Also, the calculation of blood drug concentration scores (papers I and IV) was based on an assumption of additive effects of psychoactive substances (172,173). Substances may, however, interact in different ways; it may be that e.g.…”

Per se drugged driving laws and traffic fatalities

“…Not surprisingly, simulator, drivingcourse, and etiological studies, which are typically based on police crash and medical examiner reports, provide strong evidence that alcohol consumption leads to an increased risk of collision (Kelly et al 2004;Sewell et al 2009). Drivers under the influence of alcohol tend to underestimate the degree to which they are impaired (MacDonald et al 2008;Marczinski et al 2008;Robbe and O'Hanlon 1993;Sewell et al 2009), drive faster, and take unnecessary risks (Burian et al 2002;Ronen et al 2008;Sewell et al 2009). …”

“…Alcohol impairs driving-related functions such as concentration, hand-eye coordination, and reaction time (Kelly et al 2004;Sewell et al 2009). Not surprisingly, simulator, drivingcourse, and etiological studies, which are typically based on police crash and medical examiner reports, provide strong evidence that alcohol consumption leads to an increased risk of collision (Kelly et al 2004;Sewell et al 2009).…”