Marijuana use involved in more fatal accidents in Colorado

May 15, 2014

The proportion of marijuana-positive drivers involved in fatal motor vehicle crashes in Colorado has increased dramatically since the commercialization of medical marijuana in the middle of 2009, according to a study by University of Colorado School of Medicine researchers.

With data from the National Highway Traffic Safety Administration's Fatality Analysis Reporting System covering 1994 to 2011, the researchers analyzed fatal motor vehicle crashes in Colorado and in the 34 states that did not have medical marijuana laws, comparing changes over time in the proportion of drivers who were marijuana-positive and alcohol-impaired.

The researchers found that fatal motor vehicle crashes in Colorado involving at least one driver who tested positive for marijuana accounted for 4.5 percent in the first six months of 1994; this percentage increased to 10 percent in the last six months of 2011. They reported that Colorado underwent a significant increase in the proportion of drivers in a fatal who were marijuana-positive after the commercialization of medical marijuana in the middle of 2009. The increase in Colorado was significantly greater compared to the 34 non-medical marijuana states from mid-2009 to 2011. The researchers also reported no significant changes over time in the proportion of drivers in a fatal motor vehicle crash who were alcohol-impaired within Colorado and comparing Colorado to the 34 non-medical marijuana states.

Stacy Salomonsen-Sautel, Ph.D, who was a postdoctoral fellow in the Department of Pharmacology, is the lead author of the study, which is available online in the journal Drug and Alcohol Dependence. Christian Hopfer, MD, associate professor of psychiatry, is the senior author.

Salomonsen-Sautel said the study raises important concerns about the increase in the proportion of drivers in a fatal crash who were marijuana-positive since the commercialization of medical marijuana in Colorado, particularly in comparison to the 34 non- states. While the study does not determine cause and effect relationships, such as whether marijuana-positive drivers caused or contributed to the , it indicates a need for better education and prevention programs to curb impaired driving.

Explore further: Signs point to sharp rise in drugged driving fatalities

Related Stories

Signs point to sharp rise in drugged driving fatalities

January 30, 2014

The prevalence of non-alcohol drugs detected in fatally injured drivers in the U.S. has been steadily rising and tripled from 1999 to 2010 for drivers who tested positive for marijuana—the most commonly detected non-alcohol ...

Marijuana use may double the risk of accidents for drivers

October 6, 2011

Over 10 million people age 12 or older are estimated to have driven under the influence of illicit drugs in the prior year, according to a 2009 National Survey on Drug Use and Health. While marijuana is the most commonly ...

Recommended for you

Drug against alcoholism works, researchers claim

March 17, 2017

French researchers provided fresh evidence Friday to support claims that a drug touted as a miracle cure for alcoholism, and prescribed for this purpose in France, actually works.

Should parents give their children alcohol?

March 10, 2017

Children and teens who are given alcohol by their parents are twice as likely to be drinking full serves of alcohol by age 15 or 16, but are much less likely to binge drink, a UNSW study shows.


Adjust slider to filter visible comments by rank

Display comments: newest first

4 / 5 (4) May 15, 2014
This is just bad science. Using the researchers' logic, the internet may be responsible for a huge proportion of fatal accidents. After all, over 80% of people killed in car crashes in 2011 had used the internet within 24 hours of their accident, up from virtually zero in 1994. In other words, the doubling in deaths from marijuana positive drivers may just reflect a doubling of use.

Next, the meaning of "tested positive for marijuana" is variable two ways. First, some states test for non-psychoactive marijuana breakdown products. Second, even if someone tests positive for an active marijuana metabolite, like THC, it does not necessarily indicate he was impaired. Many people can have trace amounts in their blood up to a week after exposure.

The article fails to mention the number of auto deaths, in Colorado and elsewhere, is going down. Some recent research has concluded some of the decrease is caused by people substituting marijuana for alcohol.

More problems but no more space here.
3 / 5 (2) May 16, 2014
The worst part of the article is the headline, saying 'use involved'...strongly implying it's causative. But later in the article it says "While the study does not determine cause and effect relationships, such as whether marijuana-positive drivers caused or contributed to the fatal crashes, it indicates a need for better education and prevention programs to curb impaired driving." So we have to give author partial credit for that. But the author also obviously doesn't know that marijuana use does not necessarily result in impairment. Impairment depends on how much is used, and how long after you've used. Use can actually INCREASE focus and competency after an hour or so for example. The only people that should be given any credibility about marijuana are those that are both educated, qualified, and have used pot enough to know how it works. And yes, no one should ever drive up to an hour after using a large dose of weed. But of course even many hours later they will test positive.
1 / 5 (1) May 17, 2014
"who tested positive for marijuana" Detected how? By measuring decarboxylated cannabinoids which are soluble in lipids and stay in your system for weeks? Or by hair which can go back quite a ways longer. Look marijuana can be dangerous for drivers- if they failed to pay attention to physics class and connect responsibility with the potential danger. What happened to the numbers of alcohol related ones and the overall trend?
1 / 5 (2) May 17, 2014
"Alcohol impaired performance relative to placebo but subjects did not perceive it. THC did not impair driving performance yet the subjects thought it had. These studies show that THC in single inhaled doses up to 300 g/kg has significant, yet not dramatic, dose-related impairing effects on driving performance. "
-U.S. Department of Transportation,
National Highway Traffic Safety Administration
(DOT HS 808 078), Final Report, November 1993:

"Thus, not only is it problematic to estimate the percentage of accident involvements associated with cannabis use alone, there is no evidence that impairment resulting from cannabis use causes accidents. Attempts to alleviate these problems by calculating risk of culpability for an accident (rather than the risk of having an accident) suggest that cannabis may actually reduce responsibility for accidents."
Department for Transport, "Cannabis and driving: a review of the literature and commentary (No.12)," (London, United Kingdom: May 2000).

"While the clinical significance of a 3% to 5% decrease in speed may be questioned, previous research suggests such a decrease will result in approximately a 7% decrease in all injuries and a 15% decrease in fatalities (Nilsson 1981)."
Anderson, Beth M.; Rizzo, Matthew; Block, Robert I.; Pearlson, Godfrey D.; O'Leary, Daniel S., "Sex differences in the effects of marijuana on simulated driving performance," Journal of Psychoactive Drugs (San Francisco, CA: Haight Ashbury Publications, March 1, 2010), Vol. 42, No. 1.

" Results showed that cannabis use was negatively correlated with nonfatal accidents, but these results can be attributed to changes in the amount of alcohol consumed. More specifically, the decriminalization of cannabis and the subsequent reduction in penalty cost, as well as a reduced purchase price of cannabis, made cannabis more appealing and affordable for young consumers. This resulted in more cannabis use, which substituted for alcohol consumption, leading to less frequent and less heavy drinking. The reduction in the amount of alcohol consumed resulted in fewer nonfatal accidents."
Laberge, Jason C., Nicholas J. Ward, "Research Note: Cannabis and Driving -- Research Needs and Issues for Transportation Policy," Journal of Drug Issues, Dec. 2004, pp. 980-1.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.