Smoking Marijuana Nearly Doubles Risk Of Driving Accidents

While it might seem obvious, researchers Mark Asbridge, Jill A. Hayden and Jennifer L. Cartwright took the trouble to scientifically conclude that “acute cannabis consumption is associated with an increased risk of a motor vehicle crash, especially for fatal collisions.” They report their findings in the British Medical Journal – here’s the abstract:

Objective To determine whether the acute consumption of cannabis (cannabinoids) by drivers increases the risk of a motor vehicle collision.


Design Systematic review of observational studies, with meta-analysis.

Data sources We did electronic searches in 19 databases, unrestricted by year or language of publication. We also did manual searches of reference lists, conducted a search for unpublished studies, and reviewed the personal libraries of the research team.

Review methods We included observational epidemiology studies of motor vehicle collisions with an appropriate control group, and selected studies that measured recent cannabis use in drivers by toxicological analysis of whole blood or self report. We excluded experimental or simulator studies. Two independent reviewers assessed risk of bias in each selected study, with consensus, using the Newcastle-Ottawa scale. Risk estimates were combined using random effects models.

Results We selected nine studies in the review and meta-analysis. Driving under the influence of cannabis was associated with a significantly increased risk of motor vehicle collisions compared with unimpaired driving (odds ratio 1.92 (95% confidence interval 1.35 to 2.73); P=0.0003); we noted heterogeneity among the individual study effects (I2=81). Collision risk estimates were higher in case-control studies (2.79 (1.23 to 6.33); P=0.01) and studies of fatal collisions (2.10 (1.31 to 3.36); P=0.002) than in culpability studies (1.65 (1.11 to 2.46); P=0.07) and studies of non-fatal collisions (1.74 (0.88 to 3.46); P=0.11).

Conclusions Acute cannabis consumption is associated with an increased risk of a motor vehicle crash, especially for fatal collisions. This information could be used as the basis for campaigns against drug impaired driving, developing regional or national policies to control acute drug use while driving, and raising public awareness.

[Read the full report in the British Medical Journal]


Majestic is gadfly emeritus.

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37 Comments on "Smoking Marijuana Nearly Doubles Risk Of Driving Accidents"

  1. w/e, if you are that burnt, you are too paranoid and would be driving 10mph or slower. i call bullshit.

  2. I’m not too surprised that driving baked is not ideal, but I have a question about the report. It states that “Acute cannabis consumption is associated with an increased risk of a motor vehicle crash…”
    What constitutes “acute” consumption? Does this mean driving after a casual toke, or driving while stoned out of your mind? There’s a big difference between the two, and it would be useful to know where the line is.
    Which is not to say that I’m in the habit of driving baked. I’m just wondering if this is one of those cases where they conflate extreme use with casual use to tar all pot smokers with the same brush.

  3. justagirl | Feb 10, 2012 at 11:37 am |

    yesterday i drove home very safely.  however, i attempted to unlock the house with the key fob for the car.  lol.  i literally pointed it at the lock.  when that didn’t work i tried opening it with my work key.  sigh.  eventually i got into the house and decided to switch to wine.

  4. Dane Collins | Feb 10, 2012 at 11:45 am |

    I remember reading a study that indicated the exact opposite.  I still would recommend staying home while high… who wants to harsh their buzz with traffic anyway?

  5. What kind of shit were these people smoking.  I delivered pizzas for 3 years, never got in any accident; nor outside of delivering, just daily driving.  I guess I’m not the “acute” smoker I thought I was.  Maybe I need to smoke more so I can prove that this study is true : P

    • madison34 | Feb 11, 2012 at 3:41 pm |

      My husband got his bachelors degree stoned and i was not and dropped out of college. Now I have regrets of not being stoned.

  6. Ceausescu | Feb 10, 2012 at 11:58 am |

    2 x 2 = 4

    Why am I saying that ? Because you prolly have 1-2 % chance to have an accident while sober. Marijuana doubles the chances ? REALLY ?

    Majestic is a sad human being who shouldn’t be allowed to post here anymore. We should vote or something :/

    Also, there was this study which showed that the decriminalization of marijuana  would decrease the number of driving accidents, violence etc. ( study was made in portugal )

  7. concerned toker | Feb 10, 2012 at 12:07 pm |

    Someone correct me if I’m wrong, but isn’t this study fundamentally flawed? To my knowledge, it is impossible to measure “acute” cannabis consumption without being present during the consumption, which is why there is no curbside toxicology test for cops to administer for DUIs.
    So they could be measuring cannabis use from weeks prior to the incident… hardly “acute” consumption.

    • I would take “acute” cannabis consumption as something like being stoned out of your mind, and whatever that subjectively means to you, I wouldnt want to be driving when i’m messed up enough to be impressed by inane and distracting things.

  8. compare the risk factor to alcohol, or prescription pills. Then base which one is more dangerous. Try texting and driving or talking on the phone and driving…what are the increased risk of those? Just because something impairs your driving skills doesn’t mean it is bad. You are not supposed to drive drunk, but DUI deaths are pretty high. Did they factor in driving conditions such as weather? Was the person alone or in a car full of people? They bases it on toxicology reports which we all know weed stays in your system for 28-30 days after doing it. So those toxicology reports could show that the person was high 2 weeks ago, but base it that they were high at the time of the accident.

  9. Someonesname | Feb 10, 2012 at 12:27 pm |

    this research is bulllshiit… i call bullshit as well..british people are full of bullshit 

  10. there is a link right above these comments that says pot reduces traffic deaths, ugh! the featured study is BS

  11. Before ever having puff in my life I read a shitton of books/reports on the consumption of marijuana, both pro and con. I guess the corporate tools who conducted this whitewash of a study should tell the FBI their description of a person driving under the influence of marijuana is inaccurate as the FBI said to look for someone going at or below the speed limit, following all traffic laws.


  12. Drinking alcohol also raises risk of car accidents.  Perhaps we should criminalize that too.

  13. discusthrower | Feb 10, 2012 at 2:24 pm |

    hmm… then there is this article that says medical marijuana laws reduce traffic fatalities..

  14. i can’t bother reading that
    but did the study take into account any other drugs and/or alcohol?

  15. Dingdingchomp | Feb 10, 2012 at 3:50 pm |

    umm so does texting, taking on the phone, and eating while driving ect. I’d like to see this side by side with these statistics. Not saying everyone should drive high but lets be realistic. anything can be dangerous while driving but how dangerous compared to everyday things. 

  16. OregonGrowQueen | Feb 10, 2012 at 5:07 pm |

    Well DUH! Gee I wonder how much the government paid for all those studies- I could of told you that! Dumbasses! 

  17. Ask any stoner and they’ll tell you they drive better under the influence. As a sober observer, however, you will learn that what they really meant is that they drive really, really, really slow.

    I’d also like to bring up the confounding variable that people in the UK can’t drive worth shit.

  18. When is the last time a stoned driver hit a non moving object (a tree, parked car….). Doing anything while driving that takes away from absolute concentration is not good but comparing it to drunk driving is BS. What next? Listing to the radio while driving? Lets compare that one.

  19. In other news, Reefer Madness 2012 comes out in theaters this Friday.

  20. Marihuana is very dangerous…. do NOT DRIVE or operate heavy machinery while under the influence!!
    This is a WARNING!!! repeat

  21. Micah Dylan | Feb 11, 2012 at 3:28 am |

    this is bullshit but nice image .. that looks like some dankass weed & i like the woodpipe too ..  spark it up & take a drive it’s all good baby baabie

  22. Sirius Fnord | Feb 11, 2012 at 3:53 am |

    Ok people we drive around in the equivalent of moving bombs(cars) knowing that we are putting our selves in a dangerous situation and maybe if it were just us on the road then we could compensate for the dangers. However there are millions of other people also driving lethal weapons and last time i checked one can’t be at all sure what kind of attention they are paying to their driving.

    So in short shouldn’t the article just read Driving a car increases your risk of death period.

    Oh and in respect of your article. No actual experiment was run, rather they just gathered together limited inconclusive evidence from fatal accidents that have occurred. Where upon one did not know the state of mind of the driver at the time and how almost any stimulant could affect it.

    Be a good scientist and always do your own verification and analysis. Do not allow others to make your mind up for you.

    Have a great day all

  23. Just because this study is relatively unbiased doesn’t mean that the studies they took data from were not. You need to have good data to come up with reliable statistics. And, they didn’t say whether or not the nine studies they selected were chosen at random…which is a critical step when minimizing bias in statistics. 

  24. Just Wondrin | Feb 13, 2012 at 12:36 pm |

    “Acute cannabis consumption” is the key phrase here.

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