The Great Marijuana Myth: Is Driving High Dangerous?

A recent study finds that drivers who smoke marijuana within a few hours of driving are more likely to get into an accident than sober drivers. Find out how much more.

Marijuana plant

Last week, the British Medical Journal published a study about the effects of smoking cannabis (aka marijuana, pot, weed, Mary Jane) on driving ability. Researchers at Dalhousie University in Nova Scotia, Canada, analyzed 9 prior studies and concluded that — contrary to most pot smokers’ beliefs — driving high leads to a higher risk of car accidents.

Now, before we go any further, let’s address the elephant in the room: pot is illegal in most states. But (as we know) people smoke it regardless of what the law says. However, no matter what folks tell you, driving under the influence of any controlled substance is illegal and dangerous.

We could write endlessly about reckless driving — drinking, using a cellphone, and even driving tired all put you and others at risk — but for our purposes today, let’s focus on Dalhousie’s study and the specific dangers of smoking pot and driving.

Weed and driving effects

Turns out, drivers who smoke marijuana within a few hours of driving are almost twice as likely to get into an accident as sober drivers. And though the accident stats aren’t as bad as they are for drinking and driving, the risk is palpable.

While alcohol is still the most common accident-inducing substance, a recent survey quoted on the National Institute of Drug Abuse’s Web site found that 6.8 percent of drivers who were involved in accidents — most of whom were under 35 — tested positive for THC (the chemical found in marijuana).

Smoking weed and driving laws

Unlike testing for alcohol levels, researchers and law enforcement officials have not yet determined how to accurately test for levels of marijuana intoxication. Many states, however, have begun to take a hard line on this public safety issue and police officers are now being trained to detect signs of marijuana intoxication. And make no mistake about it: driving a motor vehicle while under the influence of drugs — including legal-use marijuana — is illegal in all states.

Get a breakdown of drugged driving laws here.

The great marijuana myth

It’s possible you’ve heard a pot aficionado state:  “I’m a better driver when I’m stoned.” Not true. A major issue with drugged driving is that when you’re high (well, not you specifically, we know you’d never do that), you don’t always realize that your judgment is impaired. This is especially true for teenagers who are already at-risk drivers. Couple this with a few hits of ganja, and the buzz can become, well, killer.

Though it varies by person, it generally takes at least 3–4 hours to come down from a high. No amount of strong coffee or greasy food is going to sober you up faster.

Drinking and driving vs. smoking weed and driving

Most of us grew up hearing “don’t drink and drive,” but not nearly as much effort was put into preventing the combination of smoking pot and driving. Yet marijuana affects reaction time, spatial sense, and perception — all of which are crucial to safe driving. So when a person is driving high, they may end up following another car too closely (and brake too late), make unsafe turns, or misjudge road hazards.

The fact remains: weed and driving don’t mix

In the coming years, we may see a move toward the legalization of pot. But no matter where you stand on the issue — “a need for weed” or “not for pot” — we should all be on the same page when it comes to designating a driver who abstains from ALL mind-altering substances (legal or not).

If you’re into graphs and footnotes, you can read the whole British Medical Journal study here.

Related links

Driving on drugs: stats and facts
National Institute of Drug Abuse article on drugged driving
National Institute of Drug Abuse research report on marijuana abuse
CNN reports marijuana nearly doubles the risk of collisions
Dalhousie University report

321 Responses to “The Great Marijuana Myth: Is Driving High Dangerous?”

  1. Steven Verhulst
    December 28, 2012 #

    6.8% of what accidents? They don't blood test everyone who has an accident. They blood test you if they think you have been drinking. So 6.8% of people who had been drinking at the time of an accident had also smoked marijuana in the past 30 days. Which is probably the reason they had an accident? Alcohol or marijuana? Not marijuana! This is an insurance company blog and total bunk. They have no idea what they are talking about. If you people believe this crap I've got some swamp land in Florida I want to talk to you about. Total crap!

  2. Dean
    December 28, 2012 #

    It will make you a better driver, more alert, more attentive.

  3. Juan Lopez
    December 28, 2012 #

    so many flaws with this study already pointed out. people keep trying to "prove" that marijuana really is bad, now that the whole country is waking up. what they have been doing to people over the past half a century over marijuana is oppression, plain and simple. Marijuana is the safest, most natural drug we know of, even considering otc's like aspirin which cause liver problems, aneurysms, and etc. Alcohol kills so many people every year, but there are bars in every restaraunt. On the rare occasion someone has a wreck while stoned or with weed in their urine, it is assumed that the person was high while driving and that the accident happened due to weed. They never say whether the person was also drunk or high on meth or sleep deprived or in a psychotic/angry state, or any other number of factors. Been driving high for 10 years, and I have had 3 accidents all caused by sober people smashing into me because they were driving careless. Nothing every happened except they got a ticket. And yet, people will try to use bs studies like this to try defend the criminalization of people for possession of marijuana. Give it up big blue, people are tired of you and your bs. Your system is about to die.

  4. ru1
    December 29, 2012 #

    Well 52 yrs old and smoked weed since I was in the fifth grade. With good grades. And became a web press printer. Which prints newspaper with 40 units and get a load no accidents. The point is goverment su…

  5. Mara Mae
    December 29, 2012 #

    I've never in my 50 years known of anyone getting in an accident 'because' they were stoned. I do know several people on pain pills and other prescriptions that regularly get into accidents, a couple of them average 10-12 accidents a year and usually have their kids in the car. There is no testing for that and they are far more dangerous. They 'nod off' while driving… but that's ok I guess….

  6. Rob
    December 29, 2012 #

    As an advocate for Marijuana I would like to request that everyone here who is claiming how much they smoke and drive, please stop. I smoke. I think it should be legal. It causes accidents. You may be able to handle it, just like alot of people can handle drinking, but no matter what pro-pot or anti-pot funded 'scientific' studies say, it alters the mind. When we are driving we need to be in a clear state of mind. We are trying to make this legal. We are saying we should be able to smoke as 'responsible' adults. I beleive we should be able to smoke, but every time someone comes out demanding that they can smoke and drive with no problem you are only giving amunition to those that would like to keep this illegal. We are saying let us responsibly smoke. We must prove that we are responsible, or we will never get this on a federal level. We need to be responsible by not driving high, and if we refuse to, we really need to keep it to ourselves.

    • Juan
      January 3, 2013 #

      It does not alter the mind. Shrooms alter the mind. Marijuana raises your thc levels, in effect making you very happy and giddy. If you don't smoke alot and have low tolerance, then you will get very high, and probably shouldnt try to do anything let alone drive. People who smoke every day are not affected like this. It isn't like alcohol where you can still become incoherent by just drinking alot past your limit.

  7. nytola
    December 31, 2012 #

    Well, I love weed !! I love eating and smoking. I love sitting around a fire and smoking. I love watching my favorite funny movie while smoking. When I was a teenager I would smoke and drive and come to think of it – I was a horrible driver when I was high. I remember this one time where I looked down at my speedometer and I was going 20 ( in a 55.) Anyway my point is; enjoy life, experience life, go to Joshua tree and try mushrooms, go sky diving and do all the other crazy things you want. But don't do drugs and drive – its only our egos that tell us we are better drivers under the influence or our friends who want to justify their own decision to get in the car with you when your stoned ! They'll say things like " yeah john is crazy, its like the more beer he drinks the better driver he becomes " lol Anyway have an amazing new year – drunk, sober, high or tripping out, enjoy life while its here.

  8. andrew
    January 1, 2013 #

    That's why both accidents ive been in I've been sober an I almost always drive stone

  9. RD
    January 1, 2013 #

    Well, I've never smoked pot and don't think it should be legal (except for medicinal purposes). But, finally a voice of reason from the pro-pot crowd. While we can agree to disagree about using pot, at least you're sane enough to admit that smoking it and driving is a bad idea. THANK YOU.

  10. Hans Brickface
    January 2, 2013 #

    "6.8 percent of drivers who were involved in accidents — most of whom were under 35 — tested positive for THC"

    What about the drivers who actually CAUSED accidents?
    What about drivers who were in accidents and weren't tested?
    What about those who tested positive for THC, yet were not high at the time?
    Correlation is not causation. What if people who take THC just tend to be those who are also less experienced drivers?

    There is so much sloppy science nowadays and a lot of is biased due to the influence of government funding. It's simply not believable in my view.

    Also "pot is 2x more dangerous" may work for insurance purposes, but sadly real life is much more complicated with other factors like: distance driven, location of driving, time of day, traffic conditions, weather, emotional state, passengers, illness, and mechanical soundness to mention a few. Who is a bigger danger to the public, an angry teenager who drives high but only 1 mile per day or a judge with bad vision and the sniffles who drives 3 miles a day?

    Paraphrasing this article http://mises.org/daily/2343, the police should focus on violations of person and property, not scientific oddities like blood content. It is crazy to not know whether or not you are a criminal until after a tyrannical government performs its tests.

  11. Hemp Head
    January 2, 2013 #

    As I read through the many comments on this subject, and see how well all you long term term users are functioning, especially you Michael Daniels, I feel much better about pot in general, and the ability to operate a motorized vehicle while using. Beause I know I have driven druck, and I can proply operate a vehicle. I also agree that this is a wicht hunt and a misusess of power. The police have many suppies, which can keep some things from happeing, and impire their investigation. Noy Michael, this mite not be fare??

    Michael, I truly hope that you didn't get in a vehicle and drive after you posted the above comments? Children, it's good to know that after many years of using, Michael has such command of his thoughts, and can understand when to sop nad og???

  12. R Dawg
    January 2, 2013 #

    Tony, the PERSON that wrote this article wrote it, I think in part so that ignorant people like you might think about the consequences of driving high. She is in no way bashing or trying to give pot smokers a bad name, you're doing a fine job on your own by saying that you drive stoned. Face it! THC does have an affect on your mental state. Think about it……why do you smoke it in the first place? Cause you get HIGH! Be responsible and smoke all the pot you want and STAY home. Don't get behind the wheel! I don't wish anything bad on you but your habit may someday bite you in the ass and cause you to get into an accident and hurt someone or maybe even yourself. Why don't you try to talk to someone that was in an accident caused because they were high. Im sure they will tell you it isn't worth driving high. Pot affects different people differently, I know, I've tried it and I can't say I like it. It's not for me, but I know that in my "high" state, I was in no way capable of driving a car. Don't drive high. Have respect for people who are responsible….have respect for yourself.

  13. Steve Quinn
    January 2, 2013 #

    One of the effects of being "high", besides the munchies, is that a person's concentration is on one thing at a time. A pot smoker is so focused on one item that their reaction to another "event" is drastically slower. Being high and operating a motor vehicle is exactly the same as Russian Roulette.

  14. nailbiter
    January 3, 2013 #

    Everyone reacts differently to cannabis, and cannabis comes in varying strengths. Speaking from my experience, the study is correct: it slows one's reaction time and impairs judgment.

  15. James
    January 3, 2013 #

    Marijuana takes over one month to no longer come up as a positive in a drug test. So 6.8% of people in accidents smoked pot within the last 1-2 months. What does that prove? Maybe that 6.8 percent of drivers smoke weed in general?

  16. D G
    January 4, 2013 #

    This is such a joke! Whoever did this study is out of their minds! Anyone that thinks driving on pot has a better chance of getting into an accident is just plain stupid! I have been a pot smoker for more than 30 years. On and off again depending if I had to work which I do and never have to worry about drug testing. But I have not only driven a car most of that time, I also drive heavy machinery at work high everyday! I deliver parts to the area for production. What a joke. I have NEVER had an accident, not one time. Same thing with my car. So how do you account for that? It's NO accident! And it's like that for anyone well most anyone over 25, with a mortgage like me, a car like me, carry a gun permit like me. I pay my taxes every year. So put that study down and keep it in the UK where the people are stupid enough to fail at anything while on pot! Time to go burn one!

  17. Dick Chain Knee
    January 8, 2013 #

    Study is bogus. Its conclusions politically motivated.

    The facts:

    Note that urine tests do not detect the psychoactive component in marijuana, THC (delta-9-tetrahydrocannabinol), and therefore in no way measure impairment; rather, they detect the non-psychoactive marijuana metabolite THC-COOH, which can linger in the body for days and weeks with no impairing effects.

    Why not test for hamburgers? More than 6.8% of drivers in accidents will test positive for hamburgers. Should we ban hamburgers?

  18. Chanler
    January 10, 2013 #

    I've scoured the Internet and have yet to find a single traffic fatality linked SOLELY to marijuana. Not one. According to the National Highway Traffic Safety Administration, there are lots when marijuana & alcohol are BOTH present, but since there are plenty where only alcohol is involved, it seems a little far fetched to conclusively say the marijuana was a factor. They probably also had some food in their systems. Wonder if that was a factor?..And this article doesn't say if any of these people who had THC in their systems alone or if other substances present.

  19. fred
    January 10, 2013 #

    That's a bunch of bullcrap . Go back to the Uk ,48 more states to go weed nation. I rather smoke then drink behind the wheel . Where is the bud where is the bud ….

  20. tazman
    January 10, 2013 #

    Yes. Unequivocally.
    I have done both (I'm not proud, and I've paid consequences), driven drunk and driven stoned, and they both impair your vision and judgment while driving. Not recommended.
    That said, I do believe that marijuana is far less harmful than alcohol, and definitely not addictive in the same manner, and that if people can drink responsibly, they can smoke pot responsibly.
    Legalizing it and regulating it in similar fashion to alcohol (and taxing the heck out of it, and using it for plastics, clothing, paper, food, medicine, etc., etc.) makes so much sense, it's a no-brainer.