Study Shows Marijuana Use Has ‘Little Effect’ on Driving Skills

Marijuana use had little effect on simulated driving skills, according to a Hartford Hospital study, but test subjects were more easily distracted when under the influence of the drug.

Investigators from Hartford Hospital and the University of Iowa Carver College of Medicine assessed the simulated driving performance of 50 male and 35 female subjects in a double-blind, placebo-controlled trial. All 85 subjects reported having used marijuana from one to 10 times per month previously.

The study was published in the March issue of the Journal of Psychoactive Drugs.

During the study, some subjects were given actual marijuana cigarettes, and some were given a placebo, with neither the investigator nor the subject knowing which they had smoked. Another administrator kept track of who was given which type of cigarette.

The marijuana was supplied by the National Institute of Drug Abuse and the University of Mississippi, the only legal source of the drug in the U.S.

Subjects drove a high-tech simulator that was very realistic, said Beth Anderson, an investigator in the study. “It was an actual car with parts replaced by computers.”

Participants then drove down a simulated country road for 15 minutes, first in an “uneventful” simulation, and then in collision-avoidance and distracted-driving simulations, the study states.

In the collision-avoidance portion, drivers reacted to simulated events such as another driver entering an intersection illegally, a changing traffic light, and a dog running into the road.

The researchers found no signifcant difference between the study groups in the collision-avoidance tests.


During the distracted-driving segment, participants solved “mental math” problems while driving, Anderson said. Subjects answered aloud simple math problems that were provided by a recording.

Speed and steering variability, as well as the number of errors made in the math portion of the test, were used to determine how impaired subjects were, according to Anderson.

“The study didn’t find a lot of impairment,” Anderson said. “[Subjects] slowed down. It looked like they were trying to compensate. Compensation would only take you so far.”

The study states that “participants receiving active marijuana decreased their speed more so than those receiving the placebo cigarette during a distracted section of the drive.”

Anderson stressed that the findings do not mean that driving high is harmless.

For instance, researchers noted that in the distracted-driving tests, “participants under the influence of marijuana failed to benefit from prior [driving]experience … as evidenced by a decrease in speed and a failure to show expected practice effects.”

“The results do not imply that it is safe to drive under the influence of marijuana, especially because we know people aren’t just smoking marijuana,” Anderson said. “They do it while drinking. They do this when others are in the car, listening to music, talking on cellphones or texting. These behaviors distract drivers and are even more dangerous when someone has been using marijuana.”

Anderson said the study showed that the effects of marijuana on driving need to be studied further.

“We need to know what marijuana does to the brain. We need to understand the ramifications. To create public policy and to keep people safe, you need to know what’s really happening in the brain,” Anderson said. “You have to have the facts.”

A 2004 fact sheet published by the National Highway Traffic Safety Administration said that marijuana has been shown to adversely affect driving.

“Decreased car handling performance, increased reaction times, impaired time and distance estimation, inability to maintain headway, lateral travel, subjective sleepiness, motor incoordination, and impaired sustained vigilance have all been reported,” the fact sheet states.

“Some drivers may actually be able to improve performance for brief periods by overcompensating for self-perceived impairment. The greater the demands placed on the driver, however, the more critical the likely impairment.”

– Article from The Hartford Courant.



  1. Anonymous on

    if you want to smoke a joint in your car, try to find a place where you can blend in. like a busy mall parking lot, also a good place to take hookers!
    dont try to hide somewhere, or a scenic place like a lookout or lake, ect.
    cops know where people like to hide and get high. when smoking a joint, crack only one window closest to you, smoke will travel where there is oxygen. after your smoke, dont save the roach and put in your ashtray, or anywhere else in your car. cops have iron noses, and can smell that lingering roach. finnish as much as you can, and throw it out! then crack all your windows when finnished. then light a cigarette or cigar this will neautralize the weed smell, do this even if you are not a tabbaco smoker. as you pull away turn on you air cond or fan full blast and keep the windows open. dont try to mask it with air freshners a shit like that, cops can detect this kinda cover up! better yet if you can keep driving well toking, and not get distracted, like burning a whole in your seat, lol. try back streets where there is not alot of traffic for easy task. very important, keep your smoke clouds to a minimum, and smoke it between your fingers like a cigarette. throw the roach out the window when finnished, very important! when transporting your stinky dro, put in an airtight tupperware container. also a good place is in a dirty bag of fastfood garbage, like in the cup, put the lid on it, straw intact, and put it at the bottom of the mess, and squirt kethcup all over the top of the mess crumple the bag up like you usually do, and throw it in the back somewhere. cops will tear your car apart, but they hate sticking there hand in dirty garbage! i strictly adhere to these rules and have never been comprimised!! i hope this blog will be usefull to all you stoners out there? if anybody can add to this, it would be welcomed!!! stay safe, peace-out, and for fuck sakes free marc emery!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  2. Anonymous on

    the feds don’t care if you drive fine a couple of hours after you smoke, they are training law enforcement as Drug Recognition Experts, they take regular police and give them a two week training course and send them out to stop you and draw your blood without probable cause, only their expert eyes.
    I am a medical cannabis patient in California and our dispensaries and patients are being watched and harassed while real crime goes on undaunted and with no deterrents. currently the law enforcement being funded by the feds is trying to leave medical cannabis patients unemployed and homeless by going after your driving privilege and your right to work. they think that if you choose a safe natural medicine like cannabis, then you should not have a right to work and live like a human being. I don’t smoke while driving and I don’t smoke at work why should I not have a right to work. the feds fund all law enforcement.

  3. Anonymous on

    i call bullshit. i RARELY drink when i smoke up its not a common thing and people that do drink and smoke weed then drive are just asking for trouble but for me, and you can ask my dad this too, because he hasnt ever noticed, i drive just the same if not better when im high. and i dont slow down on purpose to consciously compensate for it, its because going the normal speed i do when im high seems too fast. and that so called lateral travel is within the same lane not like when your drunk and swerving all over the place. and so friggin what if they cant answer math problems when theyr driving who the hell does that anyway?? you get zoned in on one thing yes and whats that one thing? drive and dont crash, i notice WAY more details when im driving high, because im worried i wont see something and crash, maybe thats just me, but the people that just get careless and dont dont pay attention, its not because of the weed (although that brings it out in more people) its because theyr just generally not good drivers and they cant admit it

  4. Tyler on

    I don’t know about you guys but when i drive stoned i slow down and pay more attention to everything like everyone has said. The bad thing is when i drive hella stoned out of town in the dark because i can’t see that great in darkness. But overall marijuana makes me drive more cautiously. I just wouldn’t suggest driving when you are really baked or really burnt out if so,splash some cold water onyourself lol

  5. Anonymous on

    Experienced smokers will know how to drive safely, whereas experienced drinkers get too overconfident and that is where accidents occur

  6. David762 on

    Drivers under the influence of alcohol will blow right through a stop-sign.
    Drivers under the influence of cannabis will not only stop at the stop-sign, they will patiently wait until the stop-sign changes to green.

    The USA government ~is lying|has always lied~ about driving while high. It is an even bigger fabrication for the Obama government to state that they are ending the War on Drugs, while introducing Federal drug DUI enforcement based upon a fraudulent test that cannot detect the extent of a driver’s incapacity, only whether that driver smoked cannabis sometime in the last 30 to 60 days. Welcome to the Police State.

  7. Anonymous on

    You always hear the “driving while high” argument when someone argues against cannabis being legal. Of course there are no studies to support this position.

    I would like to see a study where a person having used cannabis is compared with someone trying to drive using a cell phone.

  8. ray christl THC Ministry Cambodia on

    Anonymous Nation is despised by BUSH-NIXON-DEA that ARE coming for your little closet of fear.They feed on fear.You are the most weak people with the most liberal (previous)govt.and sensible sentencing code.Where is the courage you expect the Burmese to overthrow despotism,yet you have anonymous smoke-ins behind the CELEBRITY of MARC. Work on a countrywide REFERENDUM,and love the enemy like THOMAS JAMES *HEMP*Super teacher for the HARPER perverts of christ love.

  9. David762 on

    In fact, the Shafer Commission Report of 1972 also confirmed this data. President RM Nixon shelved this study, which recommended decriminalizing or re-legalizing marijuana, and began the War OF Drugs against those “dirty hippies” that were protesting his illegal war in Cambodia, and immoral war in Vietnam.

    Here’s a little secret that pops out of the Shafer Report when drilling down through their studies: re-legalizing marijuana would result in an increase in the number of marijuana users, and a decrease in the number of alcohol users. Over the course of the past 47 years of the War OF Drugs, how many lives could have been saved on America’s highways — thousands? many, many thousands?

    Marijuana is a reverse “gateway drug” !!

  10. Anonymous on

    I recall seeing a study back in 2003 about marijuana having little effect on driving and was absolutely shocked. Even more so to find out that it can enhance your attention and everything the above poster stated. I read that article years before I started driving and I learned how to drive stoned. The only few fender benders I’ve ever been in were one I hadn’t smoked weed since the day before. Where can I sign up to be a test subject?

    But seriously, the study in 2004 is hogwash. I will say that I never smoke while driving, and will usually wait at least 10 minutes to half hour before driving after smoking depending on how high I am. Its not like booze where you think you can drive after a sick pack, if you are too stoned to drive you won’t drive, but you’ll be mellow and driving safe in no time.

    I’m a Canadian, and I am a better driver stoned.

  11. Anonymous on

    I’ve noticed that: years ago, after some lovely strong Kush, I noticed that the only problem with driving was that my eyes were too dry to stay open with contact lenses in them! I did the speed limit and watched everyone else speed by like they normally do here (‘out of hell’).

    NORML warns of pot use & driving, but it’s one of these things whereby once the user is familiar with the effects and informed enough, operating heavy machinery is fine (obviously if you’re passing a joint, or anything else, you’re more likely to crash… also, too much hash can make one pass out for a few seconds, so I wouldn’t take ten hits of strong hash and hold each one for as long as possible while driving, or eat ten pineapples while driving).

  12. Anonymous on

    The intense perception during being high while driving is an advantage. It should be considered an alert and aware concept because ‘distraction’ is only an excuse necessary to know that drivers are paying attention to what is around them, and enjoying their ride. “”””Road rage”””” is another good issue to address for driving while high, more drivers will relax and not rush in the rat race, the flow of the traffic just works properly. Anxiety while driving is reduced. The senses are heightened so the driver feels the road down to its little bumps to its smooth overpass’ and anticipates everything in the careful manner of adding the patience to their trip. It really helps, being overcautious at times is alright and you can consider choices in slow motion if you’re blasted. It doesn’t matter, people who drive well can be high and people who don’t drive well will never drive proper whatever they’re on. Driving on coffee is a little anxious, a slight nervous effect from caffeine. Its probably worse for someone to drive after eating a feast than driving high!!… And Booze, well, the ones who drive perfect while high are the ones who don’t even drink liquor. Being distracted just means you react quicker and aren’t a zombie.