Addiction Drug Use Marijuana How Does Marijuana Affect Driving? Chance of Crashing Increases If You Choose to Drive High By Buddy T Buddy T Facebook Twitter Buddy T is an anonymous writer and founding member of the Online Al-Anon Outreach Committee with decades of experience writing about alcoholism. Learn about our editorial process Updated on October 04, 2020 Medically reviewed Verywell Mind articles are reviewed by board-certified physicians and mental healthcare professionals. Medical Reviewers confirm the content is thorough and accurate, reflecting the latest evidence-based research. Content is reviewed before publication and upon substantial updates. Learn more. by Steven Gans, MD Medically reviewed by Steven Gans, MD Steven Gans, MD is board-certified in psychiatry and is an active supervisor, teacher, and mentor at Massachusetts General Hospital. Learn about our Medical Review Board Print Alexandra Draghici/Getty Images Table of Contents View All Table of Contents Chances of Crashing Higher Levels, Higher Risks Driving While Stoned Problems With These Studies Risks Do Remain Using marijuana can impair your judgment, motor coordination, ability to concentrate, and slow your reaction time. Therefore, it can impair your driving skills. Anytime the skills needed to drive safely are impaired, even slightly, the chances of having an auto crash increase. Specifically, studies have found that marijuana use affects the driver's concentration and ability to perceive time and distance. This may lead to poor speed control, drowsiness, distraction, and the inability to read road signs accurately. The Chances of Crashing Increases More than one research study has found a direct link between THC (the psychoactive chemical in marijuana) concentration in the blood and impaired driving skills. An analysis of several studies has found that the risk of being involved in a motor vehicle crash significantly increases after using marijuana. Another meta-analysis estimates that the risk of a crash that results in serious injury or death doubles after marijuana use. In the 2015 "Traffic Safety Facts: Drug and Alcohol Crash Risk" report, the National Highway Traffic Safety Administration (NHTSA) notes that THC increased crash risk by 1 to 3 times more than sober drivers. Some studies also note that high-risk groups for car accidents are those most likely to use marijuana. Most notably, this is young men in their late teens and 20s. This could play a factor in some of the statistics as well. Teen Marijuana Use by the Numbers Higher Levels, Higher Risks When drivers are involved in auto crashes, the drivers with THC in their blood are more likely to be the driver responsible for the accidents. This is compared to drivers who were not using drugs or alcohol. It is particularly true when THC is found at higher levels. When marijuana use is combined with alcohol, the risk of having a highway mishap is significantly greater — much greater than with either drug used by itself. With the two combined their effect on driving skills are not added, they are multiplied, research shows. Driving While Stoned Common Research from the NHTSA indicates that when drivers are killed in motor vehicle crashes, drugs and alcohol are involved about 11% of the time. The NHTSA report also shows an increase in the number of drivers who have tested positive for marijuana. They state that one in four drivers tested had THC in their system. Increases in driving while under the influence of marijuana is attributed to the recent legalization and popularization of medical and recreational cannabis in many U.S. states. Some drivers who use marijuana claim that smoking weed actually improves their concentration and therefore, their driving skills. Researchers have concluded that this might be true for the first few minutes of driving. However, marijuana users can soon become weary, bored, or distracted and their attention can begin to drift. Problems With These Studies The NHTSA, CDC, and almost every researcher that studies this issue notes that there are concerns with the marijuana-impaired driving statistics. One glaring problem is the testing procedures because THC can be detected in a person's system for days or weeks at a time. Unlike roadside tests for blood alcohol content, the tests currently used for marijuana can pick up traces even if the person is not impaired at the time of a crash. They may have smoked the day before or even earlier and the tests will still be positive. The CDC notes that multiple drugs in a person's system make it difficult to determine which contributed to a crash. Also, drivers are not always tested for drugs, particularly if they already have an illegal blood alcohol concentration level. All of these factors can throw off data used in scientific studies. The Risks Do Remain Despite these concerns, the research does show that marijuana impairs a person's ability to drive. Also, though the laws vary by state, it is illegal to drive impaired in the United States. Using marijuana and driving while impaired can have serious legal consequences. As a conclusion, the CDC says that "the safest option is not to have any alcohol or drugs in your system at all." DUI Laws by State 5 Sources Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Rogeberg O, Elvik R. The effects of cannabis intoxication on motor vehicle collision revisited and revised. Addiction. 2016;111(8):1348-59. doi: 10.1111/add.13347 Asbridge M, Hayden JA, Cartwright JL. Acute cannabis consumption and motor vehicle collision risk: systematic review of observational studies and meta-analysis. BMJ. 2012;344:e536. doi:10.1136/bmj.e536 Compton RP, Berning A. Drug and alcohol crash risk. (Traffic Safety Facts Research Note. DOT HS 812 117). Washington, DC: National Highway Traffic Safety Administration. February 2015. Li MC, Brady JE, Dimaggio CJ, Lusardi AR, Tzong KY, Li G. Marijuana use and motor vehicle crashes. Epidemiol Rev. 2012;34:65-72. doi:10.1093/epirev/mxr017 Office of Noncommunicable Diseases, Injury, and Environmental Health. What You Need to Know About Marijuana Use and Driving. Centers for Disease Control and Prevention. 2017. Additional Reading Asbridge M, Hayden JA, Cartwright JL. Acute Cannabis Consumption and Motor Vehicle Collision Risk: Systematic Review of Observational Studies and Meta-Analysis.BMJ. 2012;344:e536 doi: http://dx.doi.org/10.1136/bmj.e536. Office of Noncommunicable Diseases, Injury, and Environmental Health. What You Need to Know About Marijuana Use and Driving. Centers for Disease Control and Prevention. 2017. Rogeberg O, Elvik R. The Effects of Cannabis Intoxication on Motor Vehicle Collision Revisited and Revised. Addiction. 2016;111:1348-59. doi: http://dx.doi.org/10.1111/add.13347. By Buddy T Buddy T is an anonymous writer and founding member of the Online Al-Anon Outreach Committee with decades of experience writing about alcoholism. See Our Editorial Process Meet Our Review Board Share Feedback Was this page helpful? Thanks for your feedback! What is your feedback? Other Helpful Report an Error Submit Get Treatment for Addiction Advertiser Disclosure × The offers that appear in this table are from partnerships from which Verywell Mind receives compensation.