What You Need to Know About Marijuana Use and Driving

Fast Facts

The number of self-reported marijuana users is increasing. In 2014, there were 7,000 new users of marijuana per day.4

13% of nighttime, weekend drivers have marijuana in their system; this is up from 9% in 2007.5

After alcohol, marijuana is the drug most often linked to drugged driving.6

Because driving is such a common activity, it’s easy to forget how you really must stay alert to stay safe. While it may seem like your body goes on automatic when accelerating or changing lanes, your brain is actually in high gear.
Drugs and alcohol interfere with the brain’s ability to function properly. Tetrahydrocannabinol (THC), which is the main active ingredient in marijuana, affects areas of the brain that control your body’s movements, balance, coordination, memory, and judgment.1-3

How does marijuana affect driving?

Driving while impaired by any substance, including marijuana, is dangerous. Marijuana, like alcohol, negatively affects a number of skills required for safe driving:

Marijuana can slow your reaction time and ability to make decisions.1-3, 7-9
Marijuana use can impair coordination, distort perception, and lead to memory loss and difficulty in problem-solving.1-3, 7-9
The risk of impaired driving associated with marijuana in combination with alcohol appears to be greater than that for either by itself.2, 9

What do we know about marijuana use and the risk of car crashes?

Although we know marijuana negatively affects a number of skills needed for safe driving, and some studies have shown an association between marijuana use and car crashes, it is unclear whether marijuana use actually increases the risk of car crashes. This is because:

An accurate roadside test for drug levels in the body doesn’t exist.
Marijuana can remain in a user’s system for days or weeks after last use (depending on how much a person uses and how often they use marijuana).
Drivers are not always tested for drug use, especially if they have an illegal blood alcohol concentration level because that is enough evidence for a driving-while-impaired charge.
When tested for substance use following a crash, drivers can have both drugs and alcohol or multiple drugs in their system, making it hard to know which substance contributed more to the crash.

Is there a legal limit for marijuana impairment while operating a vehicle?

Laws vary from state to state. If you intend to drive, the safest option is not to have any alcohol or drugs in your system at all.

For more information, visit:

CDC’s Impaired Driving: Get the Facts: http://www.cdc.gov/motorvehiclesafety/impaired_driving/impaired-drv_factsheet.html

Drug Facts: Drugged Driving: https://www.drugabuse.gov/publications/drugfacts/drugged-driving

Cannabis: http://www.samhsa.gov/atod/cannabis

National Highway Traffic Safety Administration Impaired Driving Fact Sheet: http://www.nhtsa.gov/Impaired

References

Lenné MG, Dietze PM, Triggs TJ, Walmsley S, Murphy B, Redman JR. The effects of cannabis and alcohol on simulated arterial driving: Influences of driving experience and task demand. Accid Anal Prev. 2010;42(3):859-866. doi:10.1016/j.aap.2009.04.021.
Hartman RL, Huestis MA. Cannabis effects on driving skills. Clin Chem. 2013;59(3):478-492. doi:10.1373/clinchem.2012.194381.
Hartman RL, Brown TL, Milavetz G, et al. Cannabis effects on driving lateral control
with and without alcohol. Drug Alcohol Depend. 2015;154:25-37. doi:10.1016/j. drugalcdep.2015.06.015.
Azofeifa A, Mattson ME, Schauer G, McAfee T, Grant A, Lyerla R. National Estimates of Marijuana Use and Related Indicators — National Survey on Drug Use and Health, United States, 2002–2014. MMWR Surveill Summ 2016;65(No. SS-11):1–25. DOI: http://dx.doi. org/10.15585/mmwr.ss6511a1HYPERLINK “https://www.cdc.gov/Other/disclaimer.html”.
Berning, A., Compton, R., Wochinger, K., Results of the 2013–2014 National Roadside Survey of alcohol and drug use by drivers. 2015, National Highway Traffic Safety Administration: Washington, DC. (DOT HS 812 118).
Center for Behavioral Health Statistics and Quality (CBHSQ). Behavioral Health Trends
in the United States: Results from the 2014 National Survey on Drug Use and Health. Rockville, MD: Substance Abuse and Mental Health Services Administration; 2015. HHS Publication No. SMA 15-4927, NSDUH Series H-50.
Lenné MG, Dietze PM, Triggs TJ, Walmsley S, Murphy B, Redman JR. The effects of cannabis and alcohol on simulated arterial driving: Influences of driving experience and task demand. Accid Anal Prev. 2010;42(3):859-866. doi:10.1016/j.aap.2009.04.021.
Hartman RL, Huestis MA. Cannabis effects on driving skills.Clin Chem. 2013;59(3):478-492. doi:10.1373/clinchem.2012.194381.
Hartman RL, Brown TL, Milavetz G, et al. Cannabis effects on driving lateral control
with and without alcohol. Drug Alcohol Depend. 2015;154:25-37. doi:10.1016/j. drugalcdep.2015.06.015.