From the Guidelines
Marijuana use significantly impairs driving ability and should be avoided before operating a vehicle, as it increases the risk of motor vehicle accidents by more than two times, according to a meta-analysis of nine epidemiologic studies 1.
Key Points to Consider
- Cannabis users are at a higher risk of motor vehicle accidents, with drivers who test positive for cannabis or self-report using cannabis being more than twice as likely to be involved in motor vehicle crashes 1.
- The risk of fatal motor vehicle accidents co-involving alcohol is increased with higher blood levels of cannabis 1.
- THC (tetrahydrocannabinol) affects coordination, reaction time, and judgment, impairing critical driving skills such as attention span, reaction times, and the ability to track moving objects and maintain proper lane position.
- Unlike alcohol, there is no established "safe" blood concentration level for marijuana, and combining it with even small amounts of alcohol dramatically increases impairment.
Recommendations
- Do not drive for at least 4-6 hours after smoking marijuana and at least 8-12 hours after consuming edibles.
- Arrange alternative transportation if you've used marijuana, such as a designated driver, taxi, or rideshare service.
- The safest approach is complete separation of marijuana use and driving, as THC can remain detectable in your system for days or weeks, though the most severe impairment occurs within the first few hours after use.
Important Considerations
- Clinicians should discuss the risks of driving under the influence of cannabis with adults using cannabis and/or cannabinoids, especially those with cancer 1.
- Regular marijuana use can lead to long-term psychiatric risks, including an increased risk for developing depressive disorders and exacerbating psychiatric disorders in vulnerable individuals 1.
From the Research
Marijuana Use and Driving
- Marijuana use before or while driving significantly contributes to driving impairment and elevated risk of motor vehicle accidents, as found in a study published in the Journal of studies on alcohol and drugs 2.
- The prevalence of driving after using marijuana was high among adolescent marijuana users, with nearly half of all marijuana users reporting driving after use during the past 30 days, according to a study in Traffic injury prevention 3.
- As more states in the U.S legalize recreational and medicinal cannabis, rates of driving under the influence of this drug are increasing significantly, highlighting the need for enhanced surveillance, prevention, and control measures 4.
Risk Factors and Behaviors
- Perceived driving-related peer norms and perceived dangerousness of driving after smoking marijuana were associated with lower frequency of driving after smoking marijuana and smoking marijuana while driving, as found in a study published in the Journal of studies on alcohol and drugs 2.
- Heavy marijuana users were more likely to drive after using marijuana, and a higher prevalence of driving after drinking alcohol was also found among those who had driven after using marijuana, according to a study in Traffic injury prevention 3.
- Cannabis-impaired driving patterns were compared to alcohol-impaired driving patterns, highlighting the need for further research on detection procedures and the use of blood THC levels to gauge impairment 4.
Health Consequences
- Cannabis use has been linked to substantial adverse cardiovascular events, including myocardial infarction, cerebrovascular accidents, arrhythmia, and heart failure, as discussed in a review published in Nature reviews. Cardiology 5.
- Individuals with emergency department visits or hospitalizations due to cannabis were at increased risk of a new dementia diagnosis compared to those with all-cause hospital-based care or the general population, according to a study published in JAMA neurology 6.