From the Guidelines
Marijuana users should never drive after using the substance, as it significantly increases the risk of motor vehicle accidents, with drivers who test positive for cannabis being more than twice as likely to be involved in crashes 1.
Key Points to Consider
- The risk of motor vehicle accidents increases substantially when marijuana is combined with alcohol or other drugs, with higher blood levels of cannabis associated with an increased risk of fatal motor vehicle accidents co-involving alcohol 1.
- The effects of marijuana can last for several hours after use, and THC can be detectable in the body for days or even weeks afterward, making it difficult to determine when it is safe to drive.
- Unlike alcohol, there is no established legal limit or reliable roadside test for marijuana impairment, and many states have "per se" laws that make it illegal to drive with any detectable amount of THC in the system, regardless of actual impairment.
Recommendations for Safe Driving
- Individuals should wait at least 6-8 hours after smoking marijuana before driving, and longer (at least 8-12 hours) after consuming edibles, as their effects last longer and can be more unpredictable.
- The safest approach is to completely separate marijuana use from driving by using public transportation, ride-sharing services, or having a designated driver who has not consumed any substances.
- Clinicians should discuss the risks of driving under the influence of marijuana with adults using cannabis and/or cannabinoids, and emphasize the importance of prioritizing safety on the roads 1.
From the Research
Marijuana Use and Driving
- Marijuana use can impair driving ability and increase the risk of motor vehicle accidents 2, 3, 4, 5
- Studies have shown that driving after marijuana use is a common behavior among users, with nearly half of adolescent marijuana users reporting driving after use in the past 30 days 4
- Frequent marijuana users are more likely to drive after use and report waiting less time before driving after cannabis use 5
- The perceived impact of cannabis on driving ability is not always associated with wait time before driving, suggesting that other factors may influence driving behavior after marijuana use 5
Risk Factors for Driving After Marijuana Use
- Perceived driving-related peer norms and perceived dangerousness of driving after marijuana use are associated with decreased frequency of driving after smoking marijuana and smoking marijuana while driving 3
- Age of marijuana initiation and patterns of use are also related to driving after marijuana use, with heavy users more likely to engage in this behavior 4
- Cannabis use frequency is a predictor of self-reported impact of cannabis on driving ability and wait time before driving, with more frequent users reporting less impairment and waiting less time before driving 5
Implications for Public Health
- The legalization of cannabis for medical and recreational purposes has increased its use and availability, highlighting the need for enhanced surveillance, prevention, and control measures to mitigate the negative impacts of marijuana consumption and related behaviors 2, 4, 6
- Further research is needed to address gaps in knowledge on cannabis pharmacology and the endocannabinoid system, particularly with regard to the enduring consequences of exposure during critical windows of brain development or for consumption of large daily doses of cannabis with high content Δ 9-tetrahydrocannabinol 6