Systematically Testing the Evidence on Marijuana

Cannabis and Driving Impairment

Quick Links:  Overview  | Download the Brief  |  References

Cannabis and Driving Impairment

By: Brittney A. Hultgren, PhD, Jason R. Kilmer, PhD, Thomas O. Walton, PhD, MSW, Michael S. Gilson, PhD, JD, and Joseph Lambuth, BS

Background: Driving after using cannabis products can be misperceived as “safe.” This misperception partially stems from comparing alcohol impairment to cannabis impairment, perceptions that compensatory driving behaviors (e.g., driving slower) while under the influence of cannabis leads to safer driving, and previous mixed findings in research. However, driving after using cannabis products may increase the chance of a crash.

Evidence Highlights:

  • While earlier research provided mixed findings on whether cannabis use impairs driving ability, several newer meta-analyses provide stronger evidence that cannabis impairs driving-related skills including increasing reaction time (i.e., taking longer to react), and decreasing attention and lateral control (i.e., lane weaving).1-3 Further, recent research suggests cannabis impairment reduces visual acuity which in turn reduces driving skills.4
  • Drivers under the influence of cannabis may engage in compensatory driving behaviors, (i.e., behaviors intended to help them counteract their impairment) such as driving slower, but these compensatory behaviors are more difficult when tasks are complex and therefore may not reduce the risk of crash or receiving a ticket.5-8
  • While higher levels of alcohol will affect driving to a greater extent than cannabis,9 cannabis impairment still may increase the risk of a crash.10-13 Driving under the influence of both alcohol and cannabis is especially dangerous as research suggest driving skills may be more negatively impacted than when using alcohol or cannabis alone.3,5,7,14
  • There is some variability in the research on how long an individual should wait to drive after using cannabis products. While some research suggested the effects of cannabis are reduced starting at 4.5 hours15, other research and meta-analyses suggests almost all effects are recovered between 5-7 hours after inhalation.2, 16 However, given the differences in potency and modes of use, current guidelines suggest waiting 6-8 hours after inhalation and 8-12 hours after oral ingestion.16 Different modes of use (e.g., smoking, edibles, dabbing) can change the time to onset and length of impairment.15
  • Mild residual impairment in episodic and working memory, processing speed, and executive functioning can persist for days following cannabis abstinence.17 These effects can reduce driving skills and may be why some research has found increases in crashes among those who use cannabis more generally, even when they were not acutely impaired.
  • Cannabidiol (CBD) by itself does not appear to affect driving ability.18 However, contrary to the belief of some, there is no evidence that CBD reliably protects against THC-induced driving impairments.19,20
  • Tolerance is important to consider. Several studies suggest that driving impairment is worse among those who use cannabis infrequently, compared to those who use more frequently.2,5,16 However, these individuals may also be using cannabis products in ways that increase their overall THC levels (e.g., using more or higher potency products to combat tolerance).16 Additionally, compared to those who use cannabis less frequently, they may be less aware of their impairment and report higher levels of confidence in their driving.21 Thus, in real-life scenarios those with a higher tolerance to cannabis may not be any safer to drive after using cannabis than those without tolerance.
  • Research on how synthetic cannabinoids (e.g., Delta-8, Delta-10, Spice, K2) may impact driving is limited and consists primarily of case studies and experimental research on psychomotor effects.22-25 However, the available research suggests that synthetic cannabinoids are typically more potent than THC,26 and therefore can impair driving at least as much as THC products.

Clinical Considerations:

  • Just as states differ on legal status of cannabis, states also differ on cannabis impaired driving laws. Some states have per se laws, where the presence of a certain amount of THC or its derivatives (e.g., 5 ng/mL in blood) constitutes impairment. Others have zero tolerance laws where any amount is considered impairment. Key factors to consider with patients include:
    • THC and its derivatives can last in the blood stream longer for people who use cannabis more frequently and more heavily.27 Therefore, they may have THC in their blood without feeling acutely impaired.
    • While consumers can readily purchase Blood Alcohol Content (BAC) breathalyzers, comparable products to detect level of cannabis-induced impairment do not currently exist.
  • Increasingly, many available cannabis products have high percentages of THC,28 which may increase the likelihood of driving impairment.

Q&A:

  • What to do if you think someone is acutely impaired by cannabis and they drove to your clinic?
    • First, it is important to not make assumptions – red eyes could mean allergies, odor could mean they were with someone who was using cannabis. Next, ask when they last used cannabis.
      • If the patient states they used recently and they drove to your clinic, it is important to first know your own office’s policy on impaired patients in case there is something you are required or mandated to do.
      • Next, discuss options for safe transportation or a space for waiting. 
  • What you could hear a patient say about cannabis use and driving and how you could respond.
    • “I drive better after smoking weed.”
      • You could respond: “Some people report they drive better after using cannabis because cannabis reduces their anxiety. However, there is no research to support that driving improves after cannabis use. Many people do report driving slower after using cannabis and this could be why you might feel you drive better. However, even if you drive slower, other factors such as your ability to react quickly to other drivers, and your ability to stay in your lane, are impacted by cannabis and can increase your chances of a crash or getting pulled over.”
    • “I drank too much and needed to sober up, so I smoked weed.”
      • You could respond: “Research shows that driving after using both alcohol and cannabis together may be more dangerous than using either one alone because of the drug interaction introduced when both substances are used. What are some other things you think you can do instead if you feel you drank too much to drive in the future?”
    • “Driving after smoking weed is safer than drinking.”
      • You could respond: “Yes, drinking alcohol at higher amounts could impact your ability to drive more than cannabis might. However, driving after using cannabis is still unsafe. Using cannabis is likely to feel different than using alcohol, which makes sense since they are different substances. However, it is important to know they both can impair your ability to drive.”
    • “It is legal here, so I can use cannabis and drive legally.”
      • You could respond: “You’re right that using cannabis is legal here, but driving impaired by cannabis is not. In fact, in some states driving after using cannabis is not legal.” Next, you can discuss your state’s impaired driving laws. If your state has a zero tolerance or per se law, you may consider discussing the implications of having THC in their blood without impairment.
    • “Right after smoking, my driving might be impaired, but I’m fine after about an hour and a half.”
      • You could respond: “That’s a pretty common belief, and research does show that folks perceive their own cannabis-related impairment goes away about 90 minutes after smoking. However, when researchers tested their driving ability, they continued to find impairment in driving despite most participants feeling confident in their ability to drive.” 16
    • “How long should I wait to drive after using cannabis?”
      • You could respond: “The time you should wait depends on several factors including how much cannabis you use and how you use it. I suggest you wait at least5-6 hours, however it will be safer, and the current low-risk guidelines suggest waiting 6-8 hours after inhaling, such as smoking and vaping, and 8-12 hours for ingestion, or eating or drinking. How do these times map on to how long you typically wait to drive?”

Bottom Line:

Cannabis use can impair driving and driving after cannabis use is associated with elevated risk of a crash. Unlike alcohol, there is no ready way to calculate whether an individual is still impaired following recent cannabis use. Clinicians should be aware of the misperceptions regarding the safety of driving after cannabis use and advise patients who report using cannabis to avoid driving after use. While ranges can vary based on mode of use, potency, and amount used, patients could be encouraged to wait at least 4.5-6 hours, preferably 6-8 hours, before driving after inhaling, and 8-12 hours before driving after oral ingestion. 

Suggested Citation: Hultgren BA, Kilmer JR, Walton TO, Gilson MS, Lambuth J. Cannabis and Driving Impairment. The Systematically Testing the Evidence on Marijuana Project; February 2025. Accessed (Month DD, YYYY). https://www.cannabisevidence.org/clinician-resources/clinician-briefs/cannabis-and-driving-impairment/ 

Acknowledgements: Thank you to Esther Choo, MD MPH and Thomas D. Marcotte, PhD for critically reviewing this document. 

Author Affiliations: All authors are affiliated with the University of Washington. 

Disclosure of Potential Conflicts of Interest: All authors have no conflicts of interest to declare.

Download the Brief

Download Report

STEM Chronic Pain Brief

References

  1. Alvarez L, Colonna R, Kim S, Chen C, Chippure K, Grewal J, Kimm C, Randell T, & Leung V. Young and under the influence: A systematic literature review of the impact of cannabis on the driving performance of youth. Accid Anal Prev. 2021;151. Accessed Oct 23, 2024. https://doi.org/10.1016/j.aap.2020.105961
  2. McCartney D, Arkell TR, Irwin C, & McGregor IS. Determining the magnitude and duration of acute Δ9-tetrahydrocannabinol (Δ9-THC)-induced driving and cognitive impairment: A systematic and meta-analytic review. Neurosci Biobehav Rev. 2021;126:175–193. Accessed Oct 23, 2024. https://doi.org/10.1016/j.neubiorev.2021.01.003
  3. Simmons SM, Caird JK, Sterzer F, & Asbridge M. The effects of cannabis and alcohol on driving performance and driver behaviour: A systematic review and meta‐analysis. Addiction. 2022;117(7):1843–1856. Accessed Oct 23, 2024. https://doi.org/10.1111/add.15770
  4. Ortiz-Peregrina S, Ortiz C, Castro-Torres JJ, Jiménez JR, & Anera RG. Effects of Smoking Cannabis on Visual Function and Driving Performance. A Driving-Simulator Based Study. Int J Environ Res Public Health. 2020;17(23):9033. Accessed Oct 23, 2024. https://doi.org/10.3390/ijerph17239033
  5. Hartman RL & Huestis MA. Cannabis Effects on Driving Skills. Clin Chem. 2013;59(3):478–492. Accessed Oct 23, 2024. https://doi.org/10.1373/clinchem.2012.194381
  6. Ronen A, Gershon P, Drobiner H, Rabinovich A, Bar-Hamburger R, Mechoulam R, Cassuto Y, & Shinar D. Effects of THC on driving performance, physiological state and subjective feelings relative to alcohol. Accid Anal Prev. 2008;40(3): 926-934. Accessed Feb 14, 2025. https://doi.org/10.1016/j.aap.2007.10.011
  7. Ronen A, Chassidim HS, Gershon P, Parmet Y, Rabinovich A, Bar-Hamburger R, Cassuto Y, & Shinar D. The effect of alcohol, THC and their combination on perceived effects, willingness to drive and performance of driving and non-driving tasks. Accid Anal Prev. 2010;42(6):1855-1865. Accessed Feb 14, 2025. https://doi.org/10.1016/j.aap.2010.05.006
  8. 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. Accessed Feb 14, 2025. https://doi.org/10.1016/j.aap.2009.04.021
  9. White MA & Burns NR. The risk of being culpable for or involved in a road crash after using cannabis: A systematic review and meta-analyses. Drug Sci Policy Law. 2021;7. Accessed Oct 24, https://doi.org/10.1177/20503245211055381
  10. Brubacher JR, Chan H, Erdelyi S, Macdonald S, Asbridge M, Mann RE, Eppler J, Lund A, MacPherson A, Martz W, Schreiber WE, Brant R, & Purssell RA. Cannabis use as a risk factor for causing motor vehicle crashes: a prospective study. Addiction. 2019;114(9):1616-1626. Accessed Oct 24, https://doi.org/10.1111/add.14663
  11. Rogeberg O & Elvik R. The effects of cannabis intoxication on motor vehicle collision revisited and revised. Addiction. 2016;111(8):1348-1359. Accessed Feb 14, 2025. https://doi.org/10.1111/add.13347
  12. Li M, Brady JE, DiMaggio CJ, Lusardi AR, Tzong KY, & Li G. Marijuana Use and Motor Vehicle Crashes. Epidemiol Rev. 2011;34(1):65–72. Accessed Feb 14, 2025. https://doi.org/10.1093/epirev/mxr017
  13. 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:e Accessed Feb 14, 2025. https://doi.org/10.1136/sbmj.e1735
  14. Fares A, Wickens CM, Mann RE, Di Ciano P, Wright M, Matheson J, Hasan OSM, Rehm J, George TP, Samokhvalov AV, Shuper PA, Huestis MA, Stoduto G, Brown T, Stefan C, Rubin-Kahana DS, Le Foll B, & Brands B. Combined effect of alcohol and cannabis on simulated driving. Psychopharmacol. 2021;239(5):1263-1277. Accessed Feb 14, 2025. https://doi.org/10.1007/s00213-021-05773-3
  15. Marcotte TD, Umlauf A, Grelotti DJ, Sones EG, Sobolesky PM, Smith BE, Hoffman MA, Hubbard JA, Severson J, Huestis MA, Grant I, & Fitzgerald RL. Driving Performance and Cannabis Users’ Perception of Safety: A Randomized Clinical Trial. JAMA. 2022;79(3):201. Accessed Oct 23, 2024. https://doi.org/10.1001/jamapsychiatry.2021.4037
  16. Fischer B, Robinson T, Bullen C, Curran V, Jutras-Aswad D, Medina-Mora ME, Pacula RL, Rehm J, Room R, van den Brink W, & Hall W. Lower-Risk Cannabis Use Guidelines (LRCUG) for reducing health harms from non-medical cannabis use: A comprehensive evidence and recommendations update. Int J Drug Policy. 2022;99. Accessed Oct 24, 2024. https://doi.org/10.1016/j.drugpo.2021.103381
  17. Schreiner AM, & Dunn ME. Residual effects of cannabis use on neurocognitive performance after prolonged abstinence: a meta-analysis. Exp Clin Psychopharmacol. 2012;20(5):420-429. Accessed Oct 21, 2024. https://doi.org/1037/a0029117
  18. McCartney D, Suraev AS, Doohan PT, Irwin C, Kevin RC, Grunstein RR, Hoyos CM, McGregor IS. Effects of cannabidiol on simulated driving and cognitive performance: a dose-ranging randomised controlled trial. J Psychopharmacol. 2022;36(12):1338-1349. Accessed Nov 6, 2024. https://doi.org/10.1177/02698811221095356
  19. Arkell TR, Lintzeris N, Kevin RC, Ramaekers JG, Vandrey R, Irwin C, Haber PS, & McGregor IS. Cannabidiol (CBD) content in vaporized cannabis does not prevent tetrahydrocannabinol (THC)-induced impairment of driving and cognition. Psychopharmacology. 2019;236:2713-2724. Accessed Oct 24, 2024. https://doi.org/1007/s00213-019-05246-8
  20. Rubin R. Driving under the influence of CBD or THC—is there a difference? JAMA. 2020;324(21):2144-2145. Accessed Oct 24, 2024. https://doi.org/10.1001/jama.2020.22181
  21. Brooks-Russell A, Brown T, Friedman K, Wrobel J, Schwarz J, Dooley G, Ryall KA, Steinhart B, Amioka E, Milavetz G, Wang GS, & Kosnett MJ. Simulated driving performance among daily and occasional cannabis users. Accid Anal Prev. 2021;160. Accessed Feb 14, 2025. https://doi.org/10.1016/j.aap.2021.106326
  22. Orazietti V, Basile G, Giorgetti R, & Giorgetti A. Effects of synthetic cannabinoids on psychomotor, sensory and cognitive functions relevant for safe driving. Front Psychiatry. 2022;13. Accessed Feb 14, 2025. https://doi.org/10.3389/fpsyt.2022.998828
  23. McCain KR, Jones JO, Chilbert KT, Patton AL, James LP, & Moran JH. Impaired driving associated with the synthetic cannabinoid 5F-ADB. JFSC. 2018;6(1):105. Accessed Feb 14, 2025. https://doi.org/10.15744/2348-9804.6.105
  24. Musshoff F, Madea B, Kernbach-Wighton G, Bicker W, Kneisel S, Hutter M, & Auwärter V. Driving under the influence of synthetic cannabinoids (“Spice”): a case series. Int J Legal Med. 2014;128(1):59–64. Accessed Feb 14, 2025. https://doi.org/10.1007/s00414-013-0864-1
  25. Yeakel JK & Logan BK. Blood synthetic cannabinoid concentrations in cases of suspected impaired driving. J Anal Toxicol. 2013;37(8):547-551. Accessed Feb 14, 2025. https://doi.org/10.1093/jat/bkt065
  26. Alves VL, Gonçalves JL, Aguiar J, Teixeira HM, & Câmara JS. The synthetic cannabinoids phenomenon: from structure to toxicological properties. A review. Crit Rev Toxicol. 2020;50(5):359-382. Accessed Feb 14, 2025. https://doi.org/10.1080/10408444.2020.1762539
  27. Sharma P, Murthy P, & Bharath MM. Chemistry, metabolism, and toxicology of cannabis: clinical implications. Iran J Psychiatry. 2012;7(4):149-156. Accessed Oct 24, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC3570572/
  28. ElSohly MA, Chandra S, Radwan M, Majumdar CG, & Church JC. A comprehensive review of cannabis potency in the United States in the last decade. BP:CNNI. 2021;6(6):603-606. Accessed Oct 24, 2024. https://doi.org/1016/j.bpsc.2020.12.016