By HealthDataConsortium.org Research Team
Research shows that cannabis can impair driving. Both the CDC and NHTSA focus on impairment, and neither page gives a safe waiting time after use. The CDC says it is difficult to connect the presence of cannabis or a THC concentration to impairment in any one person. If you intend to drive, the CDC says the safest option is not to use any alcohol or drugs, including cannabis. This guide explains what the evidence supports, where it stops, and how to plan a safer trip.
What Research Can Say About Cannabis and Driving
The Centers for Disease Control and Prevention (CDC) states that cannabis affects brain areas that control movement, balance, coordination, memory and judgment. It says cannabis can slow reaction time and decision-making, impair coordination and distort perception. The CDC also says studies have shown an association between acute cannabis use and car crashes, and that more research is needed. It adds that using multiple substances at the same time, such as cannabis and alcohol, can increase impairment.
The National Highway Traffic Safety Administration (NHTSA) reaches a similar position. It says research shows marijuana impairs motor skills, lane tracking and cognitive functions. It also says using two or more drugs at once, including alcohol, can amplify the impairing effects of each.
What Research Cannot Say
It cannot turn a THC level into a personal verdict
The CDC says it is difficult to connect the presence of cannabis, or the concentration of THC, to impairment in driving performance for an individual person. NHTSA adds that the presence of a drug in a driver's system does not necessarily mean the driver is impaired.
It cannot supply a waiting time
Neither the CDC page nor the NHTSA page gives a waiting period after which driving is safe, and this guide does not offer one. Given the CDC's statement about individual impairment, a single number for everyone is not something these sources support.
It cannot fully separate cannabis from other risk factors
NHTSA reports that its Drug and Alcohol Crash Risk Study found marijuana users are more likely to be involved in crashes. It also notes the increased risk may be due in part to marijuana users being more likely to be young men, who are generally at higher risk of crashes. The CDC and NHTSA both say more research is needed to understand the problem fully.
It cannot rely on your own judgment
NHTSA states that impaired drivers cannot accurately assess their own impairment, and that no one should drive after using any impairing substance.
A Research-Literacy Checklist for Driving Claims
These questions come from the limits the CDC and NHTSA describe. Use them on any headline, social post or product page that makes a claim about cannabis and driving.
- Does the claim measure impairment, or only whether a substance was present? NHTSA says presence alone does not necessarily mean impairment.
- Does it offer one waiting time or THC number that applies to everyone? The CDC says linking a THC concentration to an individual's driving impairment is difficult.
- Were other substances involved? Alcohol combined with cannabis can increase impairment, according to both agencies.
- Does it describe a group that differs from the general driving population? NHTSA cautions that age and sex differences may account for part of the crash-risk difference.
- Does it say cannabis cannot impair driving, or makes a driver safer? NHTSA calls these misconceptions and says several scientific studies indicate they are false.
- Does it help you plan? The CDC and NHTSA pages both end with planning steps, such as a sober driver or another ride.
Making a Safer Transport Decision
Both agencies recommend planning ahead of time.
- Choose not to drive, and remind friends and family to do the same.
- Assign a trusted designated driver who will not drink or use drugs.
- Arrange a ride home with someone who has not been using alcohol or drugs, or use a rideshare service or taxi.
- If you host, NHTSA says it is your job to make sure all guests leave with a sober driver.
- Read the warning label on any prescription or over-the-counter medicine. NHTSA notes that a warning against operating heavy machinery includes driving a vehicle.
Who Should Seek Professional Advice
- People who use cannabis for a health reason or take prescription medicines: ask your prescriber or pharmacist about driving.
- Anyone with a question about how impaired-driving laws apply to them: speak with a licensed attorney in your state. NHTSA states that driving impaired by any substance is against the law in all 50 states and the District of Columbia, including where marijuana laws have changed.
What This Guide Does Not Cover
This is a safety and research-literacy guide. It does not cover workplace drug testing, which is a separate question. For background on federal cannabis status, see our explainer on what rescheduling did not change. HealthDataConsortium.org is an independent analytical publication and does not provide medical or legal advice. See the Medical Disclaimer and our Methodology & Disclosures. More articles are in the Cannabis category.
Sources
- Centers for Disease Control and Prevention, “Cannabis and Driving,” page dated February 22, 2024, reviewed September 30, 2026: cdc.gov/cannabis/health-effects/driving.html
- National Highway Traffic Safety Administration, “Drug-Impaired Driving,” reviewed September 30, 2026: nhtsa.gov/risky-driving/drug-impaired-driving
