Drug and cannabis DUI laws by state: THC limits, testing and medicines
What state drug driving laws say about THC, drug testing and the medicines you take
Picture a driver who buys a cannabis vape at a licensed store, uses it at a friend’s home, waits an hour and feels clear. The purchase was legal. The drive home may not be. In some states, a blood test could support a charge even days later.
Every state bans drug impaired driving. But states differ on what a prosecutor must prove, which drugs count and how testing works. In a National Highway Traffic Safety Administration (NHTSA) study, active THC turned up in 25.1% of seriously or fatally injured road users. Alcohol turned up in 23.1% [3]. THC (tetrahydrocannabinol) is the main intoxicating compound in cannabis.
This guide covers the law types, where states stand, what drug tests show and how to check your state’s law. For the health side, see our guide to drug- and medication impaired driving.
Legal to buy is not legal to drive
NHTSA puts it plainly: driving impaired by any substance, legal or illegal, is against the law in every state and DC [2]. Legalization changes where adults may use cannabis, not the rules of the road.
The Insurance Institute for Highway Safety (IIHS) counts 24 states and DC that allow adult cannabis use at 21 and older, as of August 2026 [6]. Many more allow medical use, but none allow driving while impaired [6].
The same rule reaches other newly legal products. Colorado voters decriminalized personal use of certain psychedelics in 2022. The state’s transportation department still treats driving under their influence as a DUI and advises waiting at least 24 hours [15]. Minnesota’s vehicle rules name hemp derived THC edibles alongside cannabis [12].
Three ways states write drug driving laws
A traffic safety attorney reading a drug driving statute asks one question first: what must the state prove? The answers fall into a few groups.
Comparison compiled by Safety Behind the Wheel Foundation
Law types at a glance
| Law type | What the state must prove | Verified examples | What it means for you |
|---|---|---|---|
| Impairment based (“under the influence”) | A drug affected your ability to drive, shown by driving, behavior, tests and lab results | Available in every state [2] | No drug level is “safe” if you are impaired |
| Zero tolerance per se | Any detectable amount of a listed drug, sometimes including its by products (metabolites) | Arizona, Pennsylvania and Utah, for THC and its metabolites [1] | A test can reflect use from days earlier [7] |
| Numeric per se | A drug at or above a set level | Washington, Montana and Illinois at 5 ng/mL of THC; Ohio at 2 ng/mL [1, 5] | Being under the number does not prove you were fit to drive |
| Permissible inference | At or above a set level, a judge or jury may infer impairment, but you can rebut it | Colorado, at 5 ng/mL of THC [1, 6] | The number is evidence, not an automatic conviction |
ng/mL = nanograms per milliliter of blood. Sources: GHSA, laws reviewed June 2025 [1]; NCSL, March 2024 [5]; IIHS, August 2026 [6].
Per se is Latin for “by itself”: the test result alone proves the offense. Zero tolerance is the strictest version, because any measurable amount counts [1]. In the Governors Highway Safety Association (GHSA) review of June 2025, 16 states had zero tolerance laws and 5 had per se limits for 1 or more drugs [1]. Those states can still charge impairment too.
Where the states stand on cannabis
GHSA’s state table (laws reviewed June 2025) sorts cannabis specific driving laws as follows, grouped here in our own format [1]:
- Zero tolerance for THC and its metabolites: Arizona, Delaware, Georgia, Indiana, Oklahoma, Pennsylvania, Rhode Island, South Dakota and Utah.
- Zero tolerance for active THC only: Iowa, Michigan and Wisconsin (Wisconsin’s law names delta-9-THC). GHSA also lists Minnesota here. See below.
- Numeric THC limits: Illinois, Montana and Washington at 5 ng/mL; Ohio at 2 ng/mL; Nevada at 2 ng/mL, but only in felony cases.
- Permissible inference: Colorado at 5 ng/mL.
- Proof of impairment: the remaining 31 states and DC, by our count of the table.
The National Conference of State Legislatures (NCSL), as of March 2024, lists the same 5 numeric limit states and the same 12 zero tolerance states, without Minnesota [5].
Trackers sometimes disagree, which is why official sources matter. Minnesota’s 2025 statute leaves cannabis and THC out of its “any amount” drug rule. So cannabis cases there appear to need proof of impairment [12].
Exceptions matter too. Michigan State Police say any amount of a Schedule 1 drug or cocaine brings drunk driving penalties, even with no signs of impairment [13]. For a driver with a valid medical marijuana card, the officer must show cannabis impairment [13].
Why a blood THC number is a weak test of impairment
Blood alcohol rises and falls roughly in step with impairment. Forensic toxicologists know THC does not, as NHTSA’s 2017 report to Congress explains [4].
- The peaks don’t line up. Blood THC peaks as smoking ends and drops 80% to 90% within about 30 minutes. Impairment peaks about 90 minutes after smoking [4].
- Blood is drawn late. After a crash or arrest, blood is almost always collected hours after use. By then THC may be low even if impairment remains [4].
- Regular users carry a baseline. A few nanograms can mean recent use, or daily use with no recent dose and no impairment. Some studies have found THC in blood 30 days after use [4].
In a Washington State analysis cited by NHTSA, 62.8% of drivers whom officers believed were cannabis impaired had blood THC below 5 ng/mL. And 24.2% were below 2 ng/mL [4]. A 2016 AAA Foundation for Traffic Safety study of arrested drivers found 70% of cannabis positive drivers below 5 ng/mL. Its authors concluded no THC threshold could be scientifically supported [10].
So a numeric limit can catch a regular user who is no longer impaired and miss an impaired occasional user. Neither result tells you when it is safe to drive.
Cannabis rules in and around the car
Many states also regulate cannabis inside the vehicle. Here are verified examples:
- Using it in the car. Michigan bars drivers from consuming cannabis while driving. It also bars passengers from smoking it in the passenger area on public roads [14]. Minnesota’s 2023 open package law makes it a crime to use cannabis or hemp derived THC products in a vehicle on a street or highway [12].
- Open packages. Minnesota bars opened or partly used cannabis packages in a vehicle on public roads unless they ride in the trunk. Without a trunk, they go where no one sits. The glove box does not count [12].
- Under 21. Every adult use state sets the minimum age at 21 [6]. NCSL notes that South Dakota’s zero tolerance law applies to drivers under 21 [5].
- Medical patients. A medical card is not permission to drive impaired. In Michigan, it changes only what police must prove [13].
- Work drivers. If you drive for work, your employer’s rules may be stricter than state law. See our guide to workplace alcohol, drug and medication policies.
Prescription and over the counter medicines
Drug driving laws cover legal drugs too. NHTSA notes that a label warning about heavy machinery includes driving [2].
The U.S. Food and Drug Administration (FDA) lists medicine types that can make driving unsafe. They include sleep aids, opioids, benzodiazepines, muscle relaxants, antidepressants, antiseizure and antipsychotic drugs, antihistamine cold and allergy products, and cannabis or CBD products [11]. FDA advises reading the Drug Facts label and prescription warnings, and taking a new medicine first when you won’t need to drive [11].
Legally, a prescription shows you were allowed to take the drug, not that you were fit to drive. Minnesota’s statute, for example, allows a prescription defense only to its “any amount” charge for certain controlled substances. It lists no such defense to an under the influence charge [12].
Alcohol plus drugs: the combination problem
NHTSA warns that using 2 or more drugs at once, including alcohol, can amplify the effects of each [2]. Combinations are common in serious crashes. In NHTSA’s trauma center study, 19.9% of injured road users and 33.9% of drivers who died tested positive for 2 or more drug categories [3]. In the AAA Foundation’s arrest data, 77% of cannabis positive drivers also had alcohol or other drugs on board [10].
The law often has a separate path for this. Minnesota’s statute, for example, covers driving under the combined influence of 2 or more substances [12]. So a breath result under .08 may not end a case when a drug is also involved. Our guide to alcohol impaired driving laws by state covers BAC limits.
How police test for drug impairment
There is no breath test for drugs, so officers build a case from several pieces. Each test answers a narrower question than most people assume.
Comparison compiled by Safety Behind the Wheel Foundation
What each test can and cannot show
| Test | What it can show | What it cannot show |
|---|---|---|
| Driving and field sobriety tests | Signs such as weaving, slow responses or trouble following directions [14] | Which drug, if any, caused them |
| Drug Recognition Expert (DRE) evaluation | Whether a driver seems impaired, whether a medical problem could explain it, and the likely drug category [8] | A drug level; accuracy varies across studies [8] |
| Blood test | Which drugs are in the blood, and how much, at the time of the draw [4] | Impairment, especially for THC drawn hours later [4] |
| Urine test | That a drug or its by products were used, sometimes days or weeks earlier [4] | Whether you were under the influence while driving [4] |
| Roadside oral fluid screen | Which drug categories are likely present, within minutes [9] | Amount or impairment; some devices give false positives [9] |
Drug Recognition Experts. DREs are officers trained to run a standardized 12 step evaluation that usually takes about an hour. They sort drugs into 7 categories, from cannabis to narcotic painkillers. In 2022, 8,350 active DREs served all 50 states and DC and completed 23,278 evaluations [8].
Oral fluid. NHTSA reports that, as of 2021, 24 states had laws allowing oral fluid collection from drivers suspected of impairment [9]. As of March 2024, NCSL listed roadside screening programs in Alabama and Indiana and pilots in Michigan and Minnesota [5]. A positive screen can help an officer decide to seek a blood test [9].
Implied consent and warrants. Implied consent laws treat driving as agreement to chemical testing, often including drug tests. Minnesota’s covers blood, breath or urine tests for drugs and cannabis. But a blood or urine test needs a warrant or a recognized exception [12]. In Michigan, refusing a chemical test brings license suspension [14].
Penalties: often the same as alcohol
Many states punish drug impaired driving like drunk driving. Michigan State Police list penalties that can include up to 93 days in jail and a fine of up to $500 [14]. They add license suspension and 6 points, with tougher penalties when a child is in the vehicle [14]. Every state sets its own scale. Repeat offenses or injuries can raise the stakes.
Do drug driving laws reduce crashes?
The evidence is thin. NHTSA’s Countermeasures That Work guide cites a 2016 review that found little evidence that zero tolerance or per se laws reduce cannabis impaired driving. It finds no clear proof that they work better than impairment based laws [7].
That leaves a gap between the legal minimum and best practice. The law asks whether you were impaired or over a limit. Safety asks a simpler question: could anything in your system be slowing you down? If the answer might be yes, don’t drive.
Before you drive: a medication and cannabis check
How to verify your state's law in 5 minutes
- Minute 1: Get oriented. Find your state on GHSA’s drug impaired driving page and note the review date [1]. Treat it as a map, not the law. Our state traffic safety laws hub lists official lookup tools.
- Minute 2: Open the statute. On your state legislature’s website, find the DUI or DWI section. Look for language on drugs, controlled substances and cannabis.
- Minute 3: Name the law type. Look for an “any amount” clause, a numeric THC level or only “under the influence.” Note whether metabolites count and which specimens apply.
- Minute 4: Check the special rules. Look for prescription or medical card defenses, rules for drivers under 21, open package rules and implied consent terms for blood or urine.
- Minute 5: Confirm with an agency. Check your DMV and state highway safety office for recent changes. Save the links and the date you checked.
On a trip through several states, follow the strictest rule on your route.
Frequently asked questions
Can you get a DUI for driving high where cannabis is legal?
Yes. Driving impaired by any drug is illegal in every state and DC, whether the drug is legal or not [2]. Legal adult use covers buying and using cannabis, not driving after it.
What is the legal THC limit for driving?
Most states have none, so prosecutors must prove impairment. GHSA’s table lists 5 states with numeric limits, about a dozen with zero tolerance and Colorado’s inference at 5 ng/mL [1]. NHTSA says no blood level reliably marks impairment [4].
Can I be charged if I used cannabis days ago?
Possibly, in a zero tolerance state that counts THC metabolites. Metabolites can be detected days to weeks after use, long after the effects wear off [1, 7]. In impairment based states, the state must show you were impaired while driving.
The bottom line
Recommendation from Safety Behind the Wheel Foundation
Know your state’s law, but don’t drive by the numbers. If you’ve used cannabis, a new or sedating medicine, or any mix with alcohol, plan a different ride. Treat feeling fine as no proof at all.
Related articles
- Drug and medication impaired driving: know your risk before you drive
- DUI and DWI laws by state: BAC limits, suspensions and interlocks
- State traffic safety laws: how to look up and verify your state’s rules
- Alcohol impaired driving: know the risks and plan a sober ride home
- Workplace driving impairment: alcohol, drug and medication policies
Sources and further reading
- 1Governors Highway Safety Association (GHSA). Drug-Impaired Driving (issue overview and state law table). Overview updated June 2026; laws reviewed by state highway safety offices June 2025; table updated October 2025. ghsa.org/state-laws-issues/drug-impaired-driving
- 2National Highway Traffic Safety Administration (NHTSA). Drug-Impaired Driving. No date shown; accessed October 3, 2026. nhtsa.gov/risky-driving/drug-impaired-driving
- 3Thomas FD, Darrah J, Graham L, et al. Alcohol and Drug Prevalence Among Seriously or Fatally Injured Road Users. NHTSA, DOT HS 813 399. December 2022. rosap.ntl.bts.gov/view/dot/65623
- 4NHTSA. Marijuana-Impaired Driving: A Report to Congress. DOT HS 812 440. July 2017. nhtsa.gov/…/812440-marijuana-impaired-driving-report-to-congress.pdf
- 5National Conference of State Legislatures (NCSL). Drugged Driving: Marijuana-Impaired Driving. Updated March 27, 2024. ncsl.org/transportation/drugged-driving-marijuana-impaired-driving
- 6Insurance Institute for Highway Safety (IIHS). Alcohol and Drugs (research area overview). Updated August 2026. iihs.org/research-areas/alcohol-and-drugs
- 7NHTSA. Countermeasures That Work: Drug-Impaired-Driving Laws. No date shown; accessed October 3, 2026. nhtsa.gov/book/countermeasures-that-work/…/legislation-and-licensing/drug
- 8NHTSA. Countermeasures That Work: Enforcement of Drug-Impaired Driving. No date shown; accessed October 3, 2026. nhtsa.gov/book/countermeasures-that-work/…/enforcement/enforcement-drug
- 9NHTSA. Countermeasures That Work: Drug-Impaired Driving, Emerging Issues. No date shown; accessed October 3, 2026. nhtsa.gov/book/countermeasures-that-work/drug-impaired-driving/emerging-issues
- 10Logan B, Kacinko SL, Beirness DJ. An Evaluation of Data from Drivers Arrested for Driving Under the Influence in Relation to Per se Limits for Cannabis. AAA Foundation for Traffic Safety. May 2016. aaafoundation.org/research/…per-se-limits-cannabis
- 11U.S. Food and Drug Administration (FDA). Some Medicines and Driving Don’t Mix. Consumer update. March 12, 2024. fda.gov/consumers/…/some-medicines-and-driving-dont-mix
- 12Minnesota Office of the Revisor of Statutes. Minnesota Statutes 2025, Chapter 169A (sections 169A.20, 169A.36, 169A.46 and 169A.51). Accessed October 3, 2026. revisor.mn.gov/statutes/cite/169A
- 13Michigan State Police, Office of Highway Safety Planning. Impaired Driving. No date shown; accessed October 3, 2026. michigan.gov/msp/…/safety-programs/impaired-driving
- 14Michigan State Police, Office of Highway Safety Planning. Cannabis and Driving. No date shown; accessed October 3, 2026. michigan.gov/msp/…/cannabis-and-driving
- 15Colorado Department of Transportation (CDOT). Natural Medicine: Never Drive on Mushrooms or Other Psychedelics. Last modified February 26, 2026. codot.gov/safety/impaired-driving/natural-medicine
This article reflects the priorities of traffic safety law and clinical and forensic toxicology. It is general education, not legal or medical advice for any individual, charge or case. Talk with a lawyer licensed in your state about a legal matter and with your clinician or pharmacist about your medicines. Laws, testing rules and data change, so verify details with official sources. Reviewed October 2026.
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