With marijuana now legal for medical or recreational use in many states, a new legal question has emerged: What happens if you’re caught driving high? Unlike alcohol, where impairment is measured by blood alcohol concentration (BAC), marijuana presents a host of legal gray areas that make enforcement and prosecution more complex.
In this post, we’ll break down the legal landscape of marijuana DUIs, including how laws vary by state, how impairment is determined, and what drivers need to understand before getting behind the wheel.
Is It Illegal to Drive High?
Yes, in all 50 states, it is illegal to operate a motor vehicle while impaired by marijuana—even if cannabis is legal in your state.
However, the challenges lie in proving impairment. While breathalyzers and BAC levels are used for alcohol-related DUIs, marijuana doesn’t metabolize the same way. There’s no national standard for THC levels that equates to impairment, which leads to a lot of confusion.
The Problem with Measuring Marijuana Impairment
Unlike alcohol, THC (the psychoactive compound in cannabis) behaves very differently in the body:
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THC can be detectable in your system for days or weeks, long after the high has worn off.
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Regular users may have higher residual THC levels but no impairment.
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There’s no universally accepted threshold (like 0.08% for alcohol) to prove someone is too high to drive.
This means that a driver could test positive for marijuana in a drug test even if they’re not impaired at the time they’re driving.
Zero-Tolerance vs Per Se Laws
States generally handle marijuana DUIs in three different ways:
1. Zero-Tolerance States
In these states, any detectable amount of THC in your system while driving is enough to charge you with a DUI. Examples include:
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Utah
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South Dakota
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Georgia
This approach doesn’t distinguish between current impairment and past use, which can unfairly impact medical users or frequent recreational users.
2. Per Se THC Limit States
Some states have set a legal limit for THC, usually 1–5 nanograms per milliliter of blood. Examples:
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Colorado (5 ng/mL)
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Washington (5 ng/mL)
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Montana (2 ng/mL)
Critics argue that these limits are not scientifically consistent and may not reflect actual impairment.
3. Effect-Based Laws
These states rely on observable signs of impairment, not specific THC levels. Officers use behavioral cues like:
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Bloodshot eyes
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Slowed reaction time
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Poor coordination
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Odor of marijuana
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Admission of recent use
States with effect-based laws include:
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California
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Texas
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Oregon
Field Sobriety Tests and Drug Recognition Experts (DREs)
Because there’s no roadside THC breathalyzer (yet), officers often rely on field sobriety tests and evaluations by Drug Recognition Experts (DREs) to assess impairment.
However, these evaluations can be:
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Subjective
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Inconsistent
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Affected by other conditions (fatigue, anxiety, etc.)
The lack of standardized testing makes marijuana DUI enforcement vulnerable to legal challenges.
Can Medical Marijuana Patients Be Charged with DUI?
Yes. Even if you’re a registered medical marijuana patient, you can still be charged with DUI if an officer believes you’re impaired while driving.
However, in some states, medical users can use their prescription as part of their legal defense. The key point remains: legal use doesn’t equal legal impairment.
Consequences of a Marijuana DUI
A cannabis-related DUI conviction can result in:
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Fines and court costs
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License suspension
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Mandatory drug education or treatment
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Probation or jail time
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Higher insurance premiums
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Criminal record
Penalties often mirror those for alcohol DUIs, even though impairment is harder to prove.
Legal Defenses for Marijuana DUI Charges
Because of the gray areas, marijuana DUI cases often hinge on:
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Challenging the test results (e.g., time between arrest and blood draw)
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Questioning the officer’s training or observations
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Highlighting medical use and lack of actual impairment
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Lack of evidence connecting THC levels to poor driving behavior
Hiring a qualified DUI defense attorney is essential to navigate these complex issues.
Future of Marijuana DUI Laws
With cannabis legalization expanding, states are beginning to:
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Explore THC breath testing technology
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Invest in training officers as DREs
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Reconsider per se THC limits
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Develop more accurate roadside screening tools
Until then, confusion will persist, and drivers need to be cautious.
Conclusion
Driving under the influence of marijuana remains illegal nationwide, but proving impairment is far more complicated than with alcohol. There’s no national THC limit, and current testing methods can produce misleading results. This legal gray area puts both drivers and law enforcement in difficult positions.
If you’re using marijuana—recreationally or medically—it’s crucial to understand your state’s laws and err on the side of caution. When in doubt, don’t drive high. It’s not worth the legal risk, the potential for an arrest, or the safety concerns.
