Since recreational marijuana became legal, Colorado drivers have faced growing confusion about how cannabis use affects DUI laws. Both alcohol and marijuana impairment fall under the same statute, but the standards for proof, testing, and penalties differ in key ways. Understanding those distinctions can help drivers make informed decisions—and respond strategically if charged.
How Colorado Defines Alcohol DUI and DWAI
Colorado law makes it illegal to drive under the influence of alcohol when a person is substantially incapable of safe driving or has a blood alcohol concentration (BAC) of 0.08% or higher within two hours of driving, under C.R.S. § 42-4-1301. A related offense, Driving While Ability Impaired (DWAI), applies when a person’s ability to drive safely is affected to the slightest degree by alcohol.
How Colorado Defines Marijuana DUI and DWAI
The same statute covers marijuana, listing “one or more drugs” among the substances that can cause impairment. For marijuana, however, the law creates a permissible inference—not a strict limit. If a chemical test finds five nanograms or more of active delta-9 THC per milliliter of whole blood, jurors may infer impairment under C.R.S. § 42-4-1301(6)(a)(IV).
Because that inference can be challenged with evidence of tolerance, timing, or normal behavior, marijuana DUIs are often more subjective than alcohol cases.
Alcohol Per Se vs. Marijuana’s Permissible Inference
The biggest difference between alcohol and cannabis DUIs lies in how impairment is proven. Alcohol has an objective, numerical standard: a BAC of 0.08% means you are legally intoxicated. Marijuana has no such automatic threshold. The five-nanogram standard merely allows—but doesn’t require—a finding of impairment. That difference often shapes how these cases are charged and defended in Colorado courts.
How Testing Works for Alcohol vs. Marijuana
When officers have probable cause for a DUI, Colorado’s express consent law (C.R.S. § 42-4-1301.1) requires drivers to take a chemical test. Alcohol testing typically involves a roadside breath test or an evidentiary breath or blood draw.
Marijuana testing requires a blood sample, since breathalyzers cannot measure THC. Timing is critical; THC levels drop quickly, sometimes within an hour, which can make late testing unreliable. Defense attorneys often challenge the timing and accuracy of these samples.
Penalties for Marijuana and Alcohol DUIs
Penalties for both substances fall under the same framework in C.R.S. § 42-4-1307. A first-offense DUI—whether from alcohol, marijuana, or both—can bring five days to one year in jail, fines up to $1,000, license suspension, and mandatory education or treatment.
DWAI carries slightly lower penalties but still results in a criminal record and possible jail time. Repeat offenses raise the stakes, and a fourth DUI conviction is a class 4 felony with possible prison time.
Common Issues in Marijuana DUI Cases
THC is fat-soluble, meaning it can remain in the body long after its psychoactive effects fade. This makes it harder to determine when impairment actually occurred. Blood test results alone don’t tell the full story, which is why officers rely heavily on driving behavior, field sobriety tests, and their own observations. A defense attorney can question whether the state’s evidence truly proves impairment at the time of driving or simply shows prior marijuana use.
DWAI and Combined Use Cases
Colorado’s DWAI standard—“affected to the slightest degree”—often applies in marijuana cases with low THC readings. Prosecutors may pursue DWAI when impairment evidence is weak or when both alcohol and cannabis are involved. Combined use can heighten perceived impairment, even when neither substance alone would exceed its legal threshold.
That’s why understanding both definitions under C.R.S. § 42-4-1301 is essential for anyone charged with a drug-related driving offense.
Key Takeaways for Drivers
In practice, alcohol DUIs rely on a fixed number, while marijuana DUIs rely on interpretation. A five-nanogram THC result doesn’t automatically prove guilt. A skilled attorney can rebut that inference with expert testimony or evidence of normal performance.
Both offenses share similar penalties and license consequences, but marijuana cases often depend more on subjective judgment calls by police and prosecutors.
Facing a Marijuana DUI Charge? Talk to MBS Law
Colorado’s marijuana DUI laws demand a defense built on science, procedure, and statutory precision. MBS Law’s attorneys know how to challenge the five-nanogram inference, question testing protocols, and evaluate every step of your stop and arrest.
If you’re facing a marijuana DUI or DWAI charge, contact our office to speak with a cannabis DUI lawyer in Denver who understands the law, the process, and the best path forward for your case.
