Colorado legalized recreational marijuana in 2012, but legal use has never meant legal to drive. That distinction matters if you’ve been arrested and are wondering whether a blood test reading above 5 ng/mL sealed your fate. It didn’t. Colorado’s marijuana DUI law doesn’t work the way most people assume, and that gap between assumption and reality is exactly where a defense is built.
Since 1990, we’ve handled thousands of DUI cases across the Denver metro area. We’ve seen the full range of marijuana-related charges. From a first-time recreational user pulled over after a concert to a medical marijuana patient who tested at 8 ng/mL sixteen hours after their last dose, the law treats these situations with more nuance than the charging document suggests. Understanding that nuance is the first step.
How Colorado’s Marijuana DUI Law Actually Works
The governing statute is C.R.S. 42-4-1301. Under it, a driver faces a DUI charge if marijuana rendered them substantially incapable of safely operating a vehicle, or a DWAI (driving while ability impaired) charge if marijuana affected their driving to even the slightest degree. Both charges apply regardless of whether the marijuana was used legally, recreationally or medically.
The 5 ng/mL threshold for delta-9 THC, the primary psychoactive compound in cannabis, triggers what the law calls a permissive inference. A permissive inference means a jury is permitted to infer impairment from that number, but isn’t required to. The prosecution still must prove actual impairment beyond a reasonable doubt. This is fundamentally different from the 0.08% BAC rule for alcohol, which is a per se limit where the number alone establishes the legal violation. With marijuana, the number opens a door. It doesn’t close the case.
That distinction works in both directions. A driver can also be arrested with THC levels below 5 ng/mL if the officer observes and documents impairment. The Colorado Department of Transportation confirms that the primary determinant is observed driving behavior, not the blood result in isolation.
Why the Blood Test Isn’t the End of the Case
THC behaves differently in the body than alcohol. It’s fat-soluble and stores in body fat, which means chronic users and medical marijuana patients can register at or above 5 ng/mL hours or even days after their last use, with no active psychoactive effect. Peer-reviewed research documenting this pharmacokinetic reality is admissible at trial and forms the basis of testimony in these cases.
There are additional vulnerabilities in how marijuana blood evidence is collected and processed. Colorado requires whole-blood testing, which means the evidence travels through phlebotomy at the collection site, transport to a laboratory, intake and storage, processing, and analyst review before it produces a reported number. Each step is governed by protocol, and each step is a potential defect point for chain-of-custody challenges.
Timing matters too. There’s typically a 30-to-90-minute gap between a traffic stop and an actual blood draw. THC concentrations decline over that window. When the result lands near the 5 ng/mL threshold, the concentration at the time of driving may have been meaningfully different from the concentration at the time of testing, and that gap belongs to the defense.
How Law Enforcement Builds a Marijuana DUI Case
Understanding how a case is constructed helps identify where it can be challenged. Officers must first establish probable cause through observed driving behavior and traffic violations before initiating a DUI investigation at all. Possessing a medical marijuana card doesn’t, on its own, constitute probable cause for a blood test under Colorado law.
The Drug Recognition Expert Evaluation
When impairment from drugs rather than alcohol is suspected, many agencies deploy a Drug Recognition Expert, or DRE. A DRE is an officer trained under the International Association of Chiefs of Police 12-step evaluation protocol, which includes pupil measurement under different lighting conditions, vital-sign monitoring, divided-attention tests, and structured interrogation. Colorado currently has 226 active DREs representing 79 law enforcement agencies statewide, including 62 with the Colorado State Patrol, according to CDOT.
That evaluation carries significant weight with juries, but it isn’t immune to challenge. All 12 steps must be completed in sequence. Any deviation (a missed step, an out-of-order sequence, or a lapsed DRE certification) can undermine the opinion. Equally important is the differential diagnosis requirement: the DRE must rule out medical conditions that could explain the observed signs. When the officer’s drug-category opinion conflicts with toxicology results, that inconsistency becomes a defense argument.
Field Sobriety Tests & Their Limitations
Standardized field sobriety tests (the walk-and-turn, one-leg stand, and horizontal gaze nystagmus) were developed and validated for alcohol impairment. Their scientific reliability as indicators of THC impairment is actively contested in the research literature. This creates a defense angle that simply doesn’t exist in a straightforward alcohol DUI case, and it’s one we routinely explore.
The Parallel DMV Proceeding Most Defendants Overlook
A marijuana DUI arrest in Denver sets two separate legal proceedings in motion simultaneously. The criminal case moves through Denver County Court for misdemeanor charges, or the Lindsey-Flanigan Courthouse at 520 W Colfax Avenue for felony DUI, vehicular assault, or vehicular homicide charges. At the same time, an entirely separate civil proceeding begins before the Colorado Division of Motor Vehicles (DMV) concerning your driving privileges.
The detail that catches most people off guard is the deadline. You have 7 calendar days from the date of the DMV notice to request a hearing. Miss that window and your license is automatically revoked, regardless of how the criminal case eventually resolves. A not-guilty verdict at trial doesn’t restore a license lost because no hearing was requested in time.
Refusing a blood test creates its own complications. Under Colorado’s express consent law, codified in C.R.S. 42-4-1301.1, a refusal carries administrative penalties and the prosecutor can use the refusal as evidence against you in the criminal case. Neither choice is consequence-free, which is why having an attorney involved before any decisions are made matters so much.
Defense Strategies That Can Challenge a Marijuana DUID Charge
Every case is different, but there are several well-established defense angles we examine in marijuana DUID matters.
Fourth Amendment & Suppression Challenges
The strongest challenges often begin before the blood test. If the officer lacked reasonable articulable suspicion to initiate the traffic stop in the first place, everything gathered after that moment (including blood results, DRE opinions, and field sobriety observations) may be suppressible on Fourth Amendment grounds. A suppression motion that succeeds can effectively end the prosecution.
DRE Protocol & Blood Evidence Review
Where suppression isn’t available, we scrutinize the DRE evaluation for protocol issues including step completion, sequencing, certification currency, and differential diagnosis. We also examine the entire blood evidence chain of custody for collection, labeling, transport, and storage deficiencies.
Chronic-User Pharmacokinetics
For habitual users and medical marijuana patients, testimony on chronic-user delta-9 THC pharmacokinetics can directly rebut the 5 ng/mL permissive inference. A qualified witness can explain to a jury why a person’s blood concentration at the time of testing reflects their history of use rather than their level of impairment while driving, and why those aren’t the same thing. This argument is grounded in peer-reviewed science, and juries can follow it.
When Alcohol & Marijuana Are Both Involved
Combination cases (where both alcohol and marijuana are detected) are common and add complexity in both directions. The prosecution can use each substance to support an impairment argument for the other. At the same time, the interaction between alcohol and THC pharmacokinetics is genuinely difficult to model, and that complexity creates additional surface area for challenges on the causation question. These cases require careful coordination between toxicology analysis and legal strategy, and they aren’t ones to navigate without experienced counsel.
CDOT reports that more than 60 people are arrested every day in Colorado for DUI involving drugs, alcohol, or a combination of both. Many of those arrests involve people who used marijuana legally and have no prior criminal history. A charge isn’t a conviction, and the permissive inference framework exists precisely because the Colorado legislature recognized that a blood number alone can’t fairly determine guilt.
If you’ve been arrested for a marijuana DUI in Denver, the 7-day DMV deadline means time is short. Fife Luneau, P.C. has been defending DUI cases in Denver since 1990, and our attorneys are available around the clock at (720) 408-7130 to talk through your situation.