Why Colorado’s 5 Nanogram THC Limit Is Scientifically Meaningless, But Still Legally Devastating
In a recent discussion, attorney Bradley Smith of Smith and Widinger breaks down why Colorado’s five nanogram THC limit creates confusion and serious risk for drivers. Many people assume marijuana DUI laws work like alcohol laws, but that assumption can lead to devastating consequences in court.
Most drivers understand alcohol limits. Years of public education have reinforced that a blood alcohol level of 0.08 can, by itself, support a DUI conviction. THC does not work the same way. Colorado uses an “inferred” or implied limit of five nanograms of THC per milliliter of blood, but there is no clear scientific agreement that this number proves impairment while driving.
One major problem is that THC affects people very differently. Unlike alcohol, THC can remain in the bloodstream long after any psychoactive effects have worn off. A regular user may test above five nanograms even when they are not impaired at all. Even experts—including those working with state agencies—often disagree on what THC blood levels actually mean in real-world driving situations.
THC blood tests are also far more complex than alcohol tests. Instead of a single, easy-to-understand number, marijuana blood reports can include multiple measurements, including Delta-9 THC, which prosecutors often rely on to argue impairment. However, scientific studies linking specific THC levels to unsafe driving are limited. That gap leaves room for interpretation, disagreement, and error.
Despite these weaknesses, the legal consequences are very real. Prosecutors may argue that anything over five nanograms automatically equals a DUI. But in court, the burden is higher. The state must prove impairment beyond a reasonable doubt, not just suggest it’s “more likely than not.” Without a strong defense, juries may never hear how uncertain the science truly is.
How an Experienced DUI Attorney Makes a Difference
An attorney who understands both the law and the science can challenge the assumptions behind the five nanogram limit. This includes questioning how the blood test was conducted, what the numbers actually show, and whether they truly reflect impairment at the time of driving. A knowledgeable advocate can also expose inconsistencies in expert testimony and highlight the lack of clear scientific proof.
Rather than accepting the state’s interpretation at face value, an experienced attorney acts as a safeguard—making sure the jury understands that THC cases are not as simple as alcohol cases and that uncertainty matters under the law.
Take Action Today: Protect Your Rights After a Marijuana DUI
If you are facing a marijuana DUI in Colorado, the five nanogram limit should not go unchallenged. The stakes are high, and the science is far from settled. Speaking with an attorney who understands these issues can make a critical difference in protecting your rights and your future.
FAQs
Is five nanograms of THC the same as a 0.08 alcohol limit?
No. Unlike alcohol, the five nanogram THC limit is not based on clear scientific proof of impairment and is only an inferred standard.
Can I be charged even if I wasn’t impaired?
Yes. THC can stay in your system long after impairment ends, which means drivers can test above the limit without being unsafe.
Why are THC DUI cases harder to understand?
THC blood tests can include multiple measurements, and there is limited research connecting specific levels to driving ability.
Do I need an attorney for a marijuana DUI?
Because these cases rely on complex science and legal assumptions, having an attorney who can challenge the evidence is extremely important.