Why Per Se Cannabis DUI Laws Punish Sober Drivers

For decades, driving under the influence laws were built on a simple and reasonable principle: punish impairment, not presence. Alcohol laws attempt to do exactly that by using blood alcohol concentration as a proxy for real-time intoxication. Cannabis has been forced into the same legal framework that, unfortunately, ignores pharmacology, individual biology, and modern science when it comes to cannabis DUIs.

A groundbreaking 2025 study¹ published in Clinical Chemistry exposes just how deeply flawed cannabis “per se” DUI laws truly are. The findings confirm what patients, clinicians, and advocates have been saying for years: you can be sober, unimpaired, and still be legally guilty of a DUI simply because you used cannabis days earlier.

If you’re not high, you shouldn’t get a DUI, and now science backs that up unequivocally.

What Are Per Se Cannabis DUI Laws?

Per se DUI laws set a fixed blood concentration threshold for delta-9-THC. This is commonly 2 ng/mL or 5 ng/mL, which automatically constitutes legal impairment. Some states go even further, enforcing zero-tolerance laws, where as little as 0.5 ng/mL can result in criminal charges.

The problem is devastating for many cannabis consumers. THC blood concentration does not necessarily correlate reliably with impairment, especially in regular or medical cannabis patients. Unlike alcohol, THC is fat-soluble, accumulates in the body, and can be released into the bloodstream long after any psychoactive effects have disappeared.

Yet under current laws, presence equals guilt, regardless of actual impairment.

What the 2025 Clinical Chemistry Study Found

The 2025 open-access study, Per Se Driving Under the Influence of Cannabis Statutes and Blood Delta-9-THC Concentrations following Short-Term Cannabis Abstinence, examined 190 regular cannabis consumers who abstained from cannabis for at least 48 hours. This is critical as participants were not acutely intoxicated but were intentionally sober. Despite this, the results were startling.

Nearly 43% of participants exceeded zero-tolerance THC thresholds before any new cannabis use. Almost one in four exceeded the 2 ng/mL per se limit, and 5.3% exceeded the 5 ng/mL threshold. These levels would automatically trigger DUI charges in many states. One participant even registered 16.2 ng/mL after two full days of abstinence.

Even more concerning, simulated driving performance showed no difference between participants above these legal limits and those below them. In other words, the law labeled them impaired, but science did not.

This is not a loophole, but a failure of justice baked into statute.

Medical Cannabis Patients Are Being Set Up to Fail

For medical cannabis patients, this legal framework is especially cruel.

Patients treating chronic pain, PTSD, multiple sclerosis, cancer-related symptoms, epilepsy, or autoimmune disorders often require higher and more frequent doses to achieve therapeutic effects. Many use cannabis daily, not recreationally, but as medicine.

Because THC accumulates in the body over time, daily medical use almost guarantees detectable blood THC levels at all times, even when patients are completely sober. Under per se laws, this means a patient could be “legally impaired” every single day of their life, despite being sober.

These patients are not reckless, nor are they intoxicated. They are compliant with medical recommendations and still face arrest, prosecution, license suspension, job loss, and stigma.

You Can Get a DUI 48 Hours After Using Cannabis

One of the most alarming findings from the study is how long THC remains detectable at legally relevant levels. Participants who abstained for two full days still exceeded DUI thresholds. That means someone who consumed cannabis on a Friday night could be arrested on Monday morning and charged with a DUI, even if they were completely sober and driving perfectly.

No other legal substance works this way.

Imagine being arrested for drunk driving because you had a glass of wine two days ago. The idea would be laughable, yet this is exactly how cannabis laws function today.

Why THC Blood Levels Fail to Measure Driving Impairment

Perhaps the most important finding in the study is that there was no measurable difference in driving performance between those who exceeded THC thresholds and those who did not. This dismantles the core assumption behind per se laws that a specific THC concentration equals impairment.

Driving impairment is complex. It involves reaction time, attention, coordination, decision-making, fatigue, medication interactions, and individual tolerance. Blood THC levels alone cannot capture any of that. By relying on arbitrary numbers instead of real-world impairment, the law abandons science in favor of convenience.

The Real-World Consequences Are Severe

Per se cannabis DUI laws do not just exist on paper. They can destroy lives.

People lose jobs that require clean driving records, parents face custody challenges, and patients avoid their medicine out of fear. Trust in law enforcement also erodes, and courts become overrun with cases that have nothing to do with actual unsafe driving. Truly impaired drivers are not better identified under these laws, but innocent people are being criminalized under them.

Impairment-Based DUI Testing: What Science Supports

Impairment-based assessments exist. Behavioral evaluations, cognitive testing, roadside performance measures, and technology-assisted assessments all offer more accurate, fair approaches than blood THC limits.

Alcohol laws evolved as science improved, and cannabis laws must do the same.

This study does not argue against responsible enforcement, but it emphasizes the need for evidence-based enforcement. The kind that is rooted in science and protects public safety without criminalizing sober people.

If You’re Not High, You Shouldn’t Get a DUI

That is not a slogan, but a principle rooted in science, fairness, and basic justice.

The study confirms what patients and advocates have long known: per se cannabis DUI laws are unscientific, ineffective, and harmful. They punish biology, not behavior, criminalize medicine, and confuse presence with impairment.

It’s time for lawmakers to listen to the data, because if you’re not high, you shouldn’t get a DUI.

^References:

^{1. Robert L Fitzgerald, Anya Umlauf, Raymond T Suhandynata, David J Grelotti, Marilyn A Huestis, Kyle F Mastropietro, Igor Grant, Thomas D Marcotte, Per Se Driving Under the Influence of Cannabis Statutes and Blood Delta-9-Tetrahydrocannabinol Concentrations following Short-Term Cannabis Abstinence, Clinical Chemistry, Volume 71, Issue 12, December 2025, Pages 1225–1233, https://doi.org/10.1093/clinchem/hvaf121}