Driving under the influence of marijuana is a serious charge in Colorado, but there’s widespread confusion about how it’s detected, especially when it comes to breath tests. Can a breathalyzer detect weed during a DUI stop in Greeley? The answer is no. Breathalyzers are designed to detect alcohol, not THC, the active compound in cannabis.
At McAdams Law Office, we help drivers facing marijuana-related DUI allegations understand the real science behind roadside testing and protect their rights. As a trusted Greeley DUI Defense Attorney, we’re dedicated to challenging flawed evidence and building a strong defense for our clients.
Breathalyzers are designed to measure alcohol, not cannabis. These devices analyze exhaled air for alcohol molecules to estimate blood alcohol concentration (BAC). Alcohol is water-soluble, so it enters the lungs quickly, allowing accurate breath readings.
THC is fat-soluble and doesn’t transfer easily into breath samples. As a result, ignition interlock devices and breathalyzers cannot detect THC or cannabis use. Researchers are developing tools to identify marijuana impairment at the roadside, but no such technology has been successfully implemented. Unlike alcohol, detecting THC is scientifically complex and requires specialized methods still in development.
Breathalyzers don’t detect marijuana or THC. Even with a 0.00 BAC, officers may suspect impairment from behavior, odor, or speech, leading to further testing. Secondhand smoke won’t trigger a breathalyzer, but suspicion can escalate an investigation.
Marijuana presents unique challenges for DUI enforcement. THC stays in the body long after its effects have worn off, making it hard to connect current impairment with a specific THC level. Key difficulties include:
Because of these issues, the presence of THC alone isn’t always enough to prove a driver was impaired, and can a breathalyzer detect weed remains a question many drivers ask, for good reason.
In Colorado, officers don’t need a failed chemical test to make an arrest. If your driving appears impaired, even slightly, you can be charged. They are trained to identify signs of intoxication, like slow response time, slurred speech, red eyes, or inconsistent behavior.
Marijuana impairment is linked to Delta-9-tetrahydrocannabinol (Delta-9 THC). It affects judgment, coordination, and perception, but its presence in the blood doesn’t always reflect recent use.
According to Colorado Law, a blood test showing five ng/mL of active Delta-9 THC creates a “permissible inference” of impairment. Drivers can face DUI charges even with lower THC levels if the officer documents signs of drug use. Police often rely on:
Urine tests for THC metabolites are unreliable for DUI cases, as they detect past use, not active impairment. Metabolites remain in the body for days or weeks, leading to positive tests long after marijuana’s effects fade.
Blood tests, though more reliable than urine tests for THC, have limitations. While they show active THC levels, there’s no set impairment concentration. Colorado’s five ng/mL infers impairment, but needs corroborating evidence.
Hair tests show long-term use but not recent impairment. They’re rarely used in DUI cases, as they can’t determine if someone was under the influence at the time of arrest.
Police can initiate a traffic stop based on reasonable suspicion of impairment. Common triggers include speeding, weaving, or failure to signal. Officers observe your behavior and may administer field tests or request a chemical sample.
Yes, driving high is treated just like driving drunk under Colorado law. According to CRS § 42-4-1301, a person commits DUI by operating a vehicle while under the influence of one or more drugs, alcohol, or a combination of both. Here’s what that means:
Can a breathalyzer detect weed in these cases? Still no. Officers rely on what they see, not breath test results, when handling marijuana DUIs.
Charged with driving under the influence of marijuana, and asking the question: Can a breathalyzer detect weed? McAdams Law Office is ready to defend you. We challenge faulty tests, flawed traffic stops, and weak evidence. Call (970) 353-0002 now for a confidential consultation.
William T. McAdams, known as Bill, is a highly experienced criminal defense attorney and former prosecutor. Since establishing McAdams Law Office in 2006, he has represented clients in cases including DUI, domestic violence, and theft, handling over 100 jury trials. Bill serves clients predominantly in Weld and Larimer counties, including Greeley, Evans, Windsor, Loveland, and Fort Collins. An active community volunteer and member of multiple legal associations, he is dedicated to protecting his clients’ rights.
This page has been written, edited, and reviewed by a team of legal writers following our comprehensive editorial guidelines. This page was approved by Founding Partiner, William McAdams who has more than 25 years of legal experience as a personal injury attorney.