How Police Test for Marijuana in DUI Stops in Virginia

 Posted on September 17, 2025 in Drug DUI

When Virginia legalized small amounts of marijuana for personal use, many drivers assumed that using cannabis and driving would be treated the same way as having a glass of wine with dinner. However, that assumption can lead to serious legal trouble.

Driving under the influence of marijuana is a criminal offense under Virginia law. Police officers across the state use multiple methods to detect marijuana DUI. If you have been charged, you still have the right to challenge the allegations, and our McLean, VA marijuana DUI defense lawyers can help.

Is Marijuana Illegal in Virginia?

Virginia law permits adults 21 and older to possess up to one ounce of marijuana under Virginia Code § 4.1-1100. However, driving after using weed is still illegal under Virginia Code § 18.2-266. Unlike alcohol DUIs, no set THC limit automatically proves impairment. Instead, prosecutors must rely on evidence like officer observations and testing to show a driver was under the influence at the time of the stop.

Methods for Testing for Marijuana DUI in Virginia

When an officer suspects marijuana impairment, several methods may be used:

• Roadside observations: Officers often cite bloodshot eyes, the smell of marijuana, and slowed responses as signs of possible impairment.

• Field sobriety tests: Officers may ask you to walk in a straight line, follow a pen with your eyes, or stand on one leg to test for sobriety. While common in alcohol cases, these tests are less reliable for cannabis.

• Blood testing: Because marijuana does not show up on a breath test, officers may request a blood test. This looks for THC and its metabolites, which can remain in the body long after the effects of marijuana have faded.

• Statements or admissions: Anything a driver says about recent marijuana use can also be used to support the officer’s suspicion.

Under Virginia’s implied consent law, drivers lawfully arrested for DUI are required to submit to testing. However, the science around marijuana impairment remains debated, which can create openings for the defense.

Possible Defenses for a Marijuana DUI in Virginia

Several defenses may apply in a marijuana DUI case. One is challenging the validity of the traffic stop itself. If the officer did not have reasonable suspicion to pull you over, your attorney be able to argue that any evidence gathered afterward should be thrown out.

Another common defense involves questioning the reliability of field sobriety tests, since they are not designed to measure marijuana impairment. Blood test results may also be contested. THC levels vary widely between individuals, and a positive test does not necessarily mean you were impaired at the time of your arrest. Additionally, mistakes made when the sample was collected, stored, or analyzed can create grounds to challenge the evidence.

Contact a Vienna, VA Marijuana DUI Defense Attorney for a Free Consultation

At Arrested for a DUI, LLC, our attorneys bring more than 30 years of combined experience to every case. We are dedicated to protecting our clients’ rights and proud to serve as strong advocates for the Hispanic community. Our team frequently engages with local and national conversations on issues affecting Latin Americans and immigrants.

If you are accused of driving under the influence of weed, call us today at 301-479-5466 to schedule a free consultation with our dedicated McLean, VA marijuana DUI defense lawyers. We will fight to protect your license, your record, and your future. Se habla Español.