Las Vegas DUI Defense Lawyer

Inside a DUI Stop: How Law Enforcement Tests for Marijuana Impairment in Las Vegas

DUI stops, or traffic stops for driving under the influence, are a critical part of law enforcement’s efforts to keep roads safe. With the increasing prevalence of marijuana use, officers must also be vigilant for drivers impaired by cannabis. In this blog post, we’ll take a closer look at what happens during a DUI stop and how law enforcement tests for marijuana impairment.

The DUI Stop Process:

  • Initial Observation: Officers typically initiate a DUI stop based on observed behavior such as erratic driving, speeding, or running red lights.
  • Pulling Over: Once signaled by law enforcement, the driver should pull over to a safe location on the side of the road.
  • Interaction: Officers approach the vehicle and engage in a dialogue with the driver, requesting license, registration, and proof of insurance.

Assessing Marijuana Impairment:

  • Field Sobriety Tests (FSTs): Officers may administer FSTs to assess a driver’s physical and cognitive abilities. Common FSTs include the walk-and-turn test, the one-leg stand test, and the horizontal gaze nystagmus (HGN) test.
  • Observational Indicators: Law enforcement officers may look for signs of marijuana impairment, such as bloodshot eyes, dilated pupils, and the odor of marijuana emanating from the vehicle.
  • Chemical Testing: If officers suspect marijuana impairment, they may request a chemical test to measure THC levels in the driver’s system. This can involve blood, breath, or urine testing, although blood tests are considered the most accurate for detecting THC.

Field Sobriety Tests for Marijuana Impairment:

  • Challenges and Limitations: Unlike alcohol, where impairment is relatively straightforward to measure, detecting marijuana impairment presents unique challenges. FSTs for marijuana are less standardized and may be influenced by factors such as individual tolerance and experience.
  • Interpretation: Officers assess performance on FSTs based on established criteria, looking for indicators of impairment such as poor balance, lack of coordination, and inability to follow instructions.
  • Legal Considerations: Results of FSTs for marijuana impairment may be used as evidence in DUI cases, but their reliability and admissibility can be subject to legal challenges.

Chemical Testing for THC Levels:

  • Blood Testing: Blood tests are considered the most reliable method for detecting THC in the body and are often used to confirm marijuana impairment in DUI cases.
  • Breath Testing: Breath tests are less common for marijuana impairment due to the challenges of accurately measuring THC levels in breath.
  • Urine Testing: Urine tests may be used as a less invasive method for detecting THC but are generally less reliable and may not accurately reflect impairment at the time of driving.


DUI stops are a critical tool for law enforcement in identifying and deterring impaired driving, including impairment due to marijuana use. Understanding how officers assess marijuana impairment during a DUI stop can help drivers make informed decisions and protect their rights if faced with allegations of impairment. If you or someone you know is facing DUI charges related to marijuana impairment, it’s essential to seek legal representation from an experienced attorney who can navigate the complexities of these cases and advocate on your behalf.