What Officers Look for in a Drug Recognition Evaluation (DRE) During a Marijuana or Drug DUI Stop

When someone is arrested for driving under the influence of marijuana or other narcotics in Missouri, officers often use a Drug Recognition Evaluation (DRE) to determine whether the driver is impaired by something other than alcohol. This evaluation is a standardized, 12‑step process used by specially trained officers. Understanding what’s included in the report can help you know what prosecutors rely on—and how a defense attorney may challenge it.

1. Driver’s Appearance and Behavior

The DRE officer begins by observing the driver’s overall behavior, communication, reactions, and physical appearance. They look for things like difficulty following instructions, unusual statements, or visible signs of impairment.

2. Breath Test Results

If the driver’s breath test shows a low or zero alcohol concentration, the officer may suspect drugs and proceed with a full evaluation.

3. Questions About Drug Use and Medical Conditions

Officers ask questions about prescription medications, medical issues, sleep, injuries, and recent drug or alcohol use. These answers are documented in the report.

4. Eye Examinations

DRE officers perform several eye tests, looking for:

  • Horizontal Gaze Nystagmus (HGN) – involuntary jerking of the eye
  • Vertical Gaze Nystagmus (VGN)
  • Lack of convergence – inability of the eyes to cross properly

Certain drugs—including marijuana—can affect these results, though the reliability of these tests can be challenged.

5. Divided Attention and Coordination Tests

Just like in alcohol-related DUI cases, the officer may document standardized field sobriety tests such as the walk‑and‑turn and one‑leg stand. They note balance, coordination, and ability to follow directions.

6. Vital Signs

The officer measures:

  • Pulse
  • Temperature
  • Blood pressure

Different categories of drugs affect vital signs in different ways.

7. Pupil Measurements and Dark‑Room Tests

Using a pupil gauge and specialized lighting, the officer evaluates pupil size and reaction to light. Marijuana and many narcotics can change pupil behavior.

8. Muscle Tone Evaluation

Some drugs cause muscles to become rigid, while others cause them to become very loose. The officer documents these observations.

9. Checking for Injection Sites

Officers may look for marks or signs of recent needle use.

10. Statements and Observations

The officer documents anything the driver says or does during the evaluation, including admissions of use, confusion, or physical difficulty completing tasks.

11. Toxicology Request

At the end of the evaluation, the officer forms an opinion about what category of drug—if any—is causing impairment. They then request a blood or urine test to confirm their suspicion.

12. Final Opinion

The DRE report concludes with the officer’s final assessment of whether the driver is impaired and what type of drug may be contributing. This final opinion is often heavily challenged by defense attorneys, because DRE conclusions are subjective and not always supported by science.

Why This Matters for Your Defense

DRE reports are not infallible. Many factors—medical conditions, fatigue, anxiety, or improper testing—can affect the results. A skilled Kansas City DUI defense attorney can review the report, challenge improper procedures, and highlight weaknesses in the evaluation.

If you or a loved one is facing a DUI or DWI involving marijuana or narcotics, you don’t have to navigate it alone. My office is here to help you understand your options and protect your rights.