A suspected drug-impaired driving stop rarely produces a single roadside number that settles the question. Unlike an alcohol breath test, a Wyoming drug DUI investigation generally develops through driving observations, roadside exercises, a possible Drug Recognition Expert evaluation, and later chemical testing.
A laboratory can detect a substance without showing that it affected the person’s driving at the time of the stop. Understanding what each stage measures, and what it doesn’t, is essential when reviewing the evidence.
How a Drug DUI Investigation Begins
Police begin by looking for signs of unsafe driving and impairment, not by administering a drug breathalyzer. An officer may document lane movement, traffic violations, and the driver’s speech or coordination during the stop.
Officers often request Standardized Field Sobriety Tests, a three-part roadside battery developed through research funded by the National Highway Traffic Safety Administration. The tests are horizontal gaze nystagmus, which assesses involuntary eye movements, the walk-and-turn, and the one-leg stand. These exercises help identify impairment generally, but they don’t identify a particular drug or prove what caused the observed signs.
Trouble with a divided-attention exercise may become part of an officer’s account, but it isn’t a chemical measurement. On its own, it doesn’t establish impairment from cannabis, prescription medication, or another substance.
Why a Drug Recognition Expert May Be Requested
A Drug Recognition Expert, often called a DRE, may be called when an officer suspects impairment that a breath alcohol result doesn’t explain. The Laramie County Sheriff’s Office administers the state’s DRE program. According to the 2026 program report, Wyoming had 47 certified DREs who completed 302 evaluations in 2025.
A DRE evaluation is a standardized 12-step process rather than one standalone roadside test. It’s designed to help the evaluator determine whether observed impairment appears drug-related, alcohol-related, attributable to a medical condition, or unsupported by the observations.
The evaluation commonly includes:
- A breath alcohol test and an interview with the arresting officer.
- A preliminary examination, pulse check, eye examination, and divided-attention tests.
- Vital-sign checks, dark-room examinations, muscle-tone observations, and an injection-site check.
- Statements from the subject, the evaluator’s analysis and opinion, and toxicological testing.
The DRE may identify one or more drug categories consistent with the observations: cannabis, central nervous system depressants, central nervous system stimulants, hallucinogens, dissociative anesthetics, narcotic analgesics, or inhalants. That opinion is one part of the investigation. The toxicology results and the evaluator’s underlying observations still matter.
Blood, Urine, Breath & Other Chemical Tests
Wyoming law defines a chemical test broadly. Under Wyo. Stat. Ann. § 31-5-233, it includes analysis of breath, blood, urine, saliva, or other bodily fluids or tissues for evidence of drug or alcohol use.
Breath testing is most directly associated with alcohol. When drug intoxication is suspected, the investigation may instead involve blood, urine, or another sample submitted to a forensic laboratory for screening and confirmation. The laboratory process identifies drugs or metabolites, which are substances the body produces as it processes a drug.
This process differs from alcohol testing in an important way: there’s no regularly available handheld marijuana device that gives law enforcement a roadside concentration reading comparable to an alcohol breathalyzer. As of early 2026, no U.S. state provided officers regular access to such a device. Chemical testing identifies exposure, while the remaining evidence is used to assess claimed impairment at the time of driving.
Cannabis & Prescription Medication Cases Focus on Impairment
A positive result for THC, a prescription medication, or another psychoactive substance doesn’t end the legal analysis. Wyoming prohibits driving or having actual physical control of a vehicle while under the influence of a controlled substance, but the state has no per se THC concentration limit.
In a cannabis-related allegation, the issue is whether the person was under the influence to a degree that made safe driving impossible. Blood and urine tests can detect THC and its metabolites after the effects have worn off, so concentration alone doesn’t reliably establish recent use or impairment.
The same distinction applies beyond cannabis. A drug-related allegation can involve illegal drugs, prescription medications, over-the-counter medications, or another psychoactive substance capable of affecting physical or mental faculties. Relevant evidence includes the driving, the officer’s observations, the timing of use, any DRE evaluation, and the laboratory findings.
Chemical Test Requests & Refusals After Arrest
Wyoming’s implied consent law applies to a person driving or in actual physical control of a vehicle on a public street or highway. Under Wyo. Stat. Ann. § 31-6-102, that person is deemed to have consented to chemical testing after a DUI arrest.
When an officer has probable cause to believe the alleged impairment comes from a drug that breath testing won’t detect, the officer may require blood or urine testing rather than allow the driver to select the test type. The requested test, the stated basis for the request, and the timing of the arrest are distinct parts of the record.
A refusal can be admitted in administrative, civil, or criminal proceedings arising from the stop. Testing can also occur under a warrant or in specified serious-injury or death cases. The consequences depend on the circumstances, so a general description of Wyoming’s implied consent law can’t resolve the decision for an individual driver.
Reviewing the Evidence in a Wyoming Drug DUI Case
A drug detection result answers a different question from whether the state can prove impaired driving. The prosecution must show that a person consumed enough of a controlled substance to impair mental and physical abilities, not simply that a laboratory found a substance or metabolite.
A careful review follows the full sequence: the reason for the stop, roadside observations, field sobriety testing, any DRE procedures, sample collection, laboratory protocols, and the connection between the evidence and driving ability. Gaps or inconsistencies at one stage can affect how the overall allegation is evaluated.
R. Michael Vang holds the American Chemical Society Chemistry and the Law Division’s Forensic Lawyer-Scientist Designation, awarded in 2015. His forensic training includes evaluating methods used for field tests, blood draws, and laboratory testing.
R. Michael Vang P.C. represents people facing drugged driving allegations throughout Wyoming. For a case-specific review, contact the firm at (307) 336-7570.