A drug recognition expert is a police officer trained through the national Drug Evaluation and Classification Program to identify drivers impaired by drugs rather than alcohol, using a standardized 12-step evaluation that happens after arrest. All 50 states, the District of Columbia, and Guam participate in the program.1International Association of Chiefs of Police. States and Countries with DREs If you have been arrested for impaired driving and your breath alcohol reading is low or zero, a DRE is often the officer who decides whether the state can still charge you with driving under the influence of drugs.
Why Drug Recognition Experts Exist
A breathalyzer measures alcohol. Nothing comparable exists at the roadside for marijuana, opioids, benzodiazepines, or stimulants. An officer who stops a driver swerving between lanes may get a 0.00 breath result and still be looking at someone who is clearly impaired. The DRE program was built to fill that gap, giving officers a systematic way to document drug impairment through observable physical signs.2International Association of Chiefs of Police. The International Drug Evaluation and Classification Program
The gap is substantial. A National Highway Traffic Safety Administration study of trauma centers found that 56 percent of drivers involved in serious-injury and fatal crashes tested positive for at least one drug.3National Highway Traffic Safety Administration. Drug-Impaired Driving The DRE evaluation is a post-arrest procedure, meaning it only happens after a driver has already been taken into custody on suspicion of impaired driving.4National Highway Traffic Safety Administration. Drug Evaluation and Classification Program
The 12-Step Evaluation
Every DRE follows the same 12-step protocol, regardless of the officer or the location.5International Association of Chiefs of Police. 12 Step Process The goal is to decide three things: whether the driver is impaired, which category of drug is responsible, and whether a medical condition could explain the symptoms instead.
The evaluation opens with a breath alcohol test. If the alcohol reading doesn’t account for the impairment the officer sees, the DRE moves on. The DRE then interviews the arresting officer about what prompted the stop and the arrest, and conducts a preliminary medical examination that includes taking the suspect’s pulse for the first of three times.
An eye examination comes next, looking for three specific indicators: horizontal gaze nystagmus (involuntary jerking when the eyes track to the side), vertical gaze nystagmus (the same jerking when looking upward), and lack of convergence (inability to cross the eyes on a close object).5International Association of Chiefs of Police. 12 Step Process Different drug categories produce different eye-sign combinations, and this is one of the main ways the DRE narrows down the substance.
Four divided-attention tests follow, each designed to tax coordination and mental processing at the same time:5International Association of Chiefs of Police. 12 Step Process
- Modified Romberg Balance: standing with feet together, head tilted back, and eyes closed while estimating 30 seconds.
- Walk and Turn: walking heel-to-toe in a line, turning, and walking back.
- One Leg Stand: standing on one foot while counting aloud.
- Finger to Nose: touching the tip of the nose with an index finger, eyes closed.
Vital signs come next: blood pressure, body temperature, and pulse. These push in predictable directions depending on the drug category, with stimulants raising blood pressure and temperature and depressants lowering them. A darkroom examination then measures pupil size under controlled lighting to see how the pupils respond to light. The DRE also checks muscle tone, since some drugs produce rigidity while others leave the muscles flaccid.
Toward the end, the DRE visually checks for injection sites or other signs of ingestion, reads Miranda warnings if they weren’t already given, and asks the suspect about recent drug use. Based on everything observed across all prior steps, the DRE forms an opinion about whether the person is impaired and, if so, which category of drug is responsible. The final step is a toxicology test, usually blood or urine, sent to a lab to confirm or contradict that opinion.
The Seven Drug Categories
DREs sort substances into seven categories, each with its own fingerprint across the 12-step evaluation.6International Association of Chiefs of Police. 7 Drug Categories
- Central nervous system depressants: alcohol, benzodiazepines like Xanax and Valium, GHB, and barbiturates.
- Central nervous system stimulants: cocaine, methamphetamine, and amphetamines.
- Hallucinogens: LSD, psilocybin, peyote, and MDMA (ecstasy).
- Dissociative anesthetics: PCP and dextromethorphan.
- Narcotic analgesics: heroin, fentanyl, oxycodone, morphine, and codeine.
- Inhalants: paint thinner, gasoline, aerosol sprays, and similar substances.
- Cannabis: marijuana and synthetic cannabinoids containing THC.
Narcotic analgesics, for example, cause constricted pupils, depressed vital signs, and drowsy muscle tone. Stimulants do the opposite: dilated pupils, elevated vital signs, rigid muscles. When the pattern doesn’t fit cleanly into one category, that itself can be meaningful, and the protocol is specifically designed to flag drivers who have taken substances from more than one group.
How DRE Evidence Is Used in Court
When a driver appears impaired but blows a low or zero alcohol result, the DRE evaluation becomes the evidentiary bridge between the officer’s observations and a drug-impairment charge. The DRE’s written report documents every step of the protocol, and the toxicology result either supports or undermines the conclusion.
In court, a DRE typically testifies about the signs they observed, how those signs line up with the known effects of specific drug categories, and why they concluded the driver was impaired. What varies by jurisdiction is whether the DRE testifies as an expert witness or offers lay opinion. Under Federal Rule of Evidence 702, a witness qualifies as an expert if specialized knowledge helps the jury, the testimony is based on sufficient facts, and the methods are reliable.7Legal Information Institute. Rule 702 – Testimony by Expert Witnesses Some courts have found DREs meet that standard. Others have allowed DRE testimony only as non-expert opinion, stripping away the “expert” label and the credibility it carries.
In State v. Aleman, the New Mexico Court of Appeals found that the state had established the scientific reliability of the DRE protocol and that DREs could testify as expert witnesses about its administration and results.8FindLaw. State v. Aleman Courts in Minnesota and Massachusetts have gone the other way, requiring DRE testimony to come in as lay opinion. Some have even barred the word “expert” in front of the jury, directing that the officer be referred to as a “Drug Recognition Officer” instead.
In 2023, the New Jersey Supreme Court in State v. Olenowski set limits that signal where other courts may be headed: DREs may testify only that an evaluation is “consistent with” drug use, not that drugs actually caused impairment, and the prosecution must make a reasonable attempt to obtain a toxicology report. Without a lab result, the DRE opinion stands on much weaker ground.
Challenging a DRE’s Conclusion
Defense attorneys attack DRE testimony on two separate fronts: whether it should be admitted at all, and whether it should be believed.
Admissibility
Federal courts and most states use the Daubert standard, which asks whether the expert’s methods are scientifically reliable and relevant. Judges weigh factors like testability, peer review, known error rates, and general acceptance in the scientific community.9Library of Congress. Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 The remaining states apply the older Frye standard, which focuses on whether the method has gained “general acceptance in the particular field in which it belongs.”10Justia Law. Frye v. United States
In Frye jurisdictions, defense attorneys often argue that the DRE protocol has not gained general acceptance in the medical or scientific community because it was developed by law enforcement, not clinicians. In Daubert jurisdictions, the attack shifts to error rates. A laboratory validation study by Johns Hopkins found that when DREs concluded impairment was due to drugs other than alcohol, their opinions matched toxicology results in 44 percent of cases.11Johns Hopkins University. Laboratory Validation Study of Drug Evaluation and Classification Program Defense experts use that number to argue the protocol falls short of courtroom reliability thresholds.
Credibility
Even when DRE testimony is admitted, the weight the jury gives it can still be reduced. Common strategies include questioning the conditions in which the evaluation was conducted (poor lighting, cold weather, a nervous suspect), identifying deviations from the 12-step protocol, pointing out that DREs are police officers rather than medical professionals, and calling pharmacology or toxicology experts who testify that observation alone cannot reliably pinpoint a drug category. Inconsistencies between the DRE’s written report and courtroom testimony are another frequent target.
Your Rights During a DRE Evaluation
Because a DRE evaluation only happens after arrest, you are already in custody by the time one begins. Rules vary by state, but a few principles apply broadly.
Implied consent laws in every state require drivers arrested on suspicion of impaired driving to submit to chemical testing (breath, blood, or urine). Refusing a chemical test typically triggers automatic penalties such as license suspension, regardless of whether you are later convicted. The DRE evaluation itself is a different matter. The physical tests, eye examinations, and interview components are generally not covered by implied consent statutes, which were written to address chemical testing. In most jurisdictions, refusing to participate in those parts of the DRE evaluation is not itself a criminal act.
Refusal still has consequences. Prosecutors may point to it as circumstantial evidence of consciousness of guilt, and the DRE can still document observations made during booking and other interactions. The chemical test at step 12 (the blood or urine sample) remains subject to implied consent rules, so refusing that specific component carries the standard administrative penalties. If you are facing or anticipating a DRE evaluation, the trade-offs around cooperation are best worked through with a defense attorney before the moment arrives.