A drug recognition expert evaluation is a structured 12-step examination performed by a police officer with specialized training, used to determine whether a driver is impaired by drugs when a breath alcohol test comes back low or clean. The officer, known as a Drug Recognition Expert (DRE), works through physical checks, eye tests, vital signs, and an interview to decide whether you are impaired and, if so, which of seven drug categories is responsible. The program operates in all 50 states, the District of Columbia, and Guam.1International Association of Chiefs of Police. States and Countries with DREs
What Happens During the Evaluation
A DRE is usually called in after another officer has already arrested a driver and a breath test has ruled out or minimized alcohol as the cause of impairment. The evaluation itself follows a fixed sequence of 12 steps, and each step is meant to add another piece of evidence to a cumulative picture.2International Association of Chiefs of Police. 12 Step Process
- Review of the breath alcohol test result to confirm alcohol doesn’t explain the impairment.
- Interview with the arresting officer about driving, behavior, and appearance.
- A preliminary examination to rule out a medical cause, and the first of three pulse readings.
- Eye examinations checking for horizontal gaze nystagmus, vertical gaze nystagmus, and lack of convergence when the eyes try to cross on a close object.
- Four divided attention tests: Modified Romberg Balance, Walk and Turn, One Leg Stand, and Finger to Nose.
- Blood pressure, body temperature, and a second pulse reading.
- Dark room pupil measurements under three lighting conditions using a pupilometer.
- A check of skeletal muscle tone for rigidity or flaccidity.
- Inspection for injection sites and a third pulse reading.
- An interview with the subject about drug use.
- The DRE’s formal opinion on whether the subject is impaired and by which drug category.
- Collection of a blood or urine sample for toxicology.
The three pulse readings are taken at different points on purpose. Rates rise and fall with anxiety, environment, and the drug wearing off, so multiple readings give a more reliable baseline than one snapshot.
The Seven Drug Categories
A DRE isn’t trying to name the exact substance you took. The goal is to match the pattern of physical signs to one of seven categories, each with a recognizable signature across the 12 steps:3International Association of Chiefs of Police. 7 Drug Categories
- CNS depressants (benzodiazepines, barbiturates): sluggish pupil reaction, low blood pressure, flaccid muscle tone.
- CNS stimulants (cocaine, methamphetamine): dilated pupils, elevated pulse and blood pressure, raised body temperature.
- Hallucinogens (LSD, psilocybin): dilated pupils with normal light reaction, elevated pulse and blood pressure.
- Dissociative anesthetics (PCP, ketamine): horizontal and sometimes vertical nystagmus, normal pupil size, rigid muscle tone.
- Narcotic analgesics (heroin, oxycodone, morphine): constricted pupils, low pulse and blood pressure, flaccid muscle tone.
- Inhalants (paint thinner, aerosols): nystagmus, slow pupil reaction, possible chemical odor.
- Cannabis: lack of eye convergence, elevated pulse, possible pupil dilation, no nystagmus.
Constricted pupils, low pulse, and drowsy muscle tone point toward opioids. Dilated pupils, fast pulse, and rigid muscles point toward stimulants. The DRE reads the whole pattern rather than any single sign.
Polydrug cases complicate this. IACP data from 2018 to 2022 shows roughly 41 percent of all DRE evaluations involved multiple drugs or substances, and overlapping effects can mask or amplify individual drug signatures.4International Association of Chiefs of Police. Including Any Impairing Substance or Drug in Driving Under the Influence of Drugs (DUID) Statutes
What You Can Refuse and What You Can’t
The evaluation mixes two very different legal categories, and the difference decides what a refusal costs you.
The physical portions of the evaluation, meaning the eye exams, divided attention tests, vital signs, pupil measurements, and muscle tone checks, are generally treated the same way as standard field sobriety tests. Drivers are not legally required to perform them, and declining these steps does not typically trigger the automatic penalties that come with refusing a chemical test.
The toxicology sample at step 12 is different. Implied consent laws in every state require drivers to submit to chemical tests, meaning breath, blood, or urine, when lawfully arrested on suspicion of impaired driving. Refusing that sample triggers automatic administrative penalties like license suspension, whether or not you were actually impaired.
Refusal of the physical portions isn’t consequence-free either. The officer will document it, and prosecutors can point to it at trial as evidence of consciousness of guilt. So the practical picture: you can generally decline the physical steps, but the blood or urine draw at the end has real legal teeth.
How Accurate the Evaluation Is
NHTSA-funded validation studies have tested DRE performance under controlled conditions. One key study found an overall accuracy rate of 94.8 percent, a 95.3 percent sensitivity rate for correctly identifying that a subject was on drugs, and a 2.0 percent false positive rate for wrongly flagging a sober subject. Identifying the correct drug category is harder: specificity was 80.0 percent overall, and depressants had a notably higher miss rate of 43.2 percent. Stimulants and narcotic analgesics were identified most reliably.
Other researchers have found similar numbers. One study reported toxicology confirmed the DRE’s category opinion 83.5 percent of the time. Another found 98.7 percent sensitivity and 91.7 percent specificity. Strong enough to support the program’s use, imperfect enough to leave real room to contest an individual evaluation.
How the Evaluation Is Used in Court
If the DRE concludes you are impaired, the evaluation becomes part of the evidence package in your criminal case. The written report documents every measurement and observation from the 12 steps and goes to prosecutors, and is discoverable by the defense. The toxicology sample is sent to a lab, and results can take weeks or months to return.
DREs regularly testify as expert witnesses. To qualify, the officer must demonstrate specialized knowledge, skill, experience, training, or education that helps the jury understand evidence it couldn’t evaluate on its own, and the testimony must rest on sufficient facts, reliable methods, and a reliable application of those methods to the case.5Legal Information Institute. Federal Rules of Evidence Rule 702 – Testimony by Expert Witnesses Federal courts and many state courts apply the Daubert standard, which asks whether the method can be tested, has been peer-reviewed, has a known error rate, follows maintained standards, and is widely accepted in its field. Other states use the older Frye standard, which just asks whether the method is generally accepted by experts. DRE testimony has been admitted under both.
Where the Evaluation Gets Challenged
The strongest defense arguments usually target the specific evaluation rather than the program as a whole. Common attack points include:
- A mismatch between the DRE’s predicted category and what the toxicology report actually found.
- Failure to complete all 12 steps or follow the protocol correctly.
- The DRE’s inexperience or a low personal evaluation count.
- Medical conditions that could produce the same signs the DRE attributed to drugs.
A DRE who predicts stimulant impairment when the blood test comes back positive only for cannabis has handed the defense a discrepancy that can undermine the whole evaluation in front of a jury. If you’re facing charges built on a DRE evaluation, the toxicology report and the officer’s written documentation of each of the 12 steps are the two pieces of evidence to review with a defense attorney first.