How Drug Recognition Experts (DREs) Evaluate Impairment

In response to an increase in drivers who were apparently impaired but had low or no level of alcohol in their blood, law enforcement agencies across the country began using specially trained officers known as drug recognition experts or drug recognition evaluators (DRE).

With the increase in addiction to prescription drugs and the increase in the number of states legalizing medical and recreational marijuana use, the number of drivers on the highway who are under the influence of drugs increased significantly, along with the dangers of drugged driving to the public.

According to the 2018 National Survey on Drug Use and Health (NSDUH), 12.6 million people aged 16 or older drove under the influence of illicit drugs.

The DRE program was first used in the 1970s by the Los Angeles Police Department, and by the 1980s, the LAPD collaborated with the National Highway Traffic Safety Administration (NHTSA) to expand the program to other states.

Now the International Drug Evaluation and Classification (DEC) Program is coordinated by the International Association of Chiefs of Police (IACP) with support from the NHTSA.

What DRE Officers Do

A DRE officer is trained to recognize ​impairment when drivers are under the influence of drugs other than alcohol and sometimes drugs in addition to alcohol.

With the help of doctors, psychologists, and other medical professionals, the DEC program developed a multi-step program now called the DRE Protocol.

The DRE Protocol

The DRE Protocol is a 12-part examination that drug recognition experts use to determine:

  • If a suspect is impaired
  • If impairment is due to drugs or a medical condition
  • If impairment is due to drugs, which category of drugs

According to the IACP: "Nothing in or about the DRE protocol is new or novel. The DRE protocol is a compilation of tests that physicians have used for decades to identify and assess alcohol- and/or drug-induced impairment."

The DRE officer does not draw a conclusion from any one part of the evaluation, but makes an analysis based on the facts that emerge from the entire 12-part process, which is standardized as much as possible for all DRE officers everywhere.

The following outlines each individual step taken by the DRE officer to examine the suspected impaired driver and make an evaluation before making an arrest for impaired driving.


Breath Alcohol Test

Traffic police officer stopped woman for alcohol test
South_agency / Getty Images

The first step of the DRE Protocol—a breathalyzer test—is usually taken by the police officer who stopped the driver for suspicion of driving under the influence. If the suspect appears to be impaired, but has a breath alcohol concentration (BrAC) under the legal limit, the officer will then call for a drug recognition expert (DRE) officer.

If you're under 21, any detectable blood alcohol content is a violation. In 49 of 50 states and the District of Columbia, the legal limit for driving under the influence of alcohol is 0.08. In Utah, it was set at 0.05 on December 30, 2018.


Interview of the Arresting Officer

Police officer making traffic stop with female driver

RyanJLane / Getty Images 

The first thing the DRE officer does is review the BrAC test results and then talk with the arresting officer about the circumstances surrounding the arrest, especially the officer's observations about the person's behavior, appearance, and driving and if the driver made any statements regarding drug use.

The DRE officer also determines if the arresting officer discovered any other relevant evidence (such as a small pipe or a baggie) that might indicate drug use.


Preliminary Examination and First Pulse

Police officer giving driver sobriety vision test

RyanJLane / Getty Images

The next step in the process is for the DRE officer to make a preliminary examination of the driver to determine if their behavior is being caused by an injury or a condition, rather than drugs or alcohol. The officer will question the driver about their health, recent digestion of food, alcohol, drugs, and prescribed medications, while observing the driver for coordination and speech.

The DRE officer observes the driver's pupils to see if they are of equal size and determines if the eyes can follow and track equally a moving object. A tracking difference greater than 0.05 millimeters may indicate a neurological disorder, disease, or brain injury.

Also during this examination, the officer looks for horizontal gaze nystagmus (HGN) and takes their pulse for the first time. During the process, the officer will take the suspect's pulse three times to account of possible nervousness, to check for consistency, and to determine if the pulse rate is increasing or decreasing.


Eye Examination

During the fourth step of the DRE protocol, the officer examines the driver for HGN as well as vertical gaze nystagmus (VGN) and lack of eye convergence, which means their eyes are unable to converge toward the bridge of their nose when a stimulus is moved in.

HGN can be caused by depressants, inhalants, and dissociative anesthetics. Higher doses of dissociative anesthetics can cause VGN. Alcohol consumption causes distinct nystagmus in the “horizontal” or “lateral” gaze and dissociative anesthetics and marijuana can cause a lack of convergence.


Divided Attention Psychophysical Tests

Police officer taking sobriety test of man

Yellow Dog Productions / Getty Images

At this step in the DRE protocol, the officer asks the driver to take four psychophysical tests generally known as field sobriety tests. These tests, which can help determine whether a person's psychomotor and/or divided attention skills are impaired, include the Romberg Balance, the Walk and Turn, the One Leg Stand, and the Finger to Nose test.


Vital Signs and Second Pulse

Step six in the protocol calls for the DRE officer to take the driver's vital signs, including blood pressure, temperature, and pulse (for the second time). Vital signs can be used as evidence to indicate drug use, as they can be raised and lowered depending on the kind of drugs the driver is taking. For example, central nervous system (CNS) stimulants may increase heart rate and blood pressure, while CNS depressants may slow them.


Dark Room Examinations

The DRE officer uses a device known as a pupilometer to determine if the driver's pupils are normal, constricted, or dilated. The officer checks the eyes for their reaction to light.

Some drugs such as amphetamines, benzodiazepines, cocaine, crystal meth, ecstasy, and MDMA increase pupil size, while opioids (such as oxycodone, heroine, and fentanyl) cause pinpoint pupils that react slowly to light changes.

Also during this step, the officer checks the driver's nasal and oral cavities for signs of drug use (such as white powder in the nose).


Examination for Muscle Tone

Because some drugs cause the muscles of the body to become rigid and others cause muscles to become flaccid, the DRE officer checks the driver's skeletal muscle tone at step eight in the protocol. Muscle tone is often assessed by observing the driver walk and move their arms.


Check for Injection Sites and Third Pulse

Checking Pulse Rate

Image Source / Getty Images 

Next, the DRE checks the driver for drug injection sites or evidence of drug injection. At this point, the officer takes the driver's pulse for the third and final time.


Subject’s Statements and Other Observations

If they haven't already done so, the DRE officer reads the driver's Miranda rights and then asks them a series of direct questions regarding their suspected drug use.


Analysis and Opinions of the Evaluator

Drug Symptom Matrix

At this point in the process, the DRE officer forms an opinion about the driver's impairment based on the totality of the evaluation process. The officer will give their opinion ​on what category or categories of drugs the driver may be under the influence of based on the DRE Drug Symptomatology Matrix as well as the officer's personal training and experience.

DREs classify drugs in one of the following categories:

  • Central nervous system (CNS) depressants
  • CNS stimulants
  • Hallucinogens
  • Dissociative anesthetics
  • Narcotic analgesics
  • Inhalants
  • Cannabis

Toxicological Examination

In most cases, the driver will undergo a urine, blood, and/or saliva test for toxicology lab analysis. The results of the test can be used as evidence to support the DRE's opinion of driver impairment.

A Word From Verywell

Drug use while driving is on the rise and while the DREs can't prevent impaired driving, they do play an important role in the fight against drugged driving. If the DRE officer's multi-step evaluation process determines that you are indeed under the influence of drugs, you can be charged with DWI or DUI and face severe charges and penalties.

By not taking drugs, or not getting behind the wheel if you do, you can do your part to keep yourself and others safe on the road.

10 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Berning A, Compton R, Wochinger K. U.S. Department of Transportation. National Highway Traffic Safety Administration. Results of the 2013–2014 National Roadside Survey of Alcohol and Drug Use by Drivers.

  2. National Institute on Drug Abuse. Drugged Driving DrugFacts.

  3. International Association of Chiefs of Police. 12 Step Process.

  4. Governors Highway Safety Association. Alcohol Impaired Driving.

  5. National District Attorneys Association. National Traffic Law Center. The Drug Evaluation and Classification (DEC) Program.

  6. National Highway Traffic Safety Administration. Preliminary Training for Drug Evaluation and Classification Program

  7. U.S. Department of Transportation. National Highway Traffic Safety Administration. National Traffic Law Center. Horizontal Gaze Nystagmus: The Science and the Law

  8. National Institute on Drug Abuse. Health Consequences of Drug Misuse: Cardiovascular Effects.

  9. Dhingra D, Kaur S, Ram J. Illicit drugs: Effects on eyeIndian J Med Res. 2019;150(3):228-238. doi:10.4103/ijmr.IJMR_1210_17

  10. International Association of Chiefs of Police. 7 Drug Categories.

By Buddy T
Buddy T is an anonymous writer and founding member of the Online Al-Anon Outreach Committee with decades of experience writing about alcoholism.