How Drug Recognition Experts 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.

The DRE program was first used in the 1970s by the Los Angeles Police Department but 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.

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.

Trained to Recognize Impairment

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 DECP website: "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 his 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 page outlines each individual step the DRE officer takes to examine the suspected impaired driver and make his evaluation before making an arrest for impaired driving.


Breath Alcohol Test

Young drunk driver and angry cop with breathalyser

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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 blood-alcohol concentration (BAC) level under the legal limit, the officer will then call for a drug recognition expert (DRE) officer.


Interview of the Arresting Officer

Police officer making traffic stop with female driver

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The first thing the DRE officer does is review the breath test results and then talk with the arresting officer about the circumstances surrounding the arrest, especially the officer's observations about the suspect's behavior, appearance, 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 that might indicate drug use.


Preliminary Examination and First Pulse

Police officer giving driver sobriety vision test

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The next step in the process is from the DRE officer to make a preliminary examination of the driver to determine if his behavior is being caused by an injury or a condition, rather than drugs or alcohol. The officer questions the driver about his health, diet and prescribed medications, while observing him 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.

Also during this examination, the officer takes the driver's 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 to consistency and to determine if the pulse rate is getting increasing or decreasing.


Eye Examination

Man With Crossed Eyes

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During the fourth step of the DRE protocol, the officer gives the driver tests for horizontal gaze nystagmus (HGN), vertical gaze Nystagmus (VGN) and lack of eye convergence. HGN can be caused by depressants, inhalants, and dissociative anesthetics. Higher doses of dissociative anesthetics can cause VGN. The dissociative anesthetics and marijuana can cause a lack of convergence.


Divided Attention Psychophysical Tests

Police officer taking sobriety test of man

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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 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 blood pressure, temperature and pulse (for the second time). Vital signs can be raised and lowered depending on the kind of drugs the driver is taking. Therefore, vital signs can be used as evidence to indicate drug use.


Dark Room Examinations

Dialated Pupil

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The DRE officer uses a device known as a pupilometer to determine if the driver's pupils are dilated, constricted, or normal. The officer checks the eyes for their reaction to light. Some drugs increase pupil size, other drugs lower it and some drugs cause the pupils to 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.


Check for Injection Sites and Third Pulse

Checking Pulse Rate

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Next, the Drug Recognition Expert 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 he hasn't already done so, the DRE officer reads the driver's Miranda rights and then asks him a series of direct questions regarding his 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 his 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.


Toxicological Examination

In most cases, the Drug Recognition Expert will request that the driver take a urine, blood and/or saliva test for toxicology lab analysis. The results of the test can be used as further evidence of impairment.


The International Drug Evaluation and Classification Program. "The DRE Protocol." Drug Recognition Expert.

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