Banner for The Criminal Justice Systems: A Guide for Law Enforcement Officers and Expert Witnesses in Impaired Driving Cases

Law Enforcement Testimony


In many jurisdictions, the DRE (Drug Recognition Evaluator/Expert) may be put forth as a “technical” expert, one with specialized knowledge whose testimony is based on observation, education, training, skill, and experience.3 The DRE is not a doctor, pharmacologist, or toxicologist. Nonetheless, the DRE has specialized knowledge that will assist the trier-of-fact to understand the evidence. Just as an individual does not have to understand how a television works in order to determine that the set is working, the DRE does not need to know the scientific explanation of how drugs cause impairment to recognize impairment.  Prosecutors handling drug-impaired-driving cases will find DRE testimony particularly helpful. For further details, see The Drug Evaluation and Classification (DEC) Program available for downloading at

In a typical alcohol-impaired-driving case, an officer may testify to many indicators of alcohol impairment observed during the investigation. The officer’s testimony is based on observation, training, and experience in detecting impaired drivers even though the signs of impairment are based on scientific principles.

A driving under the influence of drugs (DWID) case comes before the court in the same manner as an alcohol-impaired-driving case. The arresting officer either comes upon an incident or makes a traffic stop because there is a traffic violation or reasonable suspicion to believe that the suspect is driving under the influence of an intoxicating substance. The initial investigation is conducted as any other impaired-driving case. Observations of impairment are made by the arresting officer in the course of the investigation.

The DRE usually becomes involved after the suspect takes a breath test and the results are inconsistant with the impairment the arresting officer observed. For example, the suspect was driving erratically and performed the SFSTs poorly but the breath test result is .02 BAC. Sometimes the arresting officer may suspect drug impairment at the outset from observations of drugs or drug paraphernalia on the suspect or in the car, with or without a subsequent breath test. And, sometimes the defendant volunteers that he has consumed something other than or in addition to alcohol. That admission, without more, is generally not enough to convict for drug-impaired driving.

The DRE is called in for three distinct purposes:  First, the DRE establishes that the suspect’s impairment is caused by a drug or drugs other than or in addition to alcohol, and rules out a medical condition or medical emergency.

Second, the DRE identifies and notes the category of drug consumed by the suspect, which is helpful to the toxicology laboratory in determining which substances to test for. The DRE does not identify a specific drug, such as cocaine, but rather the general category of drugs (e.g., in the case of cocaine, a central nervous system stimulant). Just as the officer is not required to determine the type of alcohol or the brand of beer a suspect consumed in order to offer an opinion that an individual is driving under the influence of alcohol, the DRE is not required to identify the specific drug.

Third, at trial, the DRE will testify to all the signs and symptoms of impairment he or she observed and may be allowed to offer an opinion that the impairment is consistent with the drugs verified by the chemical test. Regardless of whether the DRE is allowed to offer such an opinion, the prosecutor will likely call on a toxicologist to further explain the connection between the signs of impairment observed by the DRE and the drug found by the toxicology lab.

In the drugged-driving case, at least one obvious factor is whether a drug or combination of drugs caused the impairment. Therefore, testimony on the signs and symptoms of drug impairment is critical to the fact finder’s ability to determine (1) the person was impaired and (2) the impairment was the result of a substance other than, or in addition to, alcohol.

At trial, the prosecutor will ask about your general training and experience as a police officer prior to becoming a DRE. For example:

  • Assignments related to drug enforcement as a narcotics officer
  • Selection process for the traffic/DWI enforcement division
  • Length of time assigned to traffic/DWI enforcement
  • Specialized training for traffic/DWI enforcement
  • Special recognition for work in DWI enforcement

You will be asked to discuss, if applicable:

  • Training as an emergency medical technician, paramedic, or medical corpsman in the military; and/or
  • Employment as a security officer in a jail, as a probation officer, or in a drug rehabilitation facility.

Finally, questions will concentrate on the education and training necessary to become a DRE officer. Questions may include the following:

  • How were you selected for the program?
  • How many other officers from the department were selected for DRE training?
  • What does the pre-school involve?
  • Does everyone who attends the pre-school become a DRE?
  • How long is DRE school?
  • How did you learn to take vital signs and who checked for accuracy?
  • How many evaluations did you participate in as a student?
  • Were these evaluations supervised?
  • Is there a separate certification process after completion of the classroom work? 4
  • What is involved in becoming certified?
  • Are you certified?
  • By whom?
  • Are you required to renew DRE certification?
  • How often?

If you are a new or somewhat inexperienced DRE, the focus of the questions may be education and training, and perhaps your previous jobs and responsibilities, if applicable. If you are a more experienced officer, emphasis will likely be placed on actual skills and experience:

  • How many times have you performed a drug influence evaluation?
  • Were your results consistent with toxicology testing? (Explain)
  • Do you arrest everyone for whom an evaluation was performed?

The manner in which you testify—the words you choose to convey the information and your courtroom decorum—will follow closely the discussion as outlined above for officers testifying about Standardized Field Sobriety Tests.


Prior to trial, be sure to discuss your conclusions with the arresting officer(s), the toxicologist, and the prosecutor. This is not for the purpose of “matching testimony” but rather to ensure that any unanswered questions or potential discrepancies are addressed beforehand.


3 Drug Evaluation and Classification (DEC) is the State program, while a DRE is an officer that is a part of the DEC program.

4 As a condition of DRE certification, the DRE must submit and maintain a resume (or a curriculum vitae) that documents the DRE’s experience. Have this available for the prosecutor both prior to and at trial