Admissibility of Evidence of Drug Use in Driving Under the Influence of Drugs Cases

The number of prosecutions for driving under the influence of drugs tends to be much lower than the number of prosecutions for driving under the influence of alcohol because it is more difficult to detect and prove the involvement of drugs. Unlike alcohol, many drugs cannot be analyzed by the breath-analyzing equipment that police officers use to produce evidence. For the most part, drugs do not produce volatile products in the breath that can be analyzed to determine the presence and quantity of the drug in the blood. Furthermore, a lack of training and experience of police officers with drugs may result in the officers' inability to offer opinion testimony concerning the relationship between the presence of a drug in a subject's body and observed symptoms of intoxication.

The finding of a drug of abuse in a subject's blood or urine may result in extreme prejudice against the defendant even if evidence of impairment is not convincing. The mere presence of such a controlled substance may be enough for conviction. For this reason, many courts require probable cause for suspecting drug impairment before a sample can be taken and/or analyzed for the drug. The Drug Evaluation and Classification program (DRE) evaluation in some cases will be enough to show probable cause.

The Drug Evaluation and Classification program is a systematic approach that assesses drug impairment and the general classification(s) of the drug(s) causing the impairment. Persons who have been trained to recognize drug impairment are called drug-recognition experts (DREs) or drug recognition technicians (DRTs).

Defenses in driving under the influence of drugs cases tend to challenge the admissibility of evidence of drug use or impairment on the grounds that the evidence obtained pursuant to the DEC program is unreliable, that the officer testifying is not an expert in drug recognition, or that evidence of low drug concentration is irrelevant and prejudicial. The decision on whether to admit evidence regarding the finding of an illicit drug in a bodily fluid can be decided by balancing the probative value of the evidence with its prejudicial nature. The court strives to ensure that the value of admitting the evidence is not outweighed by any unfair prejudice and that the evidence does not confuse the issue or mislead the jury.

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