Drugs and Human Performance Fact Sheets [2004]

Couper, Fiona J.; Logan, Barry K. · 2004 · ROSA P / United States. National Highway Traffic Safety Administration

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Summary

This document presents the findings of an International Consultative Panel on Drugs and Driving Impairment, convened in August 2000 and sponsored by the National Highway Traffic Safety Administration (NHTSA), the National Safety Council, and the State of Washington Traffic Safety Commission. The primary objective was to review scientific developments in drug-impaired driving over the preceding decade, identify the specific effects of various substances on driving performance, and develop practical guidance for toxicologists, law enforcement, attorneys, and the public. The report addresses the challenge of identifying impaired drivers, assessing their impairment, and interpreting chemical test results in the context of traffic safety. The panel, comprising experts in psychopharmacology, forensic toxicology, medicine, and law enforcement, selected sixteen drugs for detailed evaluation. These included over-the-counter medications (dextromethorphan, diphenhydramine), prescription drugs (carisoprodol, diazepam, zolpidem, methadone), and illicit or abused substances (cocaine, GHB, ketamine, LSD, marijuana, methamphetamine, MDMA, morphine, PCP, toluene). The methodology involved synthesizing current scientific knowledge to create uniform "Fact Sheets" for each substance. Each Fact Sheet details drug chemistry, pharmacology, dosage, routes of administration, blood and urine concentration data, psychological and physiological effects, psychomotor performance impacts, driving simulator and epidemiological studies, and Drug Recognition Evaluation (DEC) profiles. The authors note that while the sheets primarily address single-drug use, factors such as dose, tolerance, and polydrug use significantly influence impairment risks. The findings provide specific assessments for each drug. For cannabis, the report concludes that low doses moderately impair cognitive and psychomotor tasks, while high doses, chronic use, or combination with alcohol cause severe impairment. Marijuana affects perception, memory, and coordination, with effects lasting up to three hours and residual impacts potentially persisting for 24 hours. For carisoprodol and its metabolite meprobamate, single therapeutic doses are unlikely to cause significant impairment, but higher concentrations or chronic use lead to CNS depression, poor balance, and slowed reflexes. The report highlights that interpreting blood concentrations is complex; for instance, THC levels do not reliably predict impairment due to variable metabolism and tolerance, whereas meprobamate levels above 10 mg/L are associated with severe driving impairment. The Fact Sheets also outline specific DEC profiles, such as horizontal gaze nystagmus for CNS depressants and elevated pulse rates for cannabis users. The significance of this work lies in its provision of standardized, evidence-based guidance for evaluating drug-impaired driving cases. By consolidating pharmacological data with performance studies, the report aids professionals in distinguishing between mere drug presence and actual impairment. It emphasizes that impairment is task-dependent, with complex driving scenarios revealing greater deficits than simple tasks. The document serves as a critical reference for forensic interpretation, noting that urine tests often detect past use rather than current intoxication, and that blood concentration thresholds must be interpreted alongside clinical observations and individual factors like tolerance and drug interactions.

Key finding

The panel concluded that low doses of THC moderately impair cognitive and psychomotor tasks, while severe driving impairment is observed with high doses, chronic use, and in combination with low doses of alcohol.

Methodology

review

Provenance

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Topics

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• illicit drugs
• prescription meds
• opioids
• polydrug
• cannabis