Evaluating Drugged Driving: Effects of Pain and Anxiety Medications

Gaffney, Gary R.; Brown, Timothy; Milavetz, Gary; Spurgin, Andrew · 2017 · ROSA P / Safety Research Using Simulation (SAFER-SIM) University Transportation Center

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Summary

This study investigates the impact of prescription pain and anxiety medications on driving performance, specifically examining the effects of alprazolam (a benzodiazepine) and hydrocodone/acetaminophen (an opioid) individually and in combination. Motivated by the high prevalence of prescription drug use among drivers and the known risks associated with psychoactive substances, the research aims to quantify impairment levels in a controlled environment. The study addresses a gap in understanding how these commonly co-prescribed drugs affect vehicle control, particularly regarding lateral and longitudinal stability. The researchers employed a double-blind, double-dummy, placebo-controlled crossover design with eight adult participants aged 21 to 40. Participants underwent four study visits, receiving either placebo, alprazolam (1 mg), hydrocodone/acetaminophen (10/325 mg), or a combination of both. After a 120-minute rest period post-administration, subjects completed a standardized 35-minute driving protocol on the National Advanced Driving Simulator’s MiniSim. The simulation included urban, interstate, and rural segments, with specific attention to high-speed and low-light conditions. Data collection focused on lateral control metrics, such as standard deviation of lane position (SDLP) and lane departures, and longitudinal control metrics, including speed variability and accelerator pedal usage. Subjective drowsiness was also measured using the Stanford Sleepiness Scale. Results indicated that alprazolam significantly impaired driving performance, whereas hydrocodone/acetaminophen produced only minor, non-significant deviations from placebo. Alprazolam administration led to marked degradation in lateral control, evidenced by increased SDLP and frequent lane departures, particularly during interstate curves and dark rural segments. Longitudinal control was also compromised; drivers under the influence of alprazolam exhibited greater speed variability and significantly fewer accelerator pedal adjustments, suggesting reduced active speed management. Notably, during dark straight segments, alprazolam users spent 74.2% of the time driving above the speed limit compared to 0.5% for placebo. Subjective reports confirmed that alprazolam caused significant sedation, while the opioid did not. Crucially, the combination of both drugs showed no interaction effects, indicating that the impairment was driven almost entirely by the benzodiazepine. The findings suggest that alprazolam poses a substantial risk to driving safety, particularly in challenging conditions like high speeds and low ambient light, by degrading both vehicle control and alertness. The lack of synergistic effects with hydrocodone implies that the benzodiazepine’s impact dominates the impairment profile in this combination. These results highlight the need for clinicians to counsel patients on the severe driving risks associated with short-acting benzodiazepines. The study underscores the utility of driving simulators in assessing drug-induced impairment and calls for further research into the specific cognitive and motor mechanisms underlying these deficits.

Key finding

Alprazolam significantly impaired lateral and longitudinal driving control and increased subjective sedation, whereas hydrocodone/acetaminophen had negligible effects and no interaction was observed when the drugs were combined.

Methodology

simulator

Sample size: 8

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified_with_issues.

Topics

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• prescription meds
• polydrug
• opioids
• illicit drugs
• alcohol
• anxiety depression driving

Information type

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• Empirical Findings: physiological data
• Methodological Resource: validation psychometrics, tool software