Aggressive driving consists of risky driving behaviors and traffic infractions performed with ill intent or disregard for other road users’ safety and associated with negative emotions like anger and frustration. Such behaviors may include tailgating, speeding, weaving through traffic, running red lights, and others. While evaluating the risk of drugs that decrease inhibitions or have central nervous system (CNS) stimulant effects like alcohol and cocaine for aggressive driving behaviors makes sense, doing the same with benzodiazepines and other CNS depressants may appear illogical since the drugs would have anti-aggressive effects, inducing sedation and stabilizing mood. However, unexpected aggressive/agitated episodes, albeit rarely, have been reported after the use of certain CNS depressants. The purpose of this study is to evaluate whether CNS depressants may lead to paradoxical aggressive driving behaviors by reviewing case reports of suspected impaired drivers tested positive for CNS depressants other than ethanol.

This research examined driving while intoxicated (DWI) or under the influence of drugs (DUID) cases submitted in 2019 and tested positive in blood for CNS depressants other than ethanol only (i.e., benzodiazepines, barbiturates, muscle relaxants, antipsychotics, and anticonvulsants). The blood samples were submitted by the Houston Police Department and were subsequently analyzed for alcohol and drugs by Houston Forensic Science Center and a reference laboratory. Toxicological findings, demographic information as well as driving behaviors and the standardized field sobriety test (SFST) observations of impairment described in the police reports were evaluated.

Among 1214 DWI/DUID cases in which offense occurred in 2019 and blood samples were tested positive for one or more drugs, just 50 drivers were tested positive for CNS depressants only. Twenty-five drugs/metabolites were identified with benzodiazepines/metabolites being the most prevalent, in 72% of the 50 cases. The majority exhibited typical behaviors expected from CNS depressant use: 86% of the drivers had non-violent attitudes and 91% (39/43) showed horizontal gaze nystagmus (HGN). All (n=35) showed one or more clues in Walk and Turn (WAT) and except 2, in One-leg Stand (OLS). Traffic incidents included weaving (22%), hitting an object or another vehicle (38%), stopping in a moving lane (18%). However, a few drivers exhibited agitation. Below are two case examples:

– case 1: 58-year-old female driver failed to signal a lane change, accelerating away from the patrol car and yelling. When officers encountered the driver, she exhibited uncooperative and erratic behaviors. Officer could only administer HGN, and she showed 2/6 clues. Blood sample was positive for alprazolam at 13ng/mL and meprobamate at 2.5μg/mL;

– case 2: 24-year-old female driver stopped in a moving lane of traffic. Upon officers approaching the vehicle, she began to speak to officers in an agitated voice. Officers observed the driver could not keep balance. SFST results included 4/6 HGN, 3/4 OLS, and 6/8 WAT clues. Blood sample was positive for alprazolam at 120ng/mL and for zolpidem at 100ng/mL;

Considering a multitude of social, environmental, and biological factors that can influence one's driving performance, the findings should be taken with caution and alternative interpretations other than drug effects should be considered. The research confirmed that aggressive behaviors among CNS depressant positive drivers are rare and idiosyncratic. These case examples nonetheless demonstrated how different drugged driving behaviors can be and more research is needed to further clarify the association.