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Highlights
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Use of cannabis and psychedelics continues to grow in popularity.
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More individuals report driving under the influence of cannabis and psychedelics.
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Impairments from recent cannabis use differ between occasional and daily or near-daily users.
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Evidence evaluating psychedelic use and driving impairment is currently limited, and impairment can only be inferred from existing studies evaluating cognitive and psychomotor effects.
Abstract
Use of cannabis and psychedelics continues to rise in popularity, increasing the likelihood of individuals driving under the influence. Research on psychoactive substances such as cannabis and psychedelics continues to expand, with many researchers assessing cognitive and psychomotor effects that may impact driving behaviors, while others directly measure driving-related impairments. This paper primarily reviews new studies from 2023 to mid-2025 that measure impairment after cannabis and psychedelic use, with a specific focus on studies that assess driving-related impairments. Review of the selected literature demonstrates that recent cannabis use results in different types of impairment in frequent versus infrequent cannabis users. Driving impairment studies reveal that concomitant alcohol and cannabis use likely results in additive decrements in driving performance compared to deficits seen with singular use of cannabis or alcohol. Researchers also found that combined THC/CBD products do not produce differences in driving impairment compared to THC alone. One meta-analysis concluded that blood THC concentrations do not reliably predict driving impairment. Another meta-analysis reported that low certainty evidence suggests cannabis use may increase motor vehicle collision (MVC) fatalities and related injuries. Recent investigations examining classical and atypical psychedelics cognitive impairments and appear to be dose-dependent. However, a systematic review of microdosing of LSD and psilocybin demonstrated inconclusive findings of cognitive impairment, suggesting a dose threshold for impairment. It is unknown how these findings translate into psychedelic impaired driving as no studies during the review period specifically evaluated impairment in driving after psychedelic use. The extant literature would benefit from dedicated investigations into psychedelic use and driving impairment.
Introduction
Cannabis consumption remains the most commonly used federally illicit substance in the United States. According to the National Center for Drug Abuse Statistics (NCDAS), 55 million individuals in the United States currently consume cannabis, surpassing the number of tobacco smokers in the U.S. [1]. National Roadside Surveys (NRS) conducted by the National Highway Traffic Safety Administration (NHTSA) have captured the presence of delta-9-tetrahydrocannabinol (THC) metabolites in oral fluid or blood. Between 2007 and 2014, NRS data demonstrated a 48% increase in drivers who tested positive for THC metabolites [2] however, it is unknown how many of these drivers were impaired by cannabis. The interpretation of biomarkers, such as blood THC and its metabolites, and their relationship to acute cannabis intoxication are extensive topics that fall outside the scope of this current review. However, it is well-established that the presence of THC metabolites in biological fluids does not necessarily represent impairment 3, 4, 5.
Data released by the National Institute of Drug Abuse (NIDA) and the National Institutes of Health (NIH) in 2023 showed a steep increase in psychedelic use by young adults in the U.S. over the past five years. Reported use of hallucinogens reached a prevalence of 8.9%, representing a 5.3% increase during that period [6]. As the popularity of hallucinogens, including psilocybin-containing mushrooms, lysergic acid diethylamide (LSD), 3,4-methylenedioxymethamphetamine (MDMA), and others, continues to rise, driving under the influence of hallucinogens (DUIH) has also increased. One 2021 article written by Salas-Wright et al. [7] found that 8.94% of past-year hallucinogen users reported DUIH at least once in the previous 12 months.
High-quality studies involving driving simulators and on-road driving during cannabis use consistently demonstrate that sufficient amounts of inhaled or ingested cannabis may result in impaired driving 12, 13, 14, 15, 16, 17, 18, 19. A meta-analysis performed by Asbridge et al. [20] in 2012, highlighted the risk of cannabis-impaired driving, demonstrating that acute cannabis use is associated with an increased risk of fatal motor vehicle collisions. Research evaluating functional impairments after psychedelic use remains relatively unexplored and represents a significant opportunity for future research. This review article primarily summarizes key articles from 2023 to July 2025 that identify and measure impairments after cannabis and psychedelic use.
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