As marijuana legalisation continues to expand across the United States, a growing concern has emerged regarding marijuana-impaired driving. Despite widespread legalisation, with 38 states approving medical use and 23 allowing recreational use as of April 2023, the challenge of addressing marijuana-impaired driving remains significant. Unlike alcohol, which has established metrics for impairment, determining marijuana’s effects on driving presents complex challenges.

Legal Landscape and Challenges

The legal framework for marijuana-impaired driving varies across states, with differing approaches to regulating THC levels—the psychoactive component in marijuana. Some states, like Ohio and Illinois, have set specific THC limits for driving, ranging between 2 and 5 nanograms per millilitre of blood. However, the effectiveness of these limits as indicators of impairment is under debate. In other states, zero tolerance laws prohibit any detectable THC level while driving.

Efforts to develop reliable testing methods for THC impairment, such as breathalysers, have been largely unsuccessful. THC’s complex behaviour in the body, coupled with its larger molecular structure compared to alcohol, complicates the creation of effective, consistent tests. Currently, blood and saliva tests are the primary methods used, though their reliability is questioned.

Public Health Implications

Marijuana is the most commonly used federally illegal drug in the U.S., with 48.2 million users in 2019, highlighting the urgent need to address marijuana-impaired driving. Researchers note that public awareness of marijuana’s potential driving hazards is lower compared to alcohol, despite evidence showing similar risks. Marijuana affects cognitive functions unpredictably, acting as a depressant, stimulant, or hallucinogen, which complicates efforts to establish clear impairment thresholds.

Statistics on Marijuana Use and Driving

The prevalence of marijuana use among drivers has increased significantly over recent years. According to toxicology reports from fatal car crashes, the number of drivers under the influence of marijuana has multiplied five to tenfold since 2000. A 2022 National Transportation Safety Board report identified marijuana and alcohol as the most detected substances among impaired drivers. Moreover, many drivers who tested positive for marijuana also had other impairing substances in their system.

Comparison with Alcohol Impairment

Unlike alcohol, where impairment levels are well-understood and regulated, marijuana’s effects on driving remain elusive. Dr. Guohua Li, an expert in epidemiology, underscores that marijuana’s impact on driving is more unpredictable than alcohol. While alcohol functions predominantly as a depressant, marijuana can affect the central nervous system in various ways, making consistent impairment measurements difficult.

Ongoing Research Efforts

Research continues to explore the relationship between marijuana use and driving impairment. A study published in JAMA Network Open highlighted a 475% increase in cannabis-related traffic injuries in Ontario, Canada, from 2010 to 2021. Although cannabis-involved traffic injuries represent a small fraction of total traffic injuries, this trend underscores the growing concern over marijuana-impaired driving.

Efforts to determine reliable THC impairment indicators remain ongoing. Current studies suggest that THC levels in bodily fluids are not reliable markers of impairment. The need for comprehensive research on marijuana’s impact on driving and the development of accurate testing methods is critical as legalisation spreads.

Source: The Mandarin