Cannabis Use and Driving Impairment in Older Adults

As noted in a recently published study, though cannabis use is increasing in older adults and studies have shown that cannabis consumption increases the risk of collisions, there is a lack of studies examining the how cannabis consumption in older adults affects their driving (1). Based on this, researchers in Canada intended to study the relationship between “retail cannabis available to the consumer, driving, and associated blood tetrahydrocannabinol (THC) levels in people over 65 years of age” (1). In the introduction to their study, “Cannabis and Driving in Older Adults,” researchers also noted that THC limits are used in driving impairment tests, though there is still some debate over their effectiveness, plus the possibility of THC tolerance in older cannabis users (1). The study was published in JAMA Network Open on January 18, 2024 (1).

In this study, 31 participants, who used cannabis regularly and were between the ages of 65 and 79, operated a driving simulator before and after smoking cannabis of their choice—most cannabis samples were dominant in tetrahydrocannabinol (THC) and contained some cannabidiol (CBD) (1). Researchers tracked their speed, weaving, and reaction time and also measured THC and CBD metabolites in participants’ blood (1).

Researchers observed that weaving increased and speed decreased at 30 minutes after smoking cannabis but not after 180 minutes compared to the control conditions (1). Some of the other notable findings mentioned in the abstract also state (1):

• Blood THC levels were significantly increased at 30 minutes but not 180 minutes
• Blood THC was not correlated with SDLP [weaving] or MS [mean speed] at 30 minutes, and SDLP was not correlated with MS
• Subjective ratings remained elevated for 5 hours and participants reported that they were less willing to drive at 3 hours after smoking

The findings addressed the effects of cannabis, even a regularly used product, on driving. “The present study provides an ecologically valid demonstration that cannabis can impair driving in older adults when they smoke their usual product,” the authors concluded (1). “Consistent with emerging data, blood THC level was not correlated with driving behavior. Older drivers should refrain from using cannabis when contemplating operation of a motor vehicle.”

The study was conducted between March and November 2022 and funded by Transport Canada Enhanced Road Safety Transfer Payment Program (1).

Read more recent coverage on cannabis and older adults.

Reference

1. Di Ciano, P.; Rajji, T. K.; Hong, L.; Zhao, S.; Byrne, P.; Elzohairy, Y.; Brubacher, J. R.; McGrath, M.; Brands, B.; Chen, S.; et al. Cannabis and driving in older adults. JAMA Network Open 2024, 7 (1) DOI: 10.1001/jamanetworkopen.2023.52233.