Impaired driving in older adults acute 30 minutes after cannabis ingestion

Key takeaways:

• 31 older adults operated a driving simulator before and after smoking cannabis.
• Blood THC levels were significantly increased at 30 minutes but not at 180 minutes.

In a cohort of older adults who smoked cannabis, impaired driving and elevated blood THC levels were significant 30 minutes after ingestion, according to research from JAMA Network Open.

“Older adults may be particularly affected by cannabis, given age-related changes in cognition, metabolic changes that may prolong or enhance the effects of cannabis,” Patricia DiCiano, PhD, a scientist at the Institute for Mental Health Policy Research and Center for Addiction and Mental Health in Toronto, and colleagues wrote.

As cannabis has been proven to slow reflexes and its use is increasing in older adults, DiCiano and colleagues sought to examine associations between the drug, simulated driving and concurrent blood tetrahydrocannabinol levels in this population.

Their cohort study was conducted in Toronto between March 2022 and November 2022 and included 31 participants (mean age 68.7 years; 68% male) who were regular cannabis users, tasked to operate a driving simulator before, 30 minutes after and 180 minutes following ingestion of their preferred legal cannabis or after resting. Participants were recruited via telephone interviews, then screened in-person with a practice session on the simulator; those who were taken ill while using the simulator were given breaks and those who recorded persistent illness were removed from the study.

Driving acumen was assessed in both undistracted and distracted conditions. All participants were required to bring their own legally purchased cannabis and asked to smoke it as a joint with no added tobacco. Most participants chose THC-dominant cannabis with a mean content of 18.74% THC and 1.46% cannabidiol (CBD), with blood THC and metabolites of THC and CBD measured at the time of each participant’s time in the simulator.

The primary endpoint was standard deviation of lateral position (SDLP or weaving) measured in centimeters, with secondary outcomes being mean speed (MS), maximum speed, SD of speed and reaction time.

According to results, SDLP was increased and MS was decreased at 30 minutes but not 180 minutes after smoking cannabis compared with the control condition in both undistracted (SDLP effect size [ES], 0.3; b=1.65; 95% CI, 0.37-2.93; MS ES, 0.58; b=2.46; 95% CI, 3.56 to 1.36) and distracted (SDLP ES, 0.27; b=1.75; 95% CI, 0.21-3.28; MS ES, 0.47; b=3.15; 95% CI, 5.05 to 1.24) driving conditions.

Data further showed blood THC levels were significantly increased at 30 minutes but not 180 minutes, but showed no correlation with SDLP or MS at 30 minutes, while SDLP was not correlated with MS.

“Consistent with emerging data, blood THC level was not correlated with driving behavior,” DiCiano and colleagues wrote. “Older drivers should refrain from using cannabis when contemplating operation of a motor vehicle.”