A Small Pilot Trial Found No Clear Next-Day Driving Impairment After a Single THC-CBD Dose
A small randomized trial found no notable next-day impairment in cognitive, psychomotor, or simulated driving performance after adults with insomnia took a single oral dose containing 10 milligrams of THC and 200 milligrams of CBD the night before. The findings, published in 2024 in Psychopharmacology, offer limited evidence about one specific cannabis formulation and dose—not proof that cannabis is generally safe before driving.
The pilot randomized controlled trial included 20 adults with physician-diagnosed insomnia who reported infrequent cannabis use. Each participant completed two overnight laboratory visits: one involving the THC-CBD oil and another involving a matched placebo. The study used a double-blind, crossover design, so participants received both treatments in different sessions.
Researchers assessed cognitive and psychomotor performance after participants awoke and evaluated driving ability roughly 10 hours after the evening dose using a fixed-base simulator. Across 28 cognitive, psychomotor, and driving measures, 27 showed no statistically significant difference between the cannabis and placebo sessions.
One measure did show a difference: participants who received THC and CBD performed slightly less accurately on the easier, congruent portion of a Stroop test. The researchers described the reduction as small and not clinically meaningful because performance remained high overall. The simulated-driving measures—including lane control and speed-related outcomes—did not differ significantly from placebo.
The cannabis session was not entirely free of subjective effects. Participants reported feeling somewhat more sedated about 10 hours after taking the dose, although the study found no significant differences in self-rated alertness or sleepiness. That result is important because a person may feel residual effects even when standard performance tests do not show measurable impairment.
The study’s results should therefore be interpreted narrowly. It examined one dose of one oral THC-CBD product, given once, to a small group of adults who infrequently used cannabis. It did not test repeated nightly use, higher THC doses, other cannabis products, frequent users, people with conditions other than insomnia, or driving on public roads. A simulator also cannot reproduce every hazard and decision involved in real-world driving.
The findings also do not overturn broader evidence about cannabis and driving. The Centers for Disease Control and Prevention notes that cannabis can impair reaction time, coordination, judgment, and perception, while the National Highway Traffic Safety Administration advises people not to drive after using an impairing substance. In addition, people are not always reliable judges of their own impairment.
Nor does this trial establish that cannabis is an effective treatment for insomnia. Its next-day performance analysis was a secondary outcome of a larger study, and the researchers called for larger trials examining repeated dosing and higher THC exposure. For chronic insomnia, the American Academy of Sleep Medicine identifies cognitive behavioral therapy for insomnia as a first-line treatment.
In short, the study found no clear next-day cognitive or simulated-driving impairment after a single 10-milligram THC/200-milligram CBD dose in this small, carefully selected group. It does not justify assuming that all cannabis products, doses, users, or driving situations carry the same level of risk.
