Cannabidiol (CBD) is a compound derived from the hemp or cannabis plant. Unlike tetrahydrocannabinol (THC), CBD is not intoxicating and does not produce the “high” associated with cannabis use. The widespread availability of CBD products raises a significant question: Does using this compound affect the ability to operate a motor vehicle safely? Understanding the science behind CBD’s effects is necessary to determine its risk to driving performance. The primary concern is whether CBD, even without intoxication, can impair the complex cognitive and motor functions required for safe driving.
The Difference Between CBD and THC
The fundamental difference between CBD and THC lies in how each compound interacts with the body’s endocannabinoid system (ECS). The ECS is a network of receptors and signaling molecules that helps regulate various functions, including mood, memory, and coordination. THC exerts its psychoactive effects by binding directly to the cannabinoid 1 (CB1) receptors, which are concentrated in the central nervous system. This activation disrupts normal neurological processes, leading to euphoria, altered perception of time, and impaired motor control, all detrimental to driving.
In contrast, CBD has a very low affinity for the CB1 receptor and does not bind to it directly like THC. Instead, CBD is thought to modulate or indirectly influence the CB1 receptors. It also interacts with other non-cannabinoid receptors, such as serotonin receptors, which may explain its therapeutic effects. This non-psychoactive mechanism is why CBD does not cause the intoxication or impairment characteristic of THC.
Scientific Findings on CBD and Driving Performance
Scientific studies, including those using driving simulators and real-world on-road tests, have investigated CBD’s impact on driving metrics. Researchers focus on objective measures such as the standard deviation of lateral position (SDLP), a measure of weaving and vehicle control. Multiple studies have consistently shown that pure CBD, even at high doses up to 1500 milligrams, does not cause significant impairment in driving performance. For example, one study involving high-dose oral CBD found no statistically significant changes in simulated driving performance compared to a placebo.
In real-world conditions, a landmark study assessed drivers after consuming vaporized cannabis that was CBD-dominant, THC-dominant, or a combination. The study found that products containing mainly CBD did not affect the participants’ ability to drive safely. Key indicators of impaired driving, such as reaction time, visual function, and lane-keeping ability, remained largely unaffected by the consumption of CBD alone. The overall body of evidence suggests pure CBD does not compromise the cognitive function or motor control necessary for driving.
Legal Considerations Regarding CBD Use and Driving
The legal vulnerability for a CBD user stems from drug-driving laws that frequently center on the presence of THC. Many jurisdictions enforce per se laws, meaning a driver can be charged with driving under the influence (DUI) if their blood contains THC or its metabolites above a specific concentration limit. This is distinct from impairment laws, which require proof that the driver’s ability was diminished. Since most CBD products are derived from hemp, they are federally required to contain less than 0.3% THC.
However, using full-spectrum CBD products, which contain trace amounts of THC, can lead to the accumulation of THC metabolites in the body over time. This accumulation, even without any psychoactive effect, can result in a positive drug test that meets the threshold for a per se DUI violation. The law often struggles to differentiate between recent, impairing THC use and residual, non-impairing THC metabolites from legal CBD use. Therefore, a driver who is unimpaired by CBD may still face legal consequences due to a positive test for trace THC.
Factors Influencing Potential Impairment
Although pure CBD is generally considered non-impairing, several factors can introduce a risk of diminished driving ability. One factor is the product type, particularly the difference between full-spectrum, broad-spectrum, and isolate products. Full-spectrum products contain all cannabinoids, including trace THC that poses a legal and potential impairment risk. Isolates, which contain only pure CBD, eliminate the THC risk.
Another factor is the combination of CBD with other central nervous system depressants, which can lead to additive sedative effects. CBD can interact with medications like sedating antidepressants, opioids, alcohol, and benzodiazepines, potentially increasing drowsiness or fatigue. This interaction occurs because CBD can inhibit certain liver enzymes, such as Cytochrome P450 enzymes, which metabolize many common drugs. By slowing the breakdown of these medications, CBD can increase their concentration in the body, resulting in unexpected sedation that could impair driving ability.