Driving Under The Influence Of Cannabis. By Nicola Forcier

⚠️ Disclaimer: This blog reflects personal opinions and lived experience. It is not intended as medical advice. Always consult a qualified medical professional before making any decisions regarding your health or treatment options.

In Illinois, U.S.A., a driver may not operate a motor vehicle while under the influence of cannabis prescribed for medicinal purposes and may not transport medicinal cannabis in a vehicle unless it is stored in a tamper-evident container and kept in an area that is inaccessible while the vehicle is in motion. If a police officer stops a vehicle driven by a person who holds a medical cannabis registry card and the officer has reasonable suspicion to believe the person is impaired by the use of cannabis, the driver must submit to field sobriety testing. Refusal to submit to testing or failure of the field sobriety tests will result in the suspension of the person’s license. Driving while impaired by the use of cannabis, or driving with an open container, may result in the loss of driving privileges as well as the revocation of the driver’s medical cannabis card.

In randomly selected drivers throughout Europe, results showed that the most frequently detected illicit drug in traffic was cannabis.

THC had the highest rise in use during weekend nighttime hours, with 12.6% of participants testing positive for THC.

We understand how driving is often an essential tool for maintaining an active, independent lifestyle, but it is advised not to drive while intoxicated on cannabis. Initially, motor skills and judgment are impaired. In a U.S. study involving over 10,000 drivers in crashes, those who tested positive for THC were 1.25 times more likely to be involved — but due to confounding factors like alcohol consumption, increased crash risk under the influence of THC could not be definitively determined.

In Colorado (2013–2014), over 25% of road fatalities involved drugged drivers. A Canadian review of over 13,000 traffic fatalities found cannabis to be the second most common drug detected — behind depressants and ahead of narcotics. However, it is important to note that many cannabis users also consume alcohol or other substances.

A recent meta-analysis and large-scale review confirmed that cannabis is associated with impaired cognition during acute intoxication — and even lingering cognitive deficits in long-term users. Driving simulator studies consistently point to decreased attention and psychomotor function. There is substantial statistical evidence associating cannabis use with an increased risk of vehicle accidents.

Testing for cannabis intoxication is complicated. Saliva tests can yield positive results for up to a month after use. Everett’s sensitivity test showed only 38% of users tested positive in body fluid screens, making it unreliable for routine law enforcement use.

As a result, field sobriety tests remain the primary means by which officers assess cannabis-related impairment on the road.

It is safe to say that people who consume cannabis regularly should wait at least a few hours before operating a vehicle. Laws vary across jurisdictions — some enforce zero tolerance, while others allow blood THC thresholds.

What remains clear is this: cannabis impairs cognition, slows reaction time, and increases the risk of traffic accidents. Drugged driving endangers both the driver and everyone else on the road.

Stay informed. Stay safe.

— Nicola Forcier

a recent meta analysis and large review agree on association of cannabis with impaired cognition during acute intoxication and even the "clean" un-intoxicated state in long term users. Meta-analysis of experimental driving simulator studies on impaired drivers resulted in these studies pointing to attention deficit, and decreased psychomotor functioning. They also agree that there is a substantial evidence statistical association between cannabis use and increased risk of motor vehicle accidents.

There are many different ways of testing for intoxication but testing for cannabis intoxication is varied by the fact that saliva tests show cannabis positive for up to a month. Everetts sensitivity test of 38 percent which means that just 38 percent of those who consumed cannabis were detected by testing body fluids is far from sufficient for routine use by law enforcement authorities.

Field sobriety tests are often administered and are the main way for a police officer to arrest a person who may seem to be under the influence.

It is safe to say, people who consume cannabis on a regular basis should wait at least a few hours before attempting to use a motorized vehicle. In some states and countries, laws differ. Some have zero tolerance whereas some places have intoxication levels in the blood. There is absolutely much evidence to show that cannabis use impairs cognition, rate of response to an object unexpected on the road, rate of response to breaking at a changing light and many other variables all point to the fact that drugged driving is unsafe for both the driver and the general public that the person may encounter. }