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Cannabis and driving

Cannabis And Driving: Systemic Review Shows Medical Cannabis Patients Have A Different Threshold for Impairment

Patients are given little support or structure when it comes to using their cannabis and driving. The fact of the matter is, impairment isn’t the same for medical users as it is for recreational users. 

A recent systemic review took a look at existing clinical research about cannabis and impairment to try and better define what constitutes as impairment for patients. The review found that medical cannabis users generally have a different threshold for impairment than their so-called recreational counterparts, and therefore have different guidelines and testing needs.

As I have said before, when it comes to cannabis, adult-use is different from medical use. It is validating and relieving to see a comprehensive review like this affirm what patients have been saying for yearsthey don’t feel the same level of impairment as recreational consumers. 

Don’t get me wrong, I enjoy rocking a canna-buzz as much as the next person. But it isn’t a requirement of medical use; a patient could use cannabis for years and never once get stoned, and that is an important distinction. 

Further complicating the relationship between impairment and cannabis use, some patients take medical cannabis to treat impairing conditions themselves. In these cases, it is possible that cannabis could actually improve driving function.

Right now there isn’t a standardized definition of impairment associated with medical cannabis use, and thus no general consensus on how to measure or define this impairment. In the current structure there are challenges to determining this limit, including a lack of definition of impairment, testing limitations, and, as is the case with most things related to the plant, more clinical research on cannabis and driving is required.

Cannabis and Driving Impairment in Patients

Typically, patients have their own well defined parameters around driving while under the influence of a disease or its treatment. For instance, insulin dependent diabetics are only allowed to operate a vehicle if their blood sugar reads 5.0 or higher. My nurse in hospital shared the handy diddy ‘five to drive’ with me so I would remember, as legally my driving is considered impaired if my blood sugar is lower than 4.9. 

It appears no such precedent exists for medical cannabis and driving. One of the significant challenges identified in this review was defining and testing for impairment. Unlike blood alcohol levels, there isn’t a set standard of how much cannabis equals too much to drive. Establishing this threshold isn’t as simple as with other medications. 

The presence or amount of THC in the body doesn’t always correlate with neurocognitive and psychomotor function. In fact, cannabis can actually improve driving function in cases of treating certain neurological conditions, PTSD, chronic pain, and auto-immune disease that induce a certain level of neurocognitive impairment by themselves.

Patients have distinct characteristics that may modify the presence and extent of impairment. One of the review authors, Dr. Caroline MacCallum, recently told me that THC is often titrated so that patients don’t experience impairment. 

Caroline MacCullum is an author of the study on cannabis and driving.
Dr. Caroline MacCallum is one of the review’s authors.

The authors of the review on cannabis and driving also found that it wasn’t just THC that influenced neurocognitive impairment, and that other important considerations are at play. Factors like genetics, health history, dosing, method, chemovars, CBD content, tolerance, and drug interactions can influence impairment.

According to the review, recreational use of cannabis has well-established dose-dependent effects but medical cannabis effects remain a question. Patients are left to determine their own sobriety without a definitive answer on how much is too much.

So When is it Safe to Drive?

THC interacts with the CB1 receptor to impair functions like manual dexterity, coordinations, reaction time, attention span, and motor control. THC dose-dependently disrupts important cognitive and psychomotor functions needed for safety-sensitive work, including driving motorized vehicles.

While there are no hard and fast rules, recommendations have been established by the College of Family Physicians of Canada. Their 2014 statement suggests to “err on the side of caution” and delay safety sensitive activities for three to four hours if cannabis (THC) is inhaled, six to eight hours if ingested orally, and eight hours if any euphoria is experienced. 

This standard isn’t nuanced enough to account for the highly individualized effects on long-term medical cannabis patients. Determining how long a patient is impaired, and after what THC dose, proves to be challenging. In the 37 studies reviewed in the paper, there was no difference in neurocognitive measure after four hours in both THC and placebo groups. 

Generally speaking, higher doses of THC are linked to increased impairment. The review found that patients who used THC regularly developed a tolerance to the impairing effects. This doesn’t mean that patients don’t experience impairment; simply that it is more complicated than that. According to the review, regular medical consumers still showed signs of impairment, albeit blunted, following acute use.  

So how do we get to the point where doctors can confidently say, “don’t drive within x hours of taking this medication”? Medical professionals need this information so they can best advise medical cannabis patients with regards to driving or safety-sensitive tasks at work.

Cannabis and driving is a sensitive subject, and there are strong opinions on both sides. Research remains in its infancy. The effects of cannabis on humans have historically been focused more on recreational use. However the early work does show that there is a strong association between inhaled THC and acute cognitive impairment. 

Cannabis patients need to feel safe when using their physician-prescribed medications. It is difficult to feel that way when patients risk legal consequences simply because there is no framework to protect them. Regardless of personal opinions, medical patients need this information to drive confidently and safely.