Posted by & filed under Health Psychology, Language-Thought, Neuroscience, Physiology.

Description: With marijuana becoming legal in Canada this week (on Wednesday Oct 17, 2018) a wide array of questions (not many of them actually very new) are being asked about the effects of marijuana on human functioning and human health. If you have been in Canada you have probably seen some of the ads advising people not to “toke and drive” and while this is not a new issue, the legalization of marijuana raises the profile and perhaps adds some urgency to the question of how “impairment” due to marijuana should be define, quantified and enforced. Police have the ability to take action if a driver seems impaired for any reason (drugs, alcohol, sleep deprivation, prescription drug side effects, mental illness etc. One of the links below describes the Standard Field Sobriety Test which looks for indicators that a driver should NOT be driving. Breathalyzer testing followed by blood tests are used to determine blood alcohol levels for which there are legally defined numbers that indicate chargeable levels (.08) of alcohol in the blood and while there ARE individual differences in how people respond to that level of alcohol in their blood the law is clear and the data on the impacts of alcohol on driver performance are also fairly clear. Things are far from clear in relation to marijuana and driving. Some people claim if does not affect their driving while some even say it improves their driving. There IS a recently announced test of blood THC levels that involves roadside testing of a saliva sample but there are concerns about the reliability of the testing units (not the least of which, for Canada, that they do not work well when they are cold) and it is not clear what blood levels of TCH should be set as the legal limits for impairment. So, think a bit about what research you would want to see or to do in order to hopefully move to a defensible standard for determining if or when a driver is legally impaired by marijuana and read through the articles linked below and see if they clarify things for you.

Source: Alberta RCMP want 1 in 3 officers trained to test for cannabis impairment by 2020, CBC News: How will Canada’s new drugged-driving rules actually work? Jason Tchir, The Globe and Mail; Alcohol and Drug Impaired Driving, RCMP; Standardized Field Sobriety Test, DUI Justice Link, American Automobile Association; Even if cannabis is legal, please don’t toke and drive: U of T expert, U of T News

Date: October 12, 2018


Article Links: and and and  and finally

So, were all of your questions answered? Were any of your questions answered? Police have always had the ability to determine if, in their informed opinion using roadside sobriety testing, they should allow a driver to stay on the road. However, there are a lot of questions still about how we might define, and measure impairment based on marijuana use. With the legalization of marijuana in Canada we have an increasing need to do the research necessary to get us closer to answers to the questions of how we define and assess marijuana impairment.

Questions for Discussion:

  1. How should we define impairment by marijuana in relation to operating motor vehicles?
  2. How might we answer the question above in   relation to workplace related issues of risk and liability?
  3. What are some of the issues that potentially make these question more complicated in relation to marijuana than they have been in relation to alcohol?

References (Read Further):

Peretti‐Watel, P. (2003). Neutralization theory and the denial of risk: Some evidence from cannabis use among French adolescents. The British journal of sociology, 54(1), 21-42.

Hartman, R. L., & Huestis, M. A. (2013). Cannabis effects on driving skills. Clinical chemistry, 59(3), 478-492.

Asbridge, M., Hayden, J. A., & Cartwright, J. L. (2012). Acute cannabis consumption and motor vehicle collision risk: systematic review of observational studies and meta-analysis. Bmj, 344, e536.

Ramaekers, J. G., Kauert, G., van Ruitenbeek, P., Theunissen, E. L., Schneider, E., & Moeller, M. R. (2006). High-potency marijuana impairs executive function and inhibitory motor control. Neuropsychopharmacology, 31(10), 2296.

Papafotiou, K., Carter, J. D., & Stough, C. (2005). The relationship between performance on the standardised field sobriety tests, driving performance and the level of Δ9-tetrahydrocannabinol (THC) in blood. Forensic science international, 155(2-3), 172-178.

Battistella, G., Fornari, E., Thomas, A., Mall, J. F., Chtioui, H., Appenzeller, M., … & Giroud, C. (2013). Weed or wheel! FMRI, behavioural, and toxicological investigations of how cannabis smoking affects skills necessary for driving. PloS one, 8(1), e52545.