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Addressing cannabis-impaired driving: International researchers join forces to help inform policy and legislation globally

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Ottawa, ON August 31, 2022 – (GLOBE NEWSWIRE) – The International Council on Alcohol, Drugs & Traffic Safety (ICADTS) has released new tools summarizing the latest research about cannabis-impaired driving to help inform policymakers across countries. This series of fact sheets were developed in consultation with leading impaired driving researchers from 11 countries representing ICADTS Drugged Driving Work Group.








Co-chaired by Maastricht University (Netherlands), the Traffic Injury Research Foundation (TIRF/Canada) and Swinburne University of Technology (Australia), this work group aimed to answer top questions commonly raised by policymakers around the globe. This fact sheet series interprets critical research findings regarding several facets of the problem and their implications for policy and legislation. The purpose is to clarify important research findings to help ensure the development and implementation of cannabis-impaired driving policy and legislation are appropriate and informed by science.








As of 2022, many countries have legalized recreational and/or medical cannabis use including Canada, Georgia, Malta, Mexico, South Africa, and Uruguay. In the United States, cannabis is legal in 19 states, 2 territories, and the District of Columbia. Many more jurisdictions, such as Germany, are contemplating such a move and this global trend is likely to continue.

“Unlike alcohol, the research regarding the impairing effects of Δ9 tetrahydrocannabinol (THC; the active ingredient of cannabis) on driving is much more complex because cannabis does not have a clear concentration-effect response,” shares Jan Ramaekers, Professor, Maastricht University and former ICADTS president. “This means it’s difficult to conclude whether a specific THC concentration is indicative of driving impairment in an individual, making policy decisions much more complex.”

To date, jurisdictions have adopted a variety of legal approaches to tackle the impaired driving problem. Whereas some jurisdictions have opted for zero-tolerance laws, others have relied on behavioural measures of impairment, and still others have instead implemented specific per se limits in law. This latter approach is more consistent with existing alcohol-impaired driving laws. The application of these laws is further impacted by whether recreational and/or medical cannabis use is deemed to be legal or not.

“With alcohol, a blood alcohol concentration (BAC) accurately reflects the amount of alcohol consumed. Despite some variations between subjects, research shows as BAC rises, so does the level of impairment,” says Robyn Robertson, President & CEO, TIRF. “However, THC concentrations do not accurately reflect the amount of cannabis consumed or the level of impairment of individual drivers, so determinations of impairment are much more complex and less clear cut. As such, it’s critical for legislators to recognize important limitations of the science to ensure laws are appropriate and enforceable.”

Some of the most important facts for policymakers to be aware of, include:

  • Cannabis impairs driving, although the degree of impairment it produces varies substantially depending on the dose, the individual, and other factors.
  • Cannabis, when consumed alone, is associated with a modest increase in crash risk at the population level according to most studies which compared the presence versus the absence of cannabis.
  • A driver testing positive for THC is insufficient to conclude driving impairment. Any impairment is dependent on not only the dose and route of administration but also the frequency of use and whether cannabis has been consumed alone or in combination with alcohol or other substances.
  • Alcohol and cannabis produce different patterns of impairing effects.
  • The combined effect of alcohol, even in low concentrations, and cannabis is particularly dangerous for driving.
  • The length of time needed to recover from cannabis intoxication is not fixed and depends on various factors, such as biological characteristics of consumers, type of cannabis consumed, dose, and method of ingestion.

Many jurisdictions have implemented a multi-faceted approach to detecting and measuring impairment. Important tools include oral fluid devices, behavioural assessments such as the Drug Recognition Expert (DRE) program which is widespread in Canada and the US, and robust standards to guide the toxicological analysis of body fluids and the interpretation of results.

“When it comes to cannabis, there is very little consistency in how jurisdictions manage the issue of impaired driving,” notes Thomas Arkell, Research Fellow, Swinburne University of Technology. “A priority moving forward is establishing greater uniformity in the types of tools used to assess impairment and the way in which results are recorded. This would allow us to pool data from different jurisdictions and better assess the impact of expanding legalization on traffic safety. It would also help accelerate learning to enable researchers to provide clearer answers to policymakers on important legislative issues.”

Download the Cannabis & Driving fact sheet series:

About The International Council on Alcohol, Drugs & Traffic Safety (ICADTS):
ICADTS is an independent not-for-profit body whose only goal is to reduce mortality and morbidity brought about by misuse of alcohol and drugs by operators of vehicles in all modes of transport. To accomplish this goal, the Council sponsors international and regional conferences to collect, disseminate and share essential information among professionals in the fields of law, medicine, public health, economics, law enforcement, public information and education, human factors and public policy.

About TIRF
The vision of the Traffic Injury Research Foundation (TIRF) is to ensure people using roads make it home safely every day by eliminating road deaths, serious injuries and their social costs. TIRF’s mission is to be the knowledge source for safe road users and a world leader in research, program and policy development, evaluation, and knowledge transfer. TIRF is a registered charity and depends on grants, awards, and donations to provide services for the public. Visit

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