Driving under the influence of cannabis

Attitudes toward driving under the influence of cannabis vary greatly. Some individuals claim that driving under the influence is extremely dangerous; whereas others suggest that cannabis is a fairly innocuous substance that does not increase your risk of collisions.  Research indicates that the true answer is somewhere between these two extremes. Comparisons between studies of alcohol intoxication and collision risk versus studies of cannabis intoxication and collision risk show that alcohol has more detrimental effects on driving than cannabis has on driving. Conversely, some research has shown that drivers under the influence of high levels of cannabis attempt to compensate for their condition by driving slowly and cautiously. However, while compensation can help reduce the risks of collision, these risks are not fully eliminated.

A recent review of the evidence showed that cannabis doubled the likelihood of a collision, which would be similar to the likelihood of collision from having a blood alcohol content (BAC) of .05%, the legal alcohol limit in most Canadian provinces.  For comparison, heavy alcohol intoxication to a BAC of .20% alcohol is related to over an 80 fold increased likelihood of a collision. Cannabis affects your attention span making it harder to concentrate on driving and makes it difficult to shift attention to deal with changes in the environment. Evidence suggests cannabis may also impair tracking ability (i.e., harder to follow your lane), and sense of time and distance.  The duration of impairment from cannabis lasts on average about 90 minutes, but it is best not to drive within 4 hours after smoking cannabis.

It is a criminal offense to drive under the influence of cannabis, however, nearly half a million Canadians admitted to driving within two hours of using marijuana or hashish in 2006 and youth report driving after cannabis more than after alcohol (40% vs. 20%). If a police officer suspects that you are driving while under the influence of cannabis, you can be sent to the police station for examination of impairment by a drug recognition expert, and possibly be asked to provide a biological specimen, such as urine or blood for analysis. This process is time consuming and cumbersome for the police. Some countries have dealt with the issue by implementing roadside saliva testing – a test that can detect the use of cannabis over the past few days. For example, Australia has a zero tolerance policy for driving under the influence of cannabis and uses roadside saliva tests to assess for the presence of THC. However, saliva and urine tests are not as effective at detecting impairment compared with the Breathalyzer test used for alcohol, where increased blood alcohol concentration corresponds closely with safety risk. That is, a person who tests positive for cannabis on a saliva or urine test may not be under the influence at the time of the test and therefore their driving may not be impaired. Another more accurate option for detecting cannabis impairment is the use of blood tests, currently being used in Germany, however these tests are also more intrusive and difficult to implement at roadside.

Driving under the influence of cannabis is a serious public health concern and with the recent legalization of cannabis in Washington State and Colorado and the continued movement towards decriminalization of cannabis in BC, cannabis related driving policies will be an important component of any regulatory system. 

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Authors: Scott MacDonald, Assistant Director, CARBC, and Chantele Joordens, Research Associate, CARBC


A look at cannabis legalization in Colorado, USA

It has been over forty years since the Nixon administration declared a “war on drugs”; the criminalization of drugs still reverberates throughout all corners of America today. Yet last November voters said “yes” on legislation that ended marijuana prohibition in not one but two states. Come January 2014, Washington and Colorado will allow adults 21 years and older to use, manufacture and sell cannabis in a manner similar to alcohol or tobacco. In a nation that charges over 1.5 million people per year for drug violations, how did such a shift happen?

Let’s back up to November 2000 when Colorado passed its first medical marijuana legislation, Amendment 20, which initiated what has become the most successful and sophisticated medical marijuana industry in U.S. history. With more medical marijuana shops than liquor stores or Starbucks outlets, the industry has created an infrastructure and attitude that has changed the way Coloradans think about pot.

This important shift in mentality has moved the conversation from drug criminalization to profitability and regulation. The medical marijuana industry proved that big bucks were being made in the state of Colorado – what has since been termed the “Green Rush.” According to the State of Colorado website, medical marijuana sales were over $200 million, generating over $5 million in state sales tax. Evidence like this caused activists to project and campaign a $600 million profit margin per year – a profitability that the majority of Coloradan voters wanted.

Unfortunately, though, you can’t just say “marijuana is legal” and expect things to sort themselves out. Over the past year, activists, lawyers and politicians of Colorado’s Amendment 64 campaign have been putting out fires and doing everything necessary to smoothly implement the new state law.

The biggest post-legalization concerns surround children, driving and taxation. According to the Denver Post, from 2005 to 2009, Children’s Hospital Colorado had virtually zero emergency room visits from pediatric marijuana ingestions. When conversation of legalization began in 2010, there were 14 emergency room visits. That same year, poison centre calls from pediatric marijuana ingestions doubled. Since then, regulators have been working to create safety measures that can prevent such exposures, including childproof packaging that could be required for all cannabis products in the state come the new year.

Regulators have also been working hard to devise safeguards on our roads.  Unlike alcohol, there is no clear-cut consensus on the amount of marijuana that would impair a driver’s ability. Marijuana users could have tetrahydrocannabinol (THC) in their body for up to a week or more after lighting up, making it difficult to assess the driver. Since Amendment 64 passed, a new law has set a THC of 5 or more nanograms per millilitre to be considered illegal. However, even with the new standard, skeptics are expecting numerous defendants and court cases to emerge as the law becomes implemented.

The last and most recently debated step in the legalization process has been to establish state revenue goals and taxation laws. On November 6, 2013, voters overwhelmingly approved Proposition AA, authorizing a 15% excise tax and special sales tax of up to 15%.  Adding this to county sales taxes as high as 15%, this makes pot one of the most heavily taxed consumer products in Colorado – higher than alcohol even without taking local levies into account.

A recent Forbes article argued that with taxes that high, there is serious concern that legal marijuana may have trouble competing with the black market.  BOTEC analysis corporation report estimates that a legal ounce of weed will cost anywhere from $482 to $723 – much higher than the estimated black market price of $238. If those price comparisons are the actual prices, Colorado may be perpetuating instead of eliminating illegal cannabis, undermining Amendment 64 altogether.

Come January 1st, Colorado is open for business and the world is watching. Colorado and Washington alike will serve as important examples of what marijuana legalization should or should not look like. If legalization is successful, other states, provinces or countries may follow suit. If it is not, legalization could risk pushing drug policy back and perpetuating the black market and criminalization even further.

Using Colorado’s road to legalization as an example, do you think B.C. is ready?

*Please note that the material presented here does not necessarily imply endorsement or agreement by individuals at the Centre for Addictions Research of BC


Author: Alissa Greer, Research Project Coordinator at Rocky Mountain Poison and Drug Center