Last month, Bill C-45, also known as the Cannabis Act, passed its second reading in the House of Commons — the culmination of several days and late nights of debate among members of Parliament about the proposed framework for legalized cannabis.

‘Perplexing’ might be a good word to describe many of the arguments made in the House. Some were obscure to the point of entertainment (just look up #toasterbud), but others were disconcerting for those of us researching cannabis and public health.

While it’s hard to resist the amusement of watching our elected representatives engage each other in a serious debate using words like “doobie” and “reefer” — and predicting that children will use toaster ovens to dry out and smoke homegrown cannabis, for every embarrassing cannabis pun or laughably far-fetched “what-if” scenario, there were just as many unchecked scientific-sounding claims about the public health impacts of cannabis policy.

But to what extent are these claims rooted in reality? MPs are not required to cite supporting sources of evidence in House debates, often preventing the public from critically analyzing the validity of their statements.

So we set out to unpack three of the most common claims heard in House of Commons about the health and social impacts of cannabis legalization in other jurisdictions — and test them against current scientific evidence.

Claim #1: Legalization has led to increased rates of cannabis use among youth in Colorado and Washington

The governing Liberal MPs have been tireless in emphasizing that youth are at the center of their plan to legalize cannabis. Noting that Canada’s youth lead the world’s richest nations in rates of cannabis use, supporters of the bill have pointed to the failings of prohibition, arguing that regulating and restricting access to cannabis will “keep it out of the hands of children”.

The opposition Conservatives have never missed an opportunity to claim that this legislation — which allows up to four cannabis plants per household and protects youth from harsh criminal penalties for simple possession of five grams or less — will encourage use among Canada’s youth. Several Conservative MPs cite Colorado and Washington as examples to demonstrate that legalization will lead to escalating youth cannabis use. But did youth usage really increase in these states after legalization?

Let’s look at Colorado. The Rocky Mountain High Intensity Trafficking Area provides annual reports for Colorado based on the National Survey of Drug Use and Health (NSDUH). Past-month use of cannabis among 12 to 17 year-olds in Colorado was estimated at 6.7 per cent in 2005/2006 before rising to 12.6 per cent in 2013/2014, ranking Colorado’s youth as the leading consumers of cannabis in the U.S. Since this increase took place over a period of time during which recreational cannabis became legal (Colorado voted to legalize cannabis in 2012, with the first state-licensed retail outlets opening in 2014), Conservative MPs charged that legalization was the driver of escalating cannabis use among youth.

However, this implication overlooks the fact that much of the increase took place before legalization. There was only a 1.4-percentage point increase following legalization, which proceeded to drop again by 1.5 percentage points in 2014/2015. Dr. Larry Wolk, Director of the Colorado Department of Public Health and Environment, has also dismissed the claim that legalization led to increased use among young people.

Data from the Healthy Kids Colorado Survey, collected biannually by the Colorado Department of Public Health and Environment and the University of Colorado, further calls this claim’s validity into question. According to the 2015 survey, 21.2 per cent of Colorado high school students reported using cannabis in the previous month — a rate that has remained relatively unchanged from 22 per cent in 2011.

Even if rates in these reports were found to have increased significantly since legalization, any population health researcher would strongly caution against making statements about causality. This is because the changes in state rates were not tested against simultaneous changes in other state rates, and other potential state-level drivers of changing cannabis use patterns were not controlled for in statistical analyses.

Recent peer-reviewed research compared Colorado and Washington rates over a five-year period to 45 states without recreational cannabis and found that cannabis use has not increased significantly among high school students in Colorado since legalization. The study did note that in Washington, rates have increased slightly yet significantly among Grade 8 and 10 students since legalization, alongside noted decreases in perceived harmfulness of cannabis among them.

Claim #2: Cannabis impaired driving and traffic fatalities have increased in Colorado and Washington since legalization

Impaired driving is a top concern related to cannabis legalization. But before looking at how it could be affected by legalization, we should first note that the House debates revealed a great deal of misinformation about cannabis-impaired driving among our elected representatives.

Let’s first consider what is actually known about the effects of cannabis on driving:

Cannabis use produces dose-dependent acute impairments in motor skills, coordination and cognitive processes that can result in slower reaction time, poorer short-term memory and lower attention span. In simulated driving tests, subjects who are given cannabis tend to exhibit lower average speeds; increased following distances, lane weaving, and reaction times; and a reduced ability to divide attention between tasks while driving, compared to subjects who are given placebo cannabis. The most recent scientific review estimated a 22-36 per cent increased risk of a motor vehicle accident among drivers after using cannabis compared to drivers who did not use any substances. For comparison, drivers with a blood alcohol concentration (BAC) of 0.08 — the legal alcohol limit in many jurisdictions — are estimated to have a 169 per cent increased risk of a fatal accident. In fact, the increased risk of accidents associated with cannabis use is also less than the risks associated with widely used prescription pharmaceutical drugs like benzodiazapines(e.g. Valium, Ativan), and is more similar to the risk associated with the use of common over-the-counter medications such as antihistamines. However, as is the case with these other drugs, using cannabis together with alcohol can lead to a combined risk of a motor vehicle accident greater than the sum of their individual effects.

A recent study looked at changes in traffic fatality rates before and after medical cannabis legalization in U.S. states, using states without medical cannabis laws as controls, and found that legalization was associated with reduced rates of traffic deaths. A recent study looked at changes in traffic fatality rates before and after medical cannabis legalization in U.S. states, using states without medical cannabis laws as controls, and found that legalization was associated withrates of traffic deaths.

Although the risk of a motor vehicle accident is substantially lower than it is for the legal alcohol limit and widely used prescription and over-the-counter medications, cannabis is by no means harmless when it comes to driving. If legalization leads to more drivers deciding to drive high, statistically speaking we should expect to see a rise in the number of motor vehicle accidents. But is this what we are seeing in Colorado and Washington?

Last fall, alarming media reports warned of rising rates of fatal accidents among impaired drivers in Colorado and Washington. Although the headlines were gripping, upon closer inspection of the Colorado Department of Transportation and AAA Foundation for Traffic Safety reports from which they were drawn, the message was less clear.

First, what actually increased was the proportion of driver fatalities in which ≥1 ng/mL of tetrahydrocannabinol (THC — the main psychoactive component in cannabis) was detected in the blood. What this data does not tell us is how many of these drivers were actually impaired at the time of the accident. In Colorado and Washington, the legal limit for blood THC is 5 ng/mL, meaning an unknown portion of these drivers would not have been considered impaired under the current state laws.

More importantly, unlike alcohol, for which a BAC threshold is an accepted measure of impairment, there is no equivalent threshold for cannabis impairment. THC is fat-soluble and metabolized much differently than alcohol, such that traces of it can last in the bloodstream for hours or days after a period of impairment, depending on how often you use it. This means that any increase in THC detected among fatally injured drivers may simply indicate an increase in cannabis use among adults who drive. In Colorado, for example, since rates of cannabis use among adults did increase significantly after legalization, while the overall number of motor vehicle fatalities has been relatively stable, this alternative interpretation seems quite plausible.

As with youth cannabis use, inferring any kind of cause-and-effect relationship between legalization and traffic fatalities would be premature. There is no valid comparison group, and other relevant factors have not been taken into account, including co-occurring alcohol use and potential changes to testing practices for cannabis.

Interestingly, a recent study looked at changes in traffic fatality rates before and after medical cannabis legalization in U.S. states, using states without medical cannabis laws as controls, and found that legalization was associated with reduced rates of traffic deaths, leading the authors to hypothesize drivers were substituting cannabis for alcohol more often in legalized states. If drivers are indeed using cannabis instead of other drugs that more strongly impair driving, then legalizing cannabis use might actually result in safer roads.

In general this points to the importance of considering the effects of cannabis legalization on drug use more broadly, since looking at cannabis use on its own might give us a misleading picture of the true public health consequences.

Claim #3: Cannabis legalization led to increased organized crime activity and explosive illicit markets in Washington, Colorado and Uruguay.

Close behind preventing youth cannabis use, “keeping profits out of the hands of criminals” has been the Liberals’ mantra for justifying cannabis legalization. The opposition Conservatives, who previously spent millions of dollars in public funds enforcing prohibition, are reluctant to believe that loosening criminal penalties for cannabis use will hurt organized crime. In fact, several Conservative MPs even suggested that Canadians can expect to see a thriving illicit market and increased organized criminal activity, as has been (apparently) documented in Uruguay, Colorado and Washington.

The basis for this claim is not clear, particularly considering how dramatically the repeal of alcohol prohibition in the U.S. is widely known to have diminished the role of gangsters in the alcohol business. Tom Wainright, author of Narconomics: How to Start a Drug Cartel, writes that in Colorado and Washington, licensed sales of cannabis account for an estimated 70 per cent and 30 per cent of the total demand, respectively (lower cannabis taxes in Colorado are thought to play a big role in controlling the market). The remaining 30 per cent of demand in Colorado is thought to be met through illicit sales of legally homegrown product, while the remaining 70 per cent of demand in Washington is thought to be met through the untaxed, unlicensed so-called medical cannabis market. Although the illicit market has certainly not been eradicated in either state, evidence of a rising organized crime presence in these two states is lacking.

Perhaps this claim is based on the situation in Uruguay, which became the first country in the world to legalize cannabis in 2013. In 2016, Uruguayan authorities reported that cannabis seizures had increased almost three-fold since 2014, suggesting that there had been an increase in drug trafficking.

Assuming this data does in fact represent an increase in organized crime (drug seizures are notoriously unreliable metrics), using Uruguay’s regulatory model as a basis to predict Canadian outcomes seems inappropriate considering key differences between the Uruguayan and Canadian approaches. Uruguay’s system has been criticized for its strict regulatory approach, which requires consumers to sign up on a national registry and imposes limits on the monthly allowance of product per consumer. Furthermore, access to regulated cannabis has been hindered by low buy-in from pharmacies as the only authorized distributors.

Interpretation of this claim within the context of Uruguay’s legalization efforts reveals the potential role of over-regulation in contributing to the apparent increase in organized criminal activity related to cannabis — but this was not discussed in the House of Commons. Overall, given a lack of peer-reviewed research in this area, any interpretation of the information provided here should be done cautiously.

After a thorough review, we found very little evidence to support these three commonly cited claims about the health and social impacts of cannabis legalization. Given that such claims have a history of finding their way into our media reports, public discourse and policies, we should be careful to accept at face value any predictions made on their basis.

Doing so would mean ignoring science in support of political rhetoric that has been cleverly leveraged by curated bits of evidence to suit an ideological narrative. The 1950s propaganda associated with “Reefer Madness” might be a thing of the past — something we laugh off as unscientific fear-mongering — but the underlying ideals still appear to be quite alive in our House of Commons.

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