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State of the Evidence : Cannabis Use and Regulation

Scientists speak out against false cannabis claims

Leading international scientific body reviews thirteen oft-repeated claims on cannabis use and regulation, finds that none are strongly supported by scientific evidence

Toronto, Canada – Many scientists are increasingly frustrated by the disregard of scientific evidence on cannabis use and regulation. To set the record straight, the International Centre for Science in Drug Policy (ICSDP), a global network of scientists working on drug policy issues, released two groundbreaking reports today evaluating the strength of commonly heard cannabis claims.

“State of the Evidence: Cannabis Use and Regulation, » is a comprehensive overview of the scientific research on major claims made about cannabis. It is paired with a summary report, « Using Evidence to Talk About Cannabis, » which equips readers with evidence-based responses to the claims. 

The regulation of recreational cannabis markets has become an increasingly important policy issue in a number of jurisdictions. Colorado and Washington State made headlines in 2012, and Uruguay in 2013, when they became the first jurisdictions in the world to legalize and regulate the adult use and sale of cannabis for non-medical purposes. Momentum towards regulation continued in the United States in 2014 with successful ballot initiatives in Alaska, Oregon, and the District of Columbia. Globally, the issue of cannabis regulation is front and center in a growing number of jurisdictions, including Canada, Jamaica, Italy, Spain, Latin America, as well as several U.S. states set to vote on legalization initiatives in 2016.

“We are at a critical juncture, as more and more jurisdictions are reconsidering their policies on cannabis,” said Dr. Dan Werb, Director of the ICSDP. “Yet, the public discourse around cannabis is filled with frequently repeated claims that are simply not supported by the scientific evidence. Given that policy decisions are influenced by public opinion and media reports, there is a serious danger that misrepresenting the evidence on cannabis will lead to ineffective or harmful policy.”

To investigate this issue, the ICSDP convened scientists to conduct a review of thirteen oft-repeated claims about cannabis use and regulation. The review found that none of the claims were strongly supported by the scientific evidence.

The majority of cannabis use claims outlined in the reports tend to either misinterpret or overstate the existing scientific evidence. Dr. Carl Hart, Professor in the Departments of Psychology and Psychiatry at Columbia University, explained, “The claim that cannabis is a ‘gateway’ drug, for example, confuses correlation and causation. Worse still is the fact that a false claim like ‘cannabis is as addictive as heroin’ is reported as front page news. The evidence tells us that less than 1 in 10 people who use cannabis across their lifetime become dependent, whereas the lifetime probability of becoming heroin-dependent is closer to 1 in 4. False claims like these hamper public understanding of these issues and ultimately lead to harmful policies.”

“This in-depth global research refutes the false claim that legalizing and regulating cannabis would automatically lead to huge increases in use, to levels like those seen for tobacco and alcohol,” noted Mr. Steve Rolles, Senior Policy Analyst at the UK-based Transform Drug Policy Foundation. “With a growing body of evidence from more and more places reforming their drug laws, it is time our leaders stopped scare-mongering and came clean with the public about the facts when it comes to regulating cannabis.”

The new reports are a resource for journalists, policymakers, and members of the general public who would like to engage with the complex issues surrounding global cannabis use and regulation.

INTRODUCTION

Since inception, the International Centre for Science in Drug Policy (ICSDP) has sought to ensure that policy responses to the many problems posed by illicit drugs are informed by the best available scientific evidence.

S tate of the Evidence: Cannabis Use and R egulation

is the ICSDP’s contribution to the growing global conversation on cannabis. This report should be read in tandem with Using Evidence to Talk About Cannabis, a complementary guide to having evidence-based discussions on cannabis use and regulation.

The regulation of recreational cannabis mar- kets has become an increasingly important policy issue in a number of jurisdictions. Colorado and Washington State made headlines in 2012 when they became the first jurisdictions in the world to legalize and regulate the adult use and sale of cannabis for non-medical purposes. In 2013, Uruguay became the first country to legalize and regulate recreational cannabis markets. Momentum towards regulation continued in the United States in 2014 with successful ballot initiatives in Alaska, Oregon, and the District of Columbia. Globally, the issue of cannabis regulation is front and center in a growing number of jurisdictions, including Canada, Jamaica, Italy, Spain, several Latin American countries, and a number of additional U.S. states, including California, set to vote on legalization initiatives in 2016.

Unsurprisingly, given the robust global conver- sation around the regulation of recreational cannabis markets, claims about the impacts of cannabis use and regulation are increasingly part of the public discourse. Unfortunately, though, these claims are often unsupported by the available scientific evidence. Another reoccurring problem in the public discourse

is the selective inclusion of research studies based on their support for a predetermined narrative. The intentional exclusion of studies with contradictory findings does not allow for an objective review and analysis of all the evi- dence. This “cherry picking” of the evidence is a routine practice that distorts public under- standing. By outlining the current state of all the scientific evidence on common cannabis claims, State of the Evidence: Cannabis Use and Regulation strives to ensure that evidence, rather than rhetoric, plays a central role in policy-making around this important issue.

The harms of misrepresenting the scientific evidence on cannabis should not be over-looked. Given that policy decisions are influenced by public opinion and media reports, public discourse needs to be well informed. By addressing knowledge gaps with scientific findings, the ICSDP hopes to dispel myths about cannabis use and regulation, and ensure that the scientific evidence on these topics is accurately represented. Only then can evi- dence-based policy decisions be made.

Readers of this report will notice three repeat- ing themes emerge through the discussion of the scientific evidence on common cannabis claims.

First, many of the claims confuse correlation and causation. Although scientific evidence may find associations between two events, this does not indicate that one necessarily caused the other. Put simply, correlation does not equal causation. This is a commonly made mistake when interpreting scientific evidence in all fields, and is unsurprisingly a recurring source of confusion in the discourse on cannabis use and regulation.

Second, for several of these claims, the in- ability to control for a range of variables (“confounders”) means that in many cases, we cannot conclude that a particular outcome was caused by cannabis use or regulation. Unless scientists can remove all other possible expla- nations, the evidence cannot conclusively say that one specific explanation is true.

Third, many of the claims cannot be made conclusively as there is insufficient evidence to support them. Findings from a single study or a small sample cannot be generalized to entire populations. This is especially pronounced for claims related to cannabis regulation, as not enough time has passed since the regulation of recreational cannabis in Colorado, Washington State, and Uruguay to examine many of the impacts of these policy changes.

These three common pitfalls are important to take into account when reading media reports and advocacy materials that suggest scientists have conclusively made some finding related to cannabis use or regulation. In many cases, due to the reasons outlined above, this will actually result in a misrepresentation of the scientific evidence.

State of the Evidence : Cannabis Use and Regulation is comprised of two sections : Common Claims on Cannabis Use and Common Claims on Cannabis Regulation.

Common Claims on Cannabis Use presents evidence on frequently heard claims about can- nabis use, including claims on the addictive potential of cannabis, cannabis as a “gateway” drug, the potency of cannabis, and the impact of cannabis use on the lungs, heart, and brain (in terms of IQ, cognitive functioning, and risk of schizophrenia).

Common Claims on Cannabis Regulation presents evidence on frequently heard claims about the impacts of cannabis regulation, including the impact of regulation on cannabis availability, impaired driving, the use of cannabis, drug crime, drug tourism, and “Big Marijuana.”

For each claim, the relevant available scientific evidence is presented and the strength of the scientific evidence in support of the claim is determined. Readers will notice that none of the claims are strongly supported by the scientific evidence, reinforcing the significant misrepresentation of evidence on cannabis use and regulation.

We hope that the evidence contained in this report meaningfully contributes to the global conversation around cannabis policy and helps policymakers, as well as general readers, sepa- rate scientific evidence from conjecture.

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