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. 

“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.”

The review also found that many claims about cannabis regulation overlook an important fact: that regulation shifts control of cannabis markets from criminal entrepreneurs and into the hands of government. According to Dr. Werb, “Claims that regulation leads to large, for-profit cannabis industries with little oversight and a lack of concern about public health and safety, referred to as a ‘Big Marijuana’ scenario, underestimate the range of regulatory controls available to policymakers to minimize undesired outcomes. The use of not-for-profit cannabis social clubs in Spain is one such control. Bans on advertising, as has been implemented in Uruguay, is another example.”

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. Scientists and academics will be holding an ongoing conversation on Twitter using the hashtag #CannabisClaims at the @icdsp handle starting on August 12, 2015. Interested parties can also sign up for the ICSDP newsletter to get updates on how supporters around the world are coming together to bring scientific evidence to the public discourse on cannabis.

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. Momentum towards regulation continued in the United States in 2014 with successful ballot initiatives in Alaska, Oregon, and the District of Columbia. A number of additional U.S. states, including California, are set to vote on legalization initiatives in 2016. As the conversation progresses in the U.S., these reports are intended to provide an evidence base for decisions on cannabis policy.

About the International Centre for Science in Drug Policy
The International Centre for Science in Drug Policy (ICSDP) is a network of scientists and academics from all global hemispheres committed to improving the health and safety of communities and individuals affected by illicit drugs by working to inform illicit drug policies with the best available scientific evidence. With the oversight of a Scientific Board made up of leading experts on addictions, HIV, and drug policy, the ICSDP conducts research and public education on best practices in drug policy. This work is undertaken in collaboration with communities, policymakers, law enforcement and other stakeholders to help guide effective and evidence-based policy responses to the many problems posed by illicit drugs.

For more information or to arrange a media interview, please contact:
Nazlee Maghsoudi
Knowledge Translation Manager, ICSDP
+1 (647) 694-9199
nmaghsoudi [at] 


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