Scientists Speak Against False Cannabis Claims

The International Centre for Science in Drug Policy (ICSDP) is a network of scientists and academics 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. By conducting research and public education on best practices in drug policy while working collaboratively with communities, policy makers, law enforcement and other stakeholders, the ICSDP seeks to help guide effective and evidence-based policy responses to the many problems posed by illicit drugs.

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 ground-breaking reports 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 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 legalising 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 scaremongering and came clean with the public about the facts when it comes to regulating cannabis.” The new reports are a resource for journalists, policy-makers, and members of the general public who would like to engage with the complex issues surrounding global cannabis use and regulation.

COMMON CLAIMS ON CANNABIS USE

Claim - “Cannabis is as addictive as heroin”
Strength of Supporting Evidence - Weak
Bottom Line - A lifetime of cannabis use carries a low risk of dependence (9%), while the risk of cannabis dependence is very low among those who report using it for one year (2%) or even 10 years (5.9%). This is much lower than the estimated lifetime risk of dependence to heroin (23.1%).

Claim - “Did you know that cannabis is on average 300 to 400% stronger than it was thirty years ago?”

Strength of Supporting Evidence - Moderate

Bottom Line - Although this claim overstates the existing evidence, studies do suggest that there have been increases in Tetrahydrocannabinol (THC) potency over time in some jurisdictions.

Claim - “I’m opposed to legalising cannabis because it acts as a gateway drug.”
Strength of Supporting Evidence - Weak

Bottom Line - Evidence to date does not support the claim that cannabis use causes subsequent use of 'harder' drugs.

Claim - Cannabis use “can cause potentially lethal damage to the heart and arteries.”
Strength of Supporting Evidence - Weak
Bottom Line - There is little evidence to suggest that cannabis use can cause lethal damage to the heart, nor is there clear evidence of an association between cannabis use and cancer.


Claim - Cannabis use lowers IQ by up to 8 points.

Strength of Supporting Evidence - Weak

Bottom Line - There is little scientific evidence suggesting that cannabis use is associated with declines in IQ.

Claim - Cannabis use impairs cognitive function.

Strength of Supporting Evidence - Moderate

Bottom Line - While the evidence suggests that cannabis use (particularly among youth) likely impacts cognitive function, the evidence to date remains inconsistent regarding the severity, persistence and reversibility of these cognitive effects.

Claim - “Cannabis is a drug that can result in serious, long-term consequences, like schizophrenia.”
Strength of Supporting Evidence - Weak
Bottom Line - While scientific evidence supports an association between cannabis use and schizophrenia, a causal relationship has not been established.

COMMON CLAIMS ON CANNABIS REGULATION 

Claim - Legalisation / regulation increases the availability of cannabis.
Strength of Supporting Evidence - Weak
Bottom Line - Evidence suggests that the supply of illegal cannabis has increased under a prohibition model and that availability has remained high among youth. Evidence does not suggest that cannabis availability among youth has increased under regulatory systems.


Claim - “If cannabis was legalised, the increase in users would be both large and rapid …”
Strength of Supporting Evidence - Weak
Bottom Line - Evidence suggests that the policy environment (specifically legal status and enforcement policy) has at most a marginal impact on the prevalence of drug use, thereby suggesting that regulating cannabis markets will not inevitably cause higher levels of cannabis use.

Claim - Regulation will not reduce drug crime. 
Strength of Supporting Evidence - Weak
Bottom Line - Given that the prohibition of cannabis has not been shown to reduce illegal supply, it is likely that cannabis regulation is more effective at minimising criminal markets for cannabis, despite the fact that criminal markets will continue to represent a proportion of the total market.

Claim - “We are going to have a lot more people stoned on the highway and there will be consequences.” 

Strength of Supporting Evidence - Weak
Bottom Line - While experimental studies suggest that cannabis intoxication reduces motor skills and likely increases the risk of motor vehicle collisions, there is not sufficient data to suggest that cannabis regulation would increase impaired driving, and thereby traffic fatalities.

Claim - Regulation promotes drug tourism. 
Strength of Supporting Evidence - Weak
Bottom Line - There is a great deal of uncertainty regarding cannabis regulation and so-called “drug tourism” and it is likely that such activity will vary across different jurisdictions based on the use of different regulatory controls.

Claim - Regulation leads to a “Big Cannabis” scenario.

Strength of Supporting Evidence - Weak
Bottom Line - Available evidence regarding “Big Cannabis” is currently lacking, though regulatory controls can be introduced within regulatory systems to reduce the potential of profit maximisation by cannabis retailers

Resources;

Cannabis Global
State of the Evidence Cannabis Use and Regulation