Many of the common claims about marijuana -- that it's a gateway drug, for example, or that legalization of the plant often results in more people using it -- are not strongly supported by science, a group of researchers say in a report released Wednesday.
"Many scientists are increasingly frustrated by the disregard of scientific evidence on cannabis use and regulation," the International Centre for Science in Drug Policy said in a statement accompanying the release of its report, "State of the Evidence: Cannabis Use and Regulation."
The report is a comprehensive look at the science that does -- or doesn't -- support the conventional wisdom about marijuana use and policy. An accompanying summary document, "Using Evidence to Talk About Cannabis," provides an overview of the longer report.
The researchers listed 13 common claims about cannabis use and regulation -- most of them involving harmful consequences supposedly associated with the drug -- and tried to assess how well the current scientific literature supports those claims. They found that the majority of these assertions "tend to either misinterpret or overstate the existing scientific evidence."
Dr. Carl Hart, a professor in psychology and psychiatry at Columbia University who sits on the scientific board of ICSDP, outlined some examples in a statement.
“The claim that cannabis is a ‘gateway’ drug, for example, confuses correlation and causation," Hart said. "Worse still is the fact that a false claim like ‘cannabis is as addictive as heroin’ is reported as front page news."
The scientific evidence clearly illustrates that "less than 1 in 10" lifelong marijuana users become dependent on the drug, Hart said, whereas heroin dependency occurs in about 1 in 4 people.
"False claims like these hamper public understanding of these issues and ultimately lead to harmful policies,” Hart said.
The report's authors identified seven common arguments against marijuana use and found that the evidence in support of five of them was "weak."
For the other two claims, the researchers wrote, there is "moderate" evidence backing them up. One of those claims states that "marijuana is on average 300 to 400 percent stronger than it was thirty years ago."
"Although this claim overstates the existing evidence," the researchers write, "studies do suggest that there have been increases in THC potency over time in some jurisdictions."
They also found "moderate" scientific evidence for the claim that marijuana use impairs cognitive function, especially in young people. However, they wrote, "the evidence to date remains inconsistent regarding the severity, persistence, and reversibility" of those effects.
On Marijuana Use:
The group also identified six of the most frequently used arguments against the legal regulation of marijuana -- including that legalization could lead to more widespread use of the substance and that legalization does not reduce drug crime -- and in every case found the scientific evidence to be "weak."
“We are at a critical juncture, as more and more jurisdictions are reconsidering their policies on cannabis,” Dr. Dan Werb, ICSDP director and co-author of the report, said in a statement. “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 date in the United States, 23 states, along with the District of Columbia, have legalized marijuana for medical purposes. Four states and D.C. have legalized recreational marijuana for adults, although D.C. still bans sales of the drug. Several more states are expected to consider recreational legalization in the coming years.
Still, marijuana remains illegal under federal law, which classifies it as one of the "most dangerous" drugs -- in the same category as heroin and LSD -- and maintains that it has "no currently accepted medical use."
On Marijuana Regulation:
Some of the claims that the group analyzed are from Kevin Sabet, a vocal opponent of marijuana legalization who heads up the anti-legalization group Smart Approaches to Marijuana. Sabet blasted the report's findings in an email exchange with The Huffington Post.
"This reads like Big Tobacco propaganda of the 1950s," he wrote. "It's not surprising that a small group of well known legalization advocates and funders continue to deny the threat of Big Marijuana and advertising and promotion related to addiction."
At one point in the ICSDP report, Sabet is quoted personally as saying that cannabis "is a drug that can result [in] serious, long-term consequences, like schizophrenia" -- a claim that the report rates as "weak."
"I am citing all of the modern literature saying that cannabis can result in schizophrenia, not [that it] will cause schizophrenia," Sabet told HuffPost.
Advocates for marijuana policy reform praised the report.
Amanda Reiman, manager of marijuana law and policy for the Drug Policy Alliance, told HuffPost that although "cannabis was a widely recognized medicine for thousands of years, fear, racism, and the resulting propaganda have forced it into the category of 'dangerous drug' for the last several decades."
Still, she said, public perception of the substance is changing rapidly.
"The science is overtaking the propaganda," Reiman said. "This new series of investigations, from the top drug researchers in the world, moves us one step closer to reefer sanity."
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