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The Medical Minute: Wait, Did They Really Just Equate Cannabis to Heroin?

In this week’s “I Can’t Believe It’s Not Satire,” Medical Minute, the media compares cannabis’ addictive potential to heroin following the release of a 20-year study aimed at the detriments of long-term cannabis use. Other risks these news stories capitalize on include an increased likelihood of psychosis, cognitive and intellectual decline, birth complications, driving impairment, and the gateway drug theory. A flurry of these sensational headlines took the internet by storm last week, our favorites being “Cannabis as addictive as heroin, major new study finds,” “20-year study finally demolishes claims that smoking pot is harmless,” and, of course, “Shocker: 20-year study says that marijuana makes you stupid.”

You have to wonder if these authors were simply shooting for click-bait, because when reading the study’s text, you’ll see quite a few interpretive wrinkles that need ironing out.

Aiming for the Adverse

Before diving into media-fueled misinterpretations, it’s important to first understand what this study is and what it aimed to accomplish. The word “study” in this instance is a bit of a misnomer; more accurately, this is a meta-analysis – a review – of studies performed since 1993. Just read the publication’s “aim”: to examine changes in the evidence on the adverse health effects of cannabis since 1993. No new research was performed; rather, evidence of impairment, dependence, and complications were pulled together to create a partial picture.

Take a look at the review’s 165 citations: either they offer support to the claim that marijuana causes harm, or they conclude that there is insubstantial evidence to draw a causal relationship between cannabis use and the detriments in question. So yes, this study takes into account a wide body of research – but what’s excluded is just as important.

At What Point is Cannabis Harmful?

One distinction many news outlets failed to catch is this study’s focus on heavy, long-term cannabis use – meaning daily or near-daily consumption. These findings are reported out of context, simply saying that cannabis has been shown to cause x, or cannabis use is associated with y. Where does the infrequent or moderate user fall in the risk matrix? You won’t find the answer in this 20-year survey or the news sources summarizing it.

The Problem with Absolutes

Cannabis use doesn’t occur in a vacuum. It’s consumed in conjunction with a personality, a lifestyle, experience, and an unlimited number of nuanced circumstances that creep into the scientific method whether we want them to or not. Let’s take the gateway drug theory for example, since the study’s authors address this conflation head-on.

“A major challenge in interpreting associations between regular cannabis use and adverse health outcomes in epidemiological studies is that regular cannabis users differ from non-users in a variety of ways that may reflect baseline differences in their risks of adverse outcomes,” the authors write. “Regular cannabis users, for example, are more likely to use alcohol, tobacco and other illicit drugs, and they differ from non-users in their risk-taking and other behavior.”

A less obvious example is cannabis and pregnancy; this review mentions that throughout adolescence, cannabis-exposed children typically perform worse in school with diminished cognitive abilities. Researchers acknowledge several caveats that media sources seemed to glaze over: things like socioeconomic status, parenting style, other drug use – could these factors play a part? Hint: yeah, they absolutely do.

What Can We Learn From This, Then?

At no point does this study claim that cannabis is as addictive as heroin or that it will make you stupid. Even with an arsenal of studies analyzing the harm of cannabis use, the researchers acknowledge that there is much uncertainty to unravel. All of this is not to say that heavy, long-term cannabis use doesn’t come with complications; every pleasurable thing in this world has the potential to be abused, even our most beloved flower. Cannabis advocacy suffers when we ignore its negative realities and blindly propagate what we want to believe is true. But the heart of the issue is this: think critically and intelligently about everything you read, whether it’s written in the name of science, news, or opinion. Could there be a better way to demonstrate the irony of the statement cannabis causes intellectual decline?

(Also, a hat tip to Washington Post for their thorough clarification of this study's findings.)