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What Is the Science on Cannabis?

What did the National Academies of Sciences’ 468-page report conclude about cannabis? 

When some misinformed people hear of the grand opening of a new plant-based medical practice, one plant in particular may come to mind. I’ve gotten a lot of questions about cannabis over the years, and I figure it’s high time to try to clear the haze. I didn’t want to just take a pot shot, just a tokin’ effort, and end up with a half-baked puff piece. There are burning issues about a growing industry. With so much buzz and smoke and mirrors, the science can really take a hit. Are there acute chronic effects? Perhaps blunt trauma from impaired driving? I wanted to give the straight dope and weed out any doobie-ous research. It’s been quite a trip. In fact, 420 articles were published within just a few months! 

My video The Institute of Medicine Report on the Health Effects of Marijuana dives into the review everyone was waiting for: the 2017 “current state of evidence” from the Institute of Medicine “tasked with conducting a comprehensive review of…the health effects of using cannabis and cannabis-derived products.” The reviewers started with 24,000 sources, which they whittled down to about 10,000 from which they produced a 468-page document. What did they find? 

I think it’s fair to summarize that they found the purported benefits to be much smaller and weaker than are often reported, but they found the same for the purported risks. So, that’s good news for the recreational user who is mostly just worried about not getting cancer, but it’s bad news for the patient who actually wants it to help their cancer. They did find substantial evidence for some benefits, but only three—in the treatment of chronic pain in adults, the treatment of chemotherapy-induced nausea and vomiting, and for relieving self-reported muscle tightness in patients with multiple sclerosis. Even archetypal medical marijuana indications, like glaucoma, failed to live up to expectations. 

Despite popular belief to the contrary, extensive research over decades has documented that marijuana is not effective in the management of clinical glaucoma, a disease of increased pressure within the eyeball. Marijuana does lower pressure, but only for about an hour, so you’d have to smoke a dozen or so joints a dayEven if you did smoke those few thousand joints a year, though, your body gets used to it, so what little benefit there is disappears within a few months in most patients. 

On the other hand, conspicuously missing from the list of adverse side effects of long-term or heavy marijuana use, which you can see at 2:42 in my videois any mention of chronic, obstructive, pulmonary diseases like emphysema, which you can get from smoking tobacco. Similarly, it doesn’t look like smoking marijuana increases the risk of respiratory cancers, such as lung cancer or head and neck cancer, though cannabis may increase the risk of testicular cancer. There have been three studies so far on marijuana use and testicular cancer. As you can see at 3:10 in my video, marijuana appears to increase risk about 50 percent, but only, it seems, for those smoking once a week or more, or for ten years or longer. 

What did the Institute of Medicine conclude overall in its 468-page report? Were they for legalization, or opposed? Basically, they concluded that there simply isn’t enough research, leaving patients, health care professionals, and policy makers without the evidence they need to make sound decisions regarding the use of cannabis and cannabinoids either way. Further, this lack of evidence-based informationposes a public health risk. 

The one thing everyone on both sides “can agree [on] is the need for definitive clinical research on marijuana.” Otherwise, we’re just left with “anecdotes, Internet blogs, and advertisements [that] do not provide a sound basis for assessing the safety and efficacy of pharmacologic agents.”  

Because cannabis is a naturally occurring plant and cannot be patented, the pharmaceutical industry is MIA. What we need are large clinical trials. Until then, we’re still going to be left scratching our heads,” but where will the funding come from? For drug companies, interest in the plant is scant” because where’s the payback? 

Big Pharma is interested in a reasoned approach, however. Writes pharmacology professor Harold Kalantone day, the development of newer…endocannabinoid modulators”—in profitable pill form, that is—“will make the use of herbal cannabis a thing of the past. 

Why is there such a “dearth of rigorous research on the effects of marijuana”? The first major study wasn’t published until 2007. “Why did it take so long for this study to appear in the peer-reviewed scientific literature? Why did the pharmaceutical industry fail to show any interest in this promising compound? Some might prefer a simple answer: since marijuana is a naturally-occurring botanical”—since it’s just a plant—”it cannot be patented, thus removing any incentive for investing…corporate funds…” Yes, but it’s more complicated, as I discuss in my video Researching the Health Effects of Marijuana. 

In fact, research funds are available—“$111 million…in 2015 alone,” for example—but, historically, “that money generally has been obtainable only for research on the negative effects of cannabis.” In the United States, cannabis is still officially lumped in with heroin as a Schedule I drug, which means that, by definition, it is classified by the government as having no medicinal value. “This designation has resulted in a near-cessation of scientific research,” particularly because the only way researchers could get cannabis without risking jail time is from the only federally authorized source, a strain grown in Mississippi and controlled by the National Institute on Drug Abuse. What’s more, historically, the NIDA has only greenlit research aimed at demonstrating “harmful effects.” 

“Residents of 23 US states can buy medical marijuana…but US scientists must wade through onerous paperwork to score the drug for study.” And, even when they do get it, it may be the wrong stuff. The cannabis from that one federally authorized farm in Mississippi “‘may differ substantially’ from what people purchase for real-world consumption”—that is, it may not be what people are actually using these days. As a result, the studies coming out may be on your grandma’s grass, for instance, “with potency levels between 3.5 and 7.0% THC,” whereas the marijuana available these days may be ten times more potent.  

So, there is a crazy “catch-22,” where “the cannabis that should be studied…is illegal and the cannabis that can be legally studied—the decades-old Mississippi strain—is essentially kept off-limits.” Because of this, “ill-informed practitioners are thus left to make do with anecdotal testimony and case reports—the least rigorous form of evidence—to guide their prescribing.” Basing treatment off stories from the internet is bad medicine. 

“As long as clinical research on Cannabis is controlled by regulators expressly opposed” to the stuff, we may miss out on potential benefits—but that’s no excuse. Just because there are political barriers to research doesn’t mean we should lower our bar in terms of demanding evidence. “The sick still need medically sound treatments.” 

Of course, there’s now pressure coming from both sides. The marijuana industry has become big business and, with its billions, can rally the troops. “Cannabis researchers already talk of being bombarded with e­mails from pro­cannabis groups if they make any negative comments about the drug. ‘Marijuana research is like tobacco research in the ’60s,’” says one University of Colorado researcher. So now, there’s fear Big Money will push the pendulum too far the other way.  

The barriers go beyond money, politics, and prejudice, though. Cannabis research is hard to do. How do you do a double-blind study with marijuana? People know when they’ve been duped with placebo dope, and they can tell the difference between pot brownies and regular brownies. So, if you know you’re getting the active drug, the placebo effect can kick in hard, especially when you’re dealing with subjective outcomes like pain or mood. 

And imagine if you’re trying to do a population study on memory or cognitive impairment, and you have to ask heavy pot smokers to try to remember how much they’ve smoked over their life. You can guess how that might “influence data accuracy.” 

Let me give you an example of how convoluted this can get. Neuropsychological testing of cannabis users have found residual negative effects in terms of scoring slightly lower on memory tests, but how do we know that wasn’t just a matter of motivation (or lack thereof), rather than actual cognitive impairment? That had never been tested until researchers gave a group of potheads a standard learning test with the instruction: “Please complete the following series of tasks which measure different areas of cognition, like memory and attention.” With that standard spiel, pot smokers scored significantly worse than non-users, as you can see at 4:35 in my video. Okay, but what if the study participants heard the standard spiel and were also told: “It is important that you try your very best on these tasks, because this research will be used to support legislation on marijuana policy.” So, one might infer that if you do good, weed might get decriminalized or something! And, under those circumstances, BOOM—the apparent cognitive impairment disappears, as you can see at 4:57 in my video 

Now, you could argue that lack of motivation is a problem in and of itself, but it’s better than having long-term brain damage. 

KEY TAKEAWAYS

  • Tasked with conducting a comprehensive review of the health effects of cannabis, the Institute of Medicine released a 468-page report.
  • In sum, the researchers found less benefit but also less risk than is often claimed.
  • Substantial evidence was found for the treatments of chronic pain in adults and chemotherapy-induced nausea and vomiting, as well as relieving self-reported muscle tightness in individuals with multiple sclerosis, but not for the management of glaucoma, despite popular belief otherwise.
  • Unlike smoking tobacco, long-term or heavy marijuana-smoking habits do not appear to have the same adverse side effects of chronic, obstructive pulmonary diseases like emphysema, and smoking cannabis does not seem to increase risk of respiratory cancers, though it may elevate testicular cancer risk.
  • Overall, the Institute of Medicine determined there is a lack of evidence-based information, which poses a risk to public health.
  • One reason cannabis is under-studied is that it is a naturally occurring plant that cannot be patented, so drug companies are disinclined to invest in research about its effects. What’s more, most research that has been conducted has focused on its negative impacts.

If you’d like to learn more about the effects of marijuana on healthcheck out: 


In health, 

Michael Greger, M.D. 

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations: 

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Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.


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