Have you ever wondered if there’s a natural way to lower your high blood pressure, guard against Alzheimer's, lose weight, and feel better? Well as it turns out there is. Michael Greger, M.D. FACLM, founder of NutritionFacts.org, and author of the instant New York Times bestseller “How Not to Die” celebrates evidence-based nutrition to add years to our life and life to our years.

The Health Effects of Marijuana

Today we look at new research on the health effects of marijuana.

This episode features audio from The Institute of Medicine Report on the Health Effects of Marijuana and Researching the Health Effects of Marijuana. Visit the video pages for all sources and doctor’s notes related to this podcast.


Health!  Wealth!  Happiness!  I’m Dr. Michael Greger and you’re listening to the Nutrition Facts podcast.  And while I can’t promise you all of those things, if you take a listen to the evidence-based nutrition found in this podcast, chances are you’ll learn something that you can use to make a positive change in your diet and in your health.  My job here is to bring you the information you need to make that reality possible.

Remember Mary Jane?  No – I don’t mean – the girl you went to grade school with.  I’m talking about a substance also known as cannabis.  Well, there’s a new research summary from the National Academies of Sciences.  What did this 468-page report conclude about cannabis and health?

When some misinformed people hear of the grand opening of a new plant-based medical practice, one plant in particular may come to mind. Over the years, I’ve gotten a lot of questions about cannabis, and I figure it’s high time to try to clear the haze. I didn’t want to just take a pot shot, tokin’ effort, and end up with some 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. I mean, are there acute chronic effects? Blunt trauma from impaired driving, perhaps? I wanted to give the straight dope; weed out any doobieous research, and it’s been quite a trip. 420 articles published within just the past few months!

Here’s the results of the review everyone was waiting for: “The [2017] Current State of Evidence” from the Institute of Medicine, “tasked with conducting a comprehensive review [on] the health effects of…cannabis.” Started out with 24,000 sources; whittled it down to about 10,000 to produce this 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 so too the purported risks. So, good news for the recreational user, who is mostly just worried about not getting cancer, but bad news for the patient who actually wants it to help their cancer. The only three benefits they could find “substantial evidence” for was as a treatment for “chronic pain in adults,” “chemo…-induced nausea and vomiting,” and relieving self-reported muscle tightness in patients with MS. 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. I mean, it does lower pressure, but only for “about an hour.” And so, you’d have to smoke a dozen joints a day—and even if you did smoke those few thousand a year, your body gets used to it. And so, what little benefit there is disappears within a few months in most patients.

On the other hand, conspicuously missing from this list of adverse side effects of long-term or heavy use is any mention of chronic obstructive pulmonary diseases, like emphysema, which you can get from smoking tobacco. And similarly, it doesn’t look like smoking marijuana increases the risk of respiratory cancers, like 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, appearing to increase risk about 50%—but only, it seems, for those smoking once a week or more, or for ten years or longer.

So, what did they conclude overall? Were they for legalization; opposed? Basically, they concluded, there simply isn’t enough research—”leaving patients, health care professionals, and policy makers without the evidence they need to make sound decisions” either way. Further: “This lack of evidence-based information…poses a public health risk.”

That’s one thing everyone on both sides can agree on: “the need for definitive clinical research.” Otherwise, we’re just left with “[a]necdotes,…blogs, and ad[s], which don’t “provide a sound basis for assessing the safety and efficacy of pharmacologic agents.” “Because cannabis is [just] a naturally occurring plant, and cannot be patented,” the pharmaceutical industry is MIA.

What we need are large clinical trials. Until then, we’re all just going to be “scratching our heads.” But, where’s the funding going to come from? For drug companies, interest in the plant is scant—where’s the payback?

Big Pharma is interested in “a reasoned approach,” however. “[T]he development of newer…cannabinoid modulators” in profitable pill form will, one day, writes this pharmacology professor, “make…the use of herbal cannabis a thing of the past.”

As you might expect – politics, prejudice, and pressure coming from both sides adds to the complexity of cannabis research.

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?…Why did the pharmaceutical industry fail to show any interest? Some might prefer a simple answer; since [it’s] just [a plant], it can[’t] be patented [for your stockholders], thus removing any incentive for investing…corporate funds.” Yes, but it’s more complicated than just that.

There are research funds available—a hundred million dollars of public money in a single year—but, historically, that money was generally “obtainable only for research on the negative effects.” See, in the U.S., cannabis is still officially lumped in with heroin as “a Schedule I drug”—which means, by definition, it’s classified by the government to have no medicinal value, a designation that “resulted in a near-cessation of scientific research, particularly” since the only way researchers could get it without risking jail time is a state-run farm in Mississippi, controlled by the National Institute on Drug Abuse, which has historically only greenlighted research aimed at “demonstrating…harmful effects.”

“Residents of 23…states can” walk out and just buy it, “but US scientists must wade through onerous paperwork,” and even when they do get it, it’s the wrong stuff; it’s not what people are actually using these days. The studies coming out are on like your grandma’s grass, a few percent THC, where the stuff available these days may be ten times more potent.

So, there’s like this 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.” So, “[i]ll-informed practitioners are thus left to make do with” like, anecdotes off the internet, like everybody else, which 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. That’s no excuse, though. Just because there are “[p]olitical 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, now there’s pressure coming from both sides. The marijuana industry is now big business, and with those billions, can rally the troops. “Cannabis researchers already talk of being bombarded with e­mails from pro­-cannabis groups if they [dare] 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.

But the barriers go beyond money, politics, and prejudice. Cannabis research is hard to do. I mean, how do you do a double-blind study with marijuana? People know when they’ve been duped with placebo dope. People can tell the difference between pot brownies and regular brownies; otherwise, they wouldn’t eat them. And so, if you know you’re getting the active drug, the placebo effect can kick in hard, notes one neurobiology researcher, 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’re asking heavy pot smokers to try to remember how much they’ve been smoking over their life. I mean, you can imagine 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 it’s not a matter of motivation, rather than actual cognitive impairment? That had never been tested, until now. They gave a group of potheads a standard learning test and just gave the standard spiel, you know: “Please complete the following series of tasks which measure different areas of cognition, like memory and attention.” That’s what you’d normally say, and when you do, pot smokers score significantly worse. Ah, but what if you instead said this: “Please complete the following series of tasks… 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, hey, if you do good, they might decriminalize weed or something. And, under those circumstances, boom: the apparent cognitive impairment disappears.

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

To see any graphs, charts, graphics, images or studies mentioned here, please go to the Nutrition Facts podcast landing page.  There, you’ll find all the detailed information you need – plus links to all the sources we cite for each of these topics.

Be sure to check out my new How Not to Die Cookbook.  It’s beautifully designed, with more than 100 recipes for delicious, health-promoting meals, snacks, beverages, desserts.  Not just every recipe is healthy—every ingredient of every recipe is healthy, all green-light whole plant foods.  And, of course, all the proceeds I receive from the sales of my books all go to charity. 

NutritionFacts.org is a nonprofit, science-based public service, where you can sign up for free daily updates on the latest in nutrition research via bite-sized videos and articles.

Everything on the website is free. There are no ads, no corporate sponsorship.  It’s strictly non-commercial.  I’m not selling anything. I just put it up as a public service, as a labor of love—as a tribute to my grandmother – whose own life was saved with evidence-based nutrition.

Thanks for listening to Nutrition Facts. I’m Dr. Michael Greger.

This is just an approximation of the audio content, contributed by Allyson Burnett.


5 responses to “The Health Effects of Marijuana

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  1. Thank you for addressing the current issue in cannabis research. Can you please cite the papers so that I can get an unbiased opinion?

    Thank you for your help in making lives healthier!

  2. Hello,
    thank you for addressing the current issue with cannabis research, which is holding back the whole world, and similar to plant based diets, is held back by a big industry with only money in mind. Can you please cite your sources so I can get an unbiased opinion?

    Thank you for your service in making our lives healthier.

  3. What about 0 THC cbd oil? It seems it would be easy enough to conduct double-blind studies, since there is no associated “high.” I understand that oil is not the best source of food, but am curious about this particular oil’s potential benefits as medicine.

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