Effects of Smoking Marijuana on the Lungs

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

“There is unequivocal evidence that habitual or regular marijuana smoking is not harmless and causes respiratory symptoms and airway inflammation.” If you take biopsies from the airways of those that smoke crack, cannabis, or tobacco, compared to nonsmokers, there is significantly more damage in the lungs of crack smokers, marijuana smokers, and tobacco smokers. And, the levels of damage seemed comparable—especially between the marijuana smokers and tobacco smokers—which is remarkable, since the tobacco smokers were smoking about a pack a day, whereas the marijuana smokers were only smoking about 20 joints a week, rather than 25 cigarettes a day. And those smoking crack were just doing a gram or two a week. So, to see similar rates of damage between marijuana smokers and cigarette smokers suggests each joint is way worse than each cigarette.

Indeed, we’ve known for 30 years that smoking three or four joints is the equivalent of smoking a pack a day of cigarettes, in terms of bronchitis symptoms and acute lung damage. How is that possible? Well, it may be the way they’re smoked. Pot smokers inhale more deeply, and then hold the smoke in four times longer, resulting in more tar deposition in the lungs. And, joints are more “loosely packed [and] unfiltered,” resulting in both “hotter smoke” and smokier smoke. So, even though in many ways smoke is smoke, the different “method of smoking” may explain how a few joints a day appear to cause as much inflammation as an entire pack a day of cigarettes.

“The visual evidence of airway injury was at times striking.” This is what your airways are supposed to look like—the tubes inside your lungs. This is your lung. This is your lung on tobacco; see how your airways get all inflamed? And, this is your lung on pot. You get the same kind of inflammation, and what’s crazy is that’s just five joints a day, compared to 26 cigarettes a day in the tobacco smokers.

If you compare the respiratory symptoms associated with marijuana versus tobacco, compared to nonsmokers, both marijuana smokers and tobacco smokers have elevated rates of chronic cough and excess sputum production, and acute episodes of bronchitis and wheezing. Now, when you quit tobacco, these respiratory symptoms eventually go away. Does the same thing happen with marijuana? What are the “effects of quitting cannabis on respiratory symptoms”?

About 30 to 40% of regular cannabis users suffer from cough, excess sputum, wheezing, and shortness of breath. A thousand young adults were followed for years, and in those who kept smoking, their respiratory symptoms got worse, or remained the same. But, those that quit tended to get better.

If we don’t quit, what are the long-term lung consequences? What about COPD (Chronic Obstructive Pulmonary Diseases), like emphysema? Even if smoking a single joint compromises lung function as much as up to five cigarettes, you’re still smoking 15 times less overall, and so, should end up with less long-term lung damage, right? That is, indeed, what’s been found.

Even long-term pot smokers don’t appear to suffer lasting lung damage. Follow people for 20 years, and an occasional joint appears to have no discernible effect on long-term lung function, though there may be some “accelerated decline” in function among those smoking joints every day for decades, and so marijuana “moderation” is suggested.

In other words, “a caution against regular, heavy marijuana usage is prudent.” But “even regular heavy use of marijuana [is nothing] compared with the grave pulmonary consequences of tobacco.” “Any toxicity of marijuana pales when compared with the greatest legalized killer in the world today.” In fact, the greatest risk to our lungs from marijuana may be that it can be a “gateway” drug to cigarettes.

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Image credit: Heath Aleike via Flickr. Image has been modified.

Motion graphics by Avocado Video.

• cigarettes
• COPD
• emphysema
• inflammation
• lung health
• marijuana
• respiratory infections
• smoking
• tobacco