Cigarette smoking is far and away the No. 1 risk factor for developing chronic obstructive pulmonary disease — a progressive, incurable lung disease that makes it harder to breathe over time. The Centers for Disease Control and Prevention reports that “smoking accounts for as many as 8 out of 10 COPD-related deaths.” A 2010 report from the Surgeon General, ” How Tobacco Smoke Causes Disease,” indicates that the vast number of chemicals and toxins that are drawn into the lungs when smoking can cause damage to cells in the lungs, which in turn leads to an increase in oxidative stress and inflammation. This damage and associated inflammation can build up over time and develop into emphysema or chronic bronchitis, the two primary diseases that fall under the COPD diagnosis umbrella.
[See: 7 Things You Didn’t Know About Lung Cancer.]
Although it contains many of the same toxins and chemicals as cigarettes, marijuana smoke hasn’t been conclusively linked to lung damage the way cigarettes have. Still, “marijuana smoke contains most of the toxins that tobacco smoke contains, so it’s reasonable to be concerned that marijuana smoke might be toxic to the lungs,” says Dr. Russell Bowler, professor of medicine and director of the COPD clinic at National Jewish Health in Denver. This has led some scientists to investigate whether smoking marijuana can cause COPD.
Among these researchers is Dr. Donald Tashkin, emeritus professor of medicine at the David Geffen School of Medicine at UCLA. He has studied the interaction between marijuana and the lungs for some 40 years, producing several studies examining whether marijuana increases risk for pulmonary disease while also looking at whether it could potentially be used as a treatment for COPD.
Beginning in the 1970s, Tashkin learned that “smoking marijuana actually dilated the airways rather than constricting them. It was a significant amount of bronchodilation,” he says, caused by the compound in marijuana that’s also responsible for causing the smoker to feel “high” — tetrahydrocannabinol, or THC. “We actually pinpointed the agent that was responsible for the bronchodilation by extracting the THC from the marijuana and then reinjecting it into the placebo marijuana, which didn’t contain any THC.” He says they also administered the THC orally and observed the same airway-opening effect.
From there, he says he became interested in the long-term effects of marijuana smoking “with respect to the potential for harm to the lung. The rationale for that hypothesis was that marijuana smoking could injure the lung and possibly predispose [smokers] to COPD.” This idea was based on the knowledge that “the smoke in marijuana contains many of the same ingredients that are found in tobacco smoke, including polycyclic aromatic hydrocarbons,” which are known carcinogens (cancer causing-agents) “and a number of chemicals that are irritating to the respiratory tissue.”
Tashkin says these studies controlled for other factors including cigarette smoking and found that marijuana smoking, even among heavy users, did not seem to elevate risk for developing either COPD or lung cancer. Although a 2013 review written by Tashkin in the Annals of the American Thoracic Society noted that a few smaller studies have indicated there could be a connection between marijuana and lung cancer, the sample sizes were either too small or tobacco smoking wasn’t limited as a control factor, so a causal connection couldn’t be conclusively drawn.
The reason why marijuana may not elevate risk for lung cancer or COPD is unclear but could be related to dosage. “It’s not unusual for tobacco cigarette smokers to smoke 40 cigarettes a day,” Bowler says. There’s likely not many people who are smoking 40 joints per day, and so even heavy users of marijuana typically smoke less than the heaviest users of tobacco. “That likely explains some of the differences we’ve seen,” he says. (However, the way marijuana is typically smoked — by taking a deeper inhalation and holding the smoke in the lungs longer than in cigarette smoking — does result in higher concentrations of carbon monoxide and tar in the respiratory tract.)
[See: 16 Ways Your Body Adjusts to a New Climate.]
Another theory, Tashkin says, is that THC has an immunosuppressant effect that deactivates certain immune cells in the lungs, called alveolar macrophages. This effect may curb the hallmark inflammation of COPD, “so we believe that may be the reason that marijuana smokers don’t develop the changes we see in COPD in tobacco smokers.” He notes that THC also has some anti-tumor properties that could explain why marijuana smoking doesn’t appear to elevate risk for developing lung cancer, although some limited research has indicated there could be a connection between marijuana use and testicular and prostate cancers. “I think the data are mixed on lung cancer,” Bowler says. “There has not been really conclusive evidence that marijuana smoking is related to lung cancer.”
Despite the fact that it doesn’t appear to elevate risk of developing COPD, Bowler says “there are lots of studies including some of mine that have shown there is increased risk of chronic bronchitis symptoms. So [marijuana smoking] is not benign. It does cause symptoms that are related to COPD,” such as increased sputum production and wheezing, “but maybe we don’t have good evidence that it causes COPD per se,” he says. Bowler co-authored a 2016 report from the Colorado Department of Public Health and Environment, ” Monitoring Health Concerns Related to Marijuana in Colorado: 2016” that presents an in-depth look at the various health effects of marijuana.
In any case, Tashkin is unequivocal when he says he “would never recommend marijuana in any form for a patient with COPD.” If, however, a hypothetical COPD patient were interested in using marijuana for another condition, such as controlling intractable pain for which other methods of alleviating symptoms have failed, a vaporized form of THC would minimize lung exposure to the toxic components of marijuana smoke. He also says that edibles are “absolutely not” a good solution in these cases, as they often contain a synthetic form of THC that’s been “manipulated to markedly increase the potency.” This can lead to dangerous side effects such as seizures and even death in some cases.
[See: 8 Surprising Facts About Asthma and Seasonal Allergies.]
The bottom line is that we just don’t really know yet exactly how marijuana affects lung health, particularly in the long run. Both Tashkin and Bowler say more research needs to be done before anyone can conclusively say whether smoking marijuana is a safe activity from the perspective of lung health. Part of the problem in determining whether marijuana is helpful or harmful is because “it’s always complicated by the fact that many marijuana smokers also smoke tobacco cigarettes. So the trick is to distinguish the effects of tobacco from the effects of marijuana smoking,” Bowler says. “I think the whole of it is that there are adverse effects associated with marijuana smoking. The flip side of that is what are the medical benefits? If we’re going to expose people to something that’s potentially risky, we should have some evidence that there are some real benefits to smoking marijuana, and I think that’s where there’s a big research deficit,” Bowler says.
More from U.S. News
7 Things You Didn’t Know About Lung Cancer
7 Lifestyle Tips to Manage Your Asthma
16 Ways Your Body Adjusts to a New Climate
Is There a Connection Between COPD and Marijuana Smoking? originally appeared on usnews.com
