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Marijuana laws in the United States have been changing rapidly in recent years. The drug is now fully legal in 16 states plus Washington, D.C. Most other states have decriminalized it, permitted it for medicinal use, or both.
With marijuana cleared for medical use in so many states, some people may wonder about its medical properties and if it can help people with different kinds of illnesses. Qualifying conditions for medical marijuana — which vary from state to state — include:
People may also wonder if there are medical conditions for which marijuana would do more harm than good. This leads to a common inquiry: Can smoking marijuana actually cause lung cancer?
The existing research is inconclusive about the link between marijuana smoking and lung cancer, so researchers will need to continue investigating before we have a final answer. However, the research up to this point has determined that smoking marijuana can cause the same types of lung damage as smoking cigarettes.
Marijuana smoke contains carcinogens, sometimes in more significant quantities than those found in cigarettes. According to the National Institute on Drug Abuse, marijuana smoke contains 50 percent more benzoprene and 75 percent more benzanthracene than cigarette smoke, as well as more nitrosamines, phenols, reactive oxygen species, and vinyl chlorides.
The way that marijuana is smoked can cause lung damage: The smoke is inhaled more deeply than that of cigarettes and held in the lungs for longer. Research has found marijunana cigarettes may contain more tar — which can cause lung damage — than cigarettes. On the other hand, marijuana users may smoke less frequently than those who smoke cigarettes.
There is no conclusive medical consensus linking smoking marijuana and lung cancer. Small, uncontrolled studies have found that smoking marijuana regularly may increase the risk of respiratory cancer. However, many population studies have not conclusively made that connection.
This discrepancy in research findings may stem from the fact some marijuana smokers also smoke cigarettes. This makes it difficult to determine how much lung damage was caused by marijuana and how much was caused by cigarettes.
Studies on animals and cell cultures have shown that tetrahydrocannabinol (THC) and cannabidiol (CBD) – both active ingredients found in cannabis – may have antitumor effects.
Though smoking marijuna may or may not cause lung cancer, there are other health implications to consider. According to the American Lung Association, smoking marijuna can:
Regardless of the status of one’s immune system, smoking marijuana can damage the lungs. Thus, the American Lung Association’s position is that people should avoid smoking marijuana entirely. “Due to the risks it poses to lung health, the American Lung Association strongly cautions the public against smoking marijuana as well as tobacco products,” the association advises.
A case-control study of lung cancer in adults 55 years of age and younger was conducted in eight sites in New Zealand. The goal was to shed light on the risk of lung cancer associated with smoking cannabis. According to the study, New Zealand has a high rate of cannabis use and one of the highest lung-cancer rates in the world, particularly among its indigenous Maori population.
The study included 79 people with lung cancer, 16 people with small cell cancer, and 63 with non-small cell cancer. For the study, cannabis smokers were defined as anyone who had smoked 20 or more marijuna joints in their lifetime. One joint was considered equal to 20 cigarettes in terms of its risk of causing lung cancer.
The study found that for each "joint-year" of cannabis exposure, a person's risk of lung cancer increased by 8 percent. Overall, smoking two joints per day resulted in abnormalities in the sputum (mixture of mucus and saliva coughed up), similar to those who smoke 20 to 30 cigarettes a day. Cannabis smoke was also found to have higher concentrations of carcinogens than cigarette smoke.
Cannabis users are not limited just to smoking. Other methods, such as vaping or edibles, allow the user to ingest cannabis while avoiding the smoke altogether. But like smoking marijana, these other methods have potential risks.
Vaping entails inhaling vapor through an e-cigarette. A 2015 study published in the Canadian Journal of Respiratory Therapy stated, “Vaporization of cannabis is likely less harmful than smoking” and “Vaporizers show promise for cannabis users who want to avoid pulmonary problems and prefer a more rapid onset than edibles provide.”
However, the study also cautioned, “Researchers have yet to gather some of the most necessary data regarding the topic.”
“There have been no published randomized clinical trials investigating vaporization with long-term follow-up,” the study concluded. “Therefore, drawing firm conclusions about the impact of the technique is difficult.”
In 2019, the Centers for Disease Control and Prevention (CDC) reported a spike in emergency-room visits for lung issues related to e-cigarette products. Sample testing showed that THC products — particularly from informal sources including friends, family, and online dealers — played a significant role in the outbreak. The CDC also found vitamin E — an additive used in THC-containing e-cigarettes — can interfere with normal lung functioning when inhaled.
Both the CDC and the U.S. Food and Drug Administration recommend people avoid using THC-containing vaping products, particularly from informal sources. Additionally, per the CDC, “THC use has been associated with a wide range of health effects, particularly with prolonged frequent use. The best way to avoid potentially harmful effects is to not use THC-containing e-cigarette, or vaping, products.”
Cannabis can be mixed into foods and beverages such as brownies, cookies, or tea. Consuming marijuana in this manner has the benefit of bypassing the lungs entirely, making it a better approach for people who are concerned about the health of their lungs.
However, ingesting edibles has its own risks. According to the National Institute on Drug Abuse, emergency room responders have seen a growing number of people suffer psychotic reactions after eating marijuana edibles. Such reactions are rare and are not limited to edibles. They can occur when a person eats more of an edible than is recommended, unaware that edibles can take up to an hour to take effect, compared to smoking marijuana which can take effect in minutes.
The institute also said that small children have fallen ill after ingesting edibles or other marijuna products that have been left out.
Although medical professionals are continuing to study the relationship between marijuana smoke and lung cancer, experts caution that smoking in general is likely harmful to the lungs and should be avoided entirely.
“Smoked marijuana, in any form, can harm lung tissues and cause scarring and damage to small blood vessels,” according to the CDC. “Smoke from marijuana contains many of the same toxins, irritants, and carcinogens as tobacco smoke. Smoking marijuana can also lead to a greater risk of bronchitis, cough, and phlegm production. These symptoms generally improve when marijuana smokers quit.”
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