While trying to find one study about carcinogenic properties in marijuana and nicotine, I went down a rabbit hole and found the following research articles and summaries from various sources. You can click on the title to go to the article itself. Keep reading to find out what happened next! 

From The American Lung Association:
“Marijuana And Lung Health”

Marijuana Smoke
Smoke is harmful to lung health. Whether from burning wood, tobacco or marijuana, toxins and carcinogens are released from the combustion of materials. Smoke from marijuana combustion has been shown to contain many of the same toxins, irritants and carcinogens as tobacco smoke.4-7

Beyond just what’s in the smoke alone, marijuana is typically smoked differently than tobacco. Marijuana smokers tend to inhale more deeply and hold their breath longer than cigarette smokers, which leads to a greater exposure per breath to tar.8

Secondhand marijuana smoke contains many of the same toxins and carcinogens found in directly-inhaled marijuana smoke, in similar amounts if not more.5 While there is no data on the health consequences of breathing secondhand marijuana smoke, there is concern that it could cause harmful health effects, especially among vulnerable children in the home. Additional research on the health effects of secondhand marijuana smoke is needed.

Medical Marijuana
The American Lung Association encourages continued research into the health effects of marijuana use, as the benefits, risks and safety of marijuana use for medical purposes require further study. Patients considering using marijuana for medicinal purposes should make this decision in consultation with their doctor, and consider means of administration other than smoking.

***I boldened this part because I agree with and like what they said, as it seems like a balanced and unbiased approach.***

Bottom Line
-Smoking marijuana clearly damages the human lung, and regular use leads to chronic bronchitis and can cause an immune-compromised person to be more susceptible to lung infections.
-No one should be exposed to secondhand marijuana smoke.
-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.
-More research is needed into the effects of marijuana on health, especially lung health.


Effect of cannabis smoking on lung function and respiratory symptoms: a structured literature review


This review clearly shows that chronic marijuana smoking is associated with respiratory symptoms and increase in FVC. The mechanisms for these effects and the differences from the effects of tobacco remain unclear. More work needs to accurately measure cannabis use as well as measure all aspects of respiratory health, particularly breathlessness and exercise tolerance. More importantly, however, there needs to be larger, longer-term studies with marijuana smokers who do not smoke tobacco.

There is clear evidence that marijuana causes similar symptoms to tobacco smoking (chronic bronchitis) and produces similar large airway pathological features. There is some evidence that the combination of tobacco and marijuana is additive. Tobacco unequivocally causes chronic airflow obstruction and COPD but only in a minority of smokers. Cannabis smoking, however, produces an increase in FVC and the reason(s) for this are unclear and require elucidation. Taking a more detailed history with regard to cannabis smoking and other illicit inhalational drugs should be part of the standard respiratory assessment of all patients, which would also support better epidemiological data collection for future studies, particularly in the primary care population.


The Impact of Cannabis On Your Lungs

Published research shows:
• a link between smoking cannabis and many respiratory
problems, including chronic coughing, sputum
production and wheezing;
• a connection between smoking cannabis and infective
lung conditions such as tuberculosis (TB) and
legionnaires’ disease
• a link between smoking cannabis and collapsed lung
• stronger evidence than ever before that smoking
cannabis is linked to lung cancer;
• a lack of conclusive evidence on how smoking just
cannabis (i.e., without tobacco) affects lung function and
the development of chronic obstructive pulmonary
disease (COPD), and
• smoking both tobacco and cannabis appears to lead to
a greater risk of COPD and pneumothorax than smoking
a similar amount of tobacco alone.
We believe more investment is urgently needed to find
out the true effects of smoking cannabis on respiratory
health. We especially need to know more about the
impact smoking cannabis has on lung function and
COPD risk.




There were 79 cases of lung cancer and 324 controls. The risk of lung cancer increased 8% (95% CI 2% to 15%) for each joint-year of cannabis smoking, after adjustment for confounding variables including cigarette smoking, and 7% (95% CI 5% to 9%) for each pack-year of cigarette smoking, after adjustment for confounding variables including cannabis smoking. The highest tertile of cannabis use was associated with an increased risk of lung cancer RR=5.7 (95% CI 1.5 to 21.6), after adjustment for confounding variables including cigarette smoking.


Long term cannabis use increases the risk of lung cancer in young adults.


What Are Marijuana’s Effects On Lung Health?

Like tobacco smoke, marijuana smoke is an irritant to the throat and lungs and can cause a heavy cough during use. It also contains levels of volatile chemicals and tar that are similar to tobacco smoke, raising concerns about risk for cancer and lung disease.67

Marijuana smoking is associated with large airway inflammation, increased airway resistance, and lung hyperinflation, and those who smoke marijuana regularly report more symptoms of chronic bronchitis than those who do not smoke.67,68 One study found that people who frequently smoke marijuana had more outpatient medical visits for respiratory problems than those who do not smoke.69 Some case studies have suggested that, because of THC’s immune-suppressing effects, smoking marijuana might increase susceptibility to lung infections, such as pneumonia, in people with immune deficiencies; however, a large AIDS cohort study did not confirm such an association.67 Smoking marijuana may also reduce the respiratory system’s immune response, increasing the likelihood of the person acquiring respiratory infections, including pneumonia.68 Animal and human studies have not found that marijuana increases risk for emphysema.67


    I found this article that seemed to be at odds with the other articles I found, so I looked up the person who wrote it/researched.  Here’s an article I found about him:

Cannabis Advocate and Researcher ‘Dr. Bob’ Melamede Dies at 75.

Here’s the conclusion from his research article:

Cannabis and Tobacco Smoke are Not Equally Carcinogenic
By Robert Melamede

In conclusion, while both tobacco and cannabis smoke have similar properties chemically, their pharmacological activities differ greatly. Components of cannabis smoke minimize some carcinogenic pathways whereas tobacco smoke enhances some. Both types of smoke contain carcinogens and particulate matter that promotes inflammatory immune responses that may enhance the carcinogenic effects of the smoke. However, cannabis typically down-regulates immunologically-generated free radical production by promoting a Th2 immune cytokine profile. Furthermore, THC inhibits the enzyme necessary to activate some of the carcinogens found in smoke. In contrast, tobacco smoke increases the likelihood of carcinogenesis by overcoming normal cellular checkpoint protective mechanisms through the activity of respiratory epithelial cell nicotine receptors. Cannabinoids receptors have not been reported in respiratory epithelial cells (in skin they prevent cancer), and hence the DNA damage checkpoint mechanism should remain intact after prolonged cannabis exposure. Furthermore, nicotine promotes tumor angiogenesis whereas cannabis inhibits it. It is possible that as the cannabis-consuming population ages, the long-term consequences of smoking cannabis may become more similar to what is observed with tobacco. However, current knowledge does not suggest that cannabis smoke will have a carcinogenic potential comparable to that resulting from exposure to tobacco smoke.

It should be noted that with the development of vaporizers, that use the respiratory route for the delivery of carcinogen-free cannabis vapors, the carcinogenic potential of smoked cannabis has been largely eliminated [,].

This lead me down another rabbit hole with the question of: Melamede died from a stroke and other complications.  He smoked marijuana for many, many years.  Is it possible that chronic marijuana use can lead to stroke? Here’s what I found:

Cannabis Use and Stroke: Does a Risk Exist?

Conclusions: In people with cannabis use, the prevalence of ischemic stroke and hemorrhagic stroke was 1.2% and 0.3%, respectively, higher than the prevalence of people without use (0.8% and 0.2%). There is insufficient information on timing, exposure, duration, and dose-responsive relationship.

Young Marijuana Smokers May Be At Greater Risk of Recurrent Stroke

Research Highlights:

  • Among hospitalized adults, ages 18-44 who had a history of stroke or transient ischemic attack (TIA), the cause of another hospitalization was 48% more likely to be another stroke if they were habitual marijuana smokers.
  • According to previous research, problematic marijuana use has already been associated with an increased risk of an initial stroke, however, this is the first study to suggest that recurrent stroke may also be more likely.
  • Since recreational marijuana use is legal in numerous states in the U.S., understanding the impact of habitual use on cardiovascular health is important.


In my opinion,  this following article is a great statement made by the AHA.  I liked how they went into science and research of it, the different properties of marijuana and how said properties affect the body differently (some harmful, some not harmful).  There’s a lot I wanted to copy/paste here, but here’s one paragraph (click on the title to read the full statement): 

Medical Marijuana, Recreational Cannabis, and Cardiovascular Health: A Scientific Statement From the American Heart Association

“Cannabis smoke contains many of the same carcinogens and mutagens as tobacco smoke.5,12,20 In addition, cannabis smoking is associated with a variety of histopathological changes in respiratory tissues, similar to those in tobacco smokers. However, limited and conflicting evidence from epidemiological studies has not shown a robust and consistent association between cannabis use and various types of cancer.52 Low-strength evidence suggests that smoking marijuana long term may be associated with the development of testicular cancer. Findings for lung cancer are mixed and confounded by few marijuana-only smokers, poor exposure assessment, and inadequate adjustment within studies.52 The association between long-term heavy cannabis smoking (without tobacco) and chronic obstructive pulmonary disease remains unclear; however, chronic bronchitis has been reported.5,12

Finally, with the worldwide pandemic of coronavirus disease 2019 (COVID-19) caused by the novel coronavirus severe acute respiratory syndrome coronavirus 2, tobacco smokers appear to be more likely than nonsmokers to have severe symptoms of COVID-19 (relative risk, 1.4 [95% CI, 0.98–2.00]) and much more likely to be admitted to an intensive care unit, to need mechanical ventilation, or to die (relative risk, 2.4 [95% CI, 1.43–4.04]).53 Whether this risk also extends to smoking or vaping cannabis is not known.”

Here’s more related research articles:

Marijuana Use and the Risk of Early Ischemic Stroke

Marijuana’s effects on the brain need more research

Recurrent stroke associated with cannabis use

Overall, the recurring statement in these research articles is: MORE RESEARCH NEEDS TO BE DONE.  The medical use of marijuana is so new that long-term research doesn’t exist yet, plus the marijuana we use today is vastly different compared to the marijuana used in the 60’s and 70’s.  A blanket approach and fast push in making it readily available to the public in so many different forms without solid research of its effects on us, in my opinion, is dangerous and could do more harm than good.  I’d like to see legislation that upholds the true medical side of marijuana and allows law enforcement to rigorously uphold the law so it won’t be abused as we see now with the current medical marijuana law in South Dakota.