An area of special concern is whether, like tobacco smoke, cannabis smoke is associated with increased risk of lung cancer (discussed in more detail below). This issue remains controversial, partly due to the inherent difficulty in studying an illegal substance. Because of cannabis’ status as a Schedule I controlled substance
in the U.S., it is much harder to conduct the large-scale, high-quality studies needed to fully assess its health impacts. Below is a broad overview of what is known about the effects of cannabis smoke on cardiovascular and lung health.
Secondhand Cannabis Smoke Exposure and Cardiovascular Function
Cardiovascular function is compromised by smoke inhalation of any kind. Recent research has demonstrated that secondhand exposure to cannabis smoke probably impairs cardiovascular function even more than secondhand tobacco smoke. Secondhand smoke exposure impairs blood vessels’ ability to dilate. While this has been known for secondhand tobacco smoke exposure for many years, it was only recently demonstrated to be true for secondhand cannabis smoke. Moreover, this cardiovascular impairment lasts longer for secondhand cannabis smoke.
It is important to emphasize that the negative effects on cardiovascular function come from the smoke produced by combustion of plant material and not from inhalation of plant cannabinoids such as THC or CBD
. The cardiovascular impairment described above is observed even when all cannabinoids are removed from the cannabis. Because the smoke produced by combustion will always contain toxins and carcinogens, alternative methods of consumption, such as ingestion
, should be considered if one wishes to minimize negative health outcomes.
Smoking’s Effect on Respiratory Health and Lung Cancer
An extensive literature has documented that tobacco smoke inhalation is strongly linked with increased risk of lung and other cancers. In contrast, there are many fewer studies examining these links with cannabis smoke, which prevents us from drawing definitive conclusions about cannabis smoke and cancer risk. Nonetheless, the accumulated evidence so far suggests that the risk of lung-related negative health outcomes is far lower for cannabis smoke as compared to tobacco smoke. The reasons for this may have to do with differences between the constituents of tobacco versus cannabis smoke.
Cannabis smoke is like tobacco smoke in that both contain a high number of carcinogens produced by combustion. Certain carcinogens are actually present at higher levels in cannabis smoke compared to tobacco smoke, and cannabis smokers tend to inhale more deeply and hold in smoke for longer durations. Both observations would lead one to expect, if anything, a greater risk of lung cancer for cannabis smoke exposure compared to tobacco smoke. However, this is not the case; a limited number of well-designed epidemiological studies have failed to find an association between cannabis and increased risk for lung cancer. This apparent paradox may be explained by other differences in the composition of cannabis and tobacco smoke.
Cannabis smoke is different from tobacco smoke in that some of its constituents, like the plant cannabinoids THC and CBD, are non-carcinogenic and demonstrate anti-cancer and antioxidant properties. This may explain why several studies have shown no significant link between cannabis smoke and respiratory cancer (at least for light to moderate cannabis smokers). However, there is mixed evidence on cancer risks for heavy, long-term smokers. A few studies have reported an association between cannabis use and upper airway or lung cancer, but these have come from small case-control studies that suffered from methodological flaws, such as not controlling for tobacco use. More large-scale studies with rigorous methodologies are needed.
Assessing the effects of smoking cannabis on cancer risk is particularly difficult because cannabis consumption and tobacco use are correlated; the highest-quality studies are those that draw from large samples of individuals and a control for confounding factors such as tobacco use and other variables. While the small number of well-designed population-based studies that have been conducted have generally failed to find an association between cannabis use and lung or upper airway cancer, more high-quality research is sorely needed. Cannabis’s status as a federally illegal substance makes this difficult to achieve in a timely fashion.
Respiratory Damage and Infection from Smoking
Another key way that that cannabis differs from tobacco is in its effects on the immune system. In general, cannabis has anti-inflammatory and immunosuppressive effects. This can be beneficial for patients suffering from inflammatory diseases such as inflammatory bowel disease or multiple sclerosis. On the other hand, because regular cannabis smoke inhalation causes physical airway damage, the immunosuppressive effects of cannabis may leave regular smokers more susceptible to certain respiratory infections. For example, This is also an area where a greater number of rigorous, large-scale studies would be beneficial.
Cannabis and Smoking, In Summary
A broad survey of the scientific literature leaves us with the follow list of conclusions about the health effects associated with smoking cannabis:
- Overall, the negative effects of smoking cannabis on lung health appear to be lower than for tobacco smoking.
- Cannabis smoking is associated with lung function abnormalities, but the pattern of these abnormalities is different from those associated with tobacco smoking.
- Regular cannabis smoking can cause physical airway damage, and is associated with the symptoms of bronchitis.
- Secondhand cannabis smoke exposure leads to impairments in cardiovascular function.
- There is no compelling evidence that cannabis smoking leads to obstructive airway disease of emphysema.
- A limited number of high-quality studies have failed to find a link between cannabis smoking and lung or upper airway cancers for occasional or moderate consumers.
- There is mixed evidence for increased cancer risk in heavy, long-term cannabis smokers.
- More research, especially on whether smoking cannabis can lead to lung or other cancers, is desperately needed.
- Alternative methods of cannabis consumption, such as vaporization, do not carry many of the risks associated with smoke inhalation.
Gates P, Jaffe A, Copeland J. Cannabis smoking and respiratory health: consideration of the literature. Respirology. 2014;19(5):655-62.
Lee MHS & Hancox RJ. Effects of smoking cannabis on lung function. Expert Review of Respiratory Medicine. 2011;5(4):537-547.
Naeher LP, Brauer M, Lipsett M, et al. Woodsmoke health effects: a review. Inhal Toxicol. 2007;19(1):67-106.
Tashkin DP. Effects of marijuana smoking on the lung. Ann Am Thorac Soc. 2013;10(3):239-47.
Wang X, Derakhshandeh R, Liu J, et al. One Minute of Marijuana Secondhand Smoke Exposure Substantially Impairs Vascular Endothelial Function. J Am Heart Assoc. 2016;5(8)