Marijuana and Lung Cancer: Exploring the Link

As marijuana use continues to increase across the US — and become legalized in more states – understanding the potential negative health effects is paramount. However, any link between smoking marijuana and being diagnosed with lung cancer is still up for discussion, according to research conducted at the David Geffen School of Medicine at UCLA.

“As marijuana smoking prevalence increases in the United States, concern regarding its potential risks to lung health has also risen, given the general similarity in the smoke contents between marijuana and tobacco,” Donald P. Tashkin, M.D., division of Pulmonary and Critical Care Medicine said in his research, which was published in the journal Chest.

Marijuana — which is the second most commonly smoked substance in the US behind tobacco – saw a surge of usage between the years 2014 and 2015, when 12.9 percent of adults reported using it within the last year. In the same time frame, there was an increase in the percentage (from 5.1 percent to 7.6 percent) of individuals who used the substance on a daily or near-daily basis.

This increase has generated some public health concern, especially since marijuana shares some carcinogenic components with tobacco (a leading cause of lung cancer), such as phenols, aldehydes, acrolein and more.

“In view of the similarity in the smoke contents of marijuana and tobacco, the increasing usage of marijuana in our society, particularly on a daily or near-daily basis, raises concern regarding a potential link between marijuana smoking and the well-known deleterious effects of regular tobacco smoking on the lung, particularly regarding increased risks for developing COPD (chronic obstructive pulmonary disease) and lung cancer,” Tashkin wrote.

Tashkin analyzed prior studies to better understand the potential link between marijuana smoking and lung cancer. But overall, no definite conclusion could be reached.

“Several lines of evidence exist both for and against a link between marijuana smoking and lung cancer,” he said.

Evidence that supported the association included the fact that biopsies from frequent marijuana smokers had the same histopathologic epithelial abnormalities that were present in tobacco smokers. This included squamous metaplasia and cellular disorganization, which are believed to be pre-cancerous. Marijuana smokers also presented with higher levels of Ki67 and EGFR, which are the products of oncogenes. Not to mention, marijuana smoke contains benzpyrene, which Tashkin said is a “very potent human carcinogen.”

However, since many people who smoke marijuana also have a history of tobacco smoking, it has been a struggle for researchers to draw a clear line between the two.

Not to mention, previous research has shown that delta-9 tetrahydrocannabinol (THC) — the psychoactive ingredient in marijuana – can have a tumor suppressive effect in the lungs. This effect could counteract any tumor growth that marijuana smoking could promote.

“(T)he weight of evidence from well-designed, epidemiologic studies does not support the concept that habitual marijuana use in the manner and quantity in which it is customarily smoked, when adjusted for tobacco, is a significant risk factor for the development of lung cancer,” Tashkin said, noting the need for more research on the effect marijuana has on lung health.