Do Cannabis Smokers Develop Lung Cancer? – A Comprehensive Research Report

The question everyone should be asking, “Does cannabis smoking give you lung cancer” is perhaps the most important question you could ask.

In this series I’ve devoted considerable time and effort to give you a realistic picture of the true pulmonary risks associated with smoking marijuana. It is the most comprehensive article to date. I have analyzed much of the research on this subject covering data from nearly five decades.

You, dear reader, need to know exactly where you stand as far as your risk is concerned if you currently smoke marijuana because lung cancer is deadly. You do not want to increase your peril if at all possible.

Let’s face it, some in the research community are already convinced that cannabis smoking is as bad as or worse than cigarette smoking. But is this an accurate portrayal?

There is also a stubborn, yet significant, element of cognitive dissonance among many investigators. That is, their inability to accept (research) evidence that contradicts their firmly held beliefs. In this case it’s the belief that marijuana smoke is toxic. That it significantly increases the risk for bullous disease of the lungs, emphysema, chronic bronchitis, lung cancer, decreased lung function, and increased risk for pneumonias. Let’s see if there’s any truth to these accusations.


For decades investigators have tried to prove what they intuitively suspected to be true. That chronic use of cannabis increases the dangers for lung cancer, and other smoke related pathologies such as COPD, and pneumonia in a similar fashion as tobacco smoking.

Here’s their reasoning: the chronic use of tobacco has dozens of catastrophic, systemic effects. Nearly every organ system is adversely affected by tobacco. But in this discussion we will limit it to chronic obstructive pulmonary disease (COPD) and lung cancer with a brief mention of some others. COPD (emphysema and chronic bronchitis), and lung cancer are two of the most common and serious consequences of tobacco smoking. Smoking tobacco is the main cause of lung cancer and emphysema in the world. In fact, if you don’t smoke tobacco you eliminate two major disease risks altogether.


The theory tells us that tobacco and cannabis combustion by-products are basically the same, but because of the way cannabis is smoked it makes the risks greater. Therefore, smoking weed should give you lung cancer and COPD if you smoke enough-say at least one joint a day for 20-30 years. One joint per day times 30 years equals a 30 joint-year history which is considered heavy usage. Moderate usage is under that peak, say a 20 joint-year history.

Clinicians feel that cannabis smoke is worse than cigarette smoke because cannabis consumers take bigger tokes, hold the smoke longer in the lungs, smoke the joint to its oily conclusion, and generally do not use a cigarette filter for removing some of the gross accumulation of combustion tars.

Here’s the scary part. Back in the 1990’s studies were accumulating that sent some bad reverberations through the research community. Much of the information looked dreadful for cannabis smokers. The data predicted a major role for cannabis smoking and the development of lung cancer. It was not a good decade for cannabis consumers. Much of that data was derived from Dr Tashkin’s work spanning over four decades.

Compelling information such as these (below) were common. From the publication Effects of marijuana on the lung and its immune defenses by Donald P. Tashkin, M.D. UCLA School of Medicine. Secretary’s Youth Substance Abuse Prevention Initiative: Resource Papers, March 1997, Center for Substance Abuse Prevention, pp. 33-51:

– The tar phase of marijuana smoke, as already noted, contains many of the same carcinogenic compounds contained in tobacco smoke, induding (sic) nitrosamines, reactive aldehydes, and up to a 50 percent higher concentration of carcinogenic polycydic (sic) hydrocarbons, induding (sic) benz[a]pyrene (Hoffmann et al. 1975). Benz[a]pyrene, which has recently been shown to promote mutations in the p53 oncogene (Denissenko et al. 1996), is believed to play an important role in human cancer.

– One marijuana cigarette was shown by Wu and colleagues (1988) to deposit four times as much tar in the lung as a single filtered tobacco cigarette of approximately the same weight. The higher content of carcinogenic polycyclic hydrocarbons in marijuana tar and the greater deposition of marijuana tar in the lung act together to amplify exposure of the marijuana smoker to the carcinogens in the tar phase.

Together with numerous other findings Dr Tashkin finished with this:

– The evidence for the harmful consequences of marijuana smoking is preliminary and requires long-term study. In the interim, prudent advice must serve where substantial clinical evidence is lacking. Habitual marijuana use, as often as one joint per day, may result in serious pulmonary consequences. In the short term, breathing may be restricted, coughing may be increased, and resistance may be lowered to opportunistic infections of the lungs such as pneumonia. Respiratory cancer is a likely result in the long term. Heavier use of marijuana is likely to have more potent, adverse health consequences.

That was in 1997. In a more recent publication in 2005[ref]Tashkin DP. Smoked marijuana as a cause of lung injury. Monaldi Arch Chest Dis. 2005 Jun;63(2):93-100.[/ref] Tashkin notes several recent findings that shed more light on this controversial topic. He states that THC itself is a bronchodilator which in theory would be good for an asthmatic. Chronic pot smoking produces a small orbit of long-term pulmonary consequences, including chronic cough with sputum production; histopathologic evidence of widespread airway inflammation and injury; and immunohistochemical evidence of dysregulated growth of respiratory epithelial cells that may be precursors to lung cancer.

He continues that the THC content in cannabis could contribute to some of these injurious changes through its ability to augment oxidative stress, cause mitochondrial dysfunction, and inhibit apoptosis (programmed cell death). They also noted that the data is limited and inconsistent, there is no solid evidence that marijuana smoking may lead to chronic obstructive pulmonary disease or respiratory cancer.

Furthermore, Tashkin asserts that habitual use of marijuana is also associated with abnormalities in the structure and function of alveolar macrophages, including impairment in microbial phagocytosis (literally “to eat”) and killing that is associated with defective production of immunostimulatory cytokines and nitric oxide, thereby potentially predisposing to pulmonary infection (pneumonia).

Translated this means that chronic cannabis smoke acts as an irritant which over time can cause pre-cancerous changes in the cell architecture of the lungs. It also causes a certain amount of dysfunction of the pulmonary immune system, namely affecting the macrophages, that MAY increase risk for pneumonia. Macrophages, or “big eaters,” consume cellular debris and bacteria and anything else that needs removal. Macrophages are a major part of “pus” in a bacterial infection.

Fast forward to a 2014 review article by Denyse Lutchmansingh entitled, Legalizing Cannabis: A physician’s primer on the pulmonary effects of marijuana summarizes what we knew up to 2014 regarding marijuana’s pulmonary harms.

– Habitual smoking of marijuana is associated with multiple respiratory symptoms such as cough, sputum production, and wheezing .These symptoms are not significantly different from those exhibited by tobacco smokers. Furthermore, endobronchial biopsies of habitual smokers of marijuana and /or tobacco have shown that both marijuana and cigarette smoking cause significant bronchial mucosal histopathology and that these effects are additive. Although marijuana smokers have minimal changes in pulmonary function studies as compared to tobacco smokers, they may develop bullous disease and spontaneous pneumothoraces.[ref]Curr Respir Care Rep. 2014; 3(4): 200–205. Published online 2014 Oct 12.[/ref]

From the above 2 articles, and dozens more like them, we see that chronic marijuana smoking can cause some of the same cellular changes within the bronchial tree that are precursors to cancer or COPD (emphysema and chronic bronchitis). Also a new finding that’s already assumed to be causative: bullous disease of the lung. But we don’t see the significant damage to alveoli that tobacco smoking causes decades later which can lead to emphysema. Nor do we see the noted histopathologic changes transform into actual lung cancer. More on that in a moment.


The literature notes an association of pneumothorax (from bullous disease-see below) with chronic marijuana use. A pneumothorax is a hole in the lung with air in the chest, which can lead to a deflated portion of lung with symptoms such as breathlessness.

Tall, lanky, young males who smoke cigarettes are at the greatest risk for pneumothorax-especially if they like to scream at a football game or a similar event.

It’s nothing unique to pot smoking. The risk is also very small for pot smokers. The literature has only a handful of cases (ten total) of pneumothorax with concomitant cannabis use. And again they are only observations that show cannabis was associated with pneumothorax. Lastly, cannabis smokers appear to be at greater risk for bullous disease which is the development of large bubbles of air in the lung. This can lead to a pneumothorax. This is a hallmark for COPD but it is an association only, no proof of causation exists with pot smoking.

In addition to the associations listed above an interesting French publication from 2014 claims that:

– Cellular, tissue, animal and human studies, and also epidemiological studies, show that marijuana smoke is a risk factor for lung cancer. Cannabis exposure doubles the risk of developing lung cancer. This should encourage clinicians to identify cannabis use and to offer patients support in quitting.[ref]Underner M. Rev Mal Respir. 2014 Jun;31(6):488-98[/ref]

Here it appears that we have evidence showing that marijuana “causes” lung cancer, it doubles the risk. We have two camps, one is more conservative and the other like the above is more apt to conclude that cannabis “causes” lung cancer.

In response to the above article I can only say that the author, like many who accept the cannabis research baton, are using artistic license with the information. In other words they tend to exaggerate the harms or sometimes fabricate the harms. We’ll discuss these exaggerated claims and the reasoning behind them later.

Does pot smoking really double the risk of lung cancer? Is marijuana smoking a risk factor for lung cancer? No and no. No proof exists so far that pot increases the risk for lung cancer as you shall see.



Do the cellular changes documented above in the lungs of pot smokers translate into significant morbidity (disease)? Clinical and epidemiological data on chronic marijuana users provides a solid contradiction. Based on the pathologic changes seen microscopically we would expect to see many new cancers emerge from the din but we don’t. Where are all the lung cancer cases researchers predicted from the millions of new cannabis users who emerged since the 1990s when marijuana was finally accepted as a safe recreational drug?

Indeed where are they? It’s been 25 years starting with the somewhat arbitrary date of 1990. I picked 1990 since many investigators use this date as a marker for when pot smoking accelerated among populations all over the world. Twenty-five years later we should start seeing cancers if marijuana had the same toxicity profile as tobacco. But we don’t, in spite of the French publication mentioned in part one.

In their attempts to prove that pot causes lung cancer investigators kept hitting contradictions. The science (and observations) just didn’t add up to weed being a powerful carcinogen or cancer promoter. Back when cigarettes were suspected of causing lung cancer the epidemiologic data were overwhelmingly positive showing a clear and significant association between tobacco users and the development of lung cancer. We simply cannot find strong associations with weed and lung cancer in the same way.

For the last several decades scientists have made numerous attempts to show such an association but have come up short. Some investigators have accepted this fact and are now trying to unravel the mystery of why marijuana smokers do not run the same risks for lung cancer as that of cigarette smokers. Others who view marijuana with a jaundiced eye speedily conclude that pot smoking causes lung cancer. Same data, different conclusions.

It’s very odd actually. They both (tobacco and marijuana) start out with similar histopathologic cell changes in the lungs from exposure to similar “tars” of combustion. Then one (the tobacco user) goes on to develop lung cancer or COPD. However, the fate for the other user (the cannabis connoisseur) is completely different. The sum total of the evidence since the 1970s shows that the destructive pathologic processes in pot smokers never accelerates into lung cancer, COPD or even pneumonias. That’s what the data show. Unbiased observers agree on this point.

So something else must be going on that “prevents” the further development of cancer after metaplastic changes occur in bronchial tissues that are irritated from cannabis combustion by-products. Luckily for the millions of pot connoisseurs throughout the planet they are simultaneously ingesting a prospectus of potent anti-inflammatory molecules with each tooth-yellowing, tar hit. Those tiny molecules are called cannabinoids and they cure disease, not promote it.

You see the devil is in the details. This is precisely where tobacco and cannabis depart and head their separate ways. To put it differently nicotine and tobacco are toxic, cannabis and THC are not. In fact, some of the cannabinoids are also potent free radical mops and anti-inflammatory substances. These would help to inhibit the formation of cancers and other potentially serious disorders. In fact, we can agree that tobacco and cannabis smoke really are not the same at all.


Incidentally, the infamous Jack Herer (breeder of the Cannabis Cup winning varietal Jack Herer) relates his discussions with Dr Tashkin at UCLA, when he was writing his book, “The Emperor Wears No Clothes.” Herer:

I told Dr. Tashkin from 1981 to 1997 that no one gets lung cancer or any other type of cancer from marijuana because Dr. Vera Ruben [see below] and Dr. Todd Mikuriya had already each separately proven it. I had been doing research for my book since the early 1970s.

Both he and Tashkin completely disagreed with each other. Herer insisted that he (Tashkin) would never find proof that marijuana causes any cancer much less lung cancer. Jack may have been right all along as we will see. He finished with this amusing quote:

“If you want to live longer, smoke more pot (Jack Herer July 4, 2006)”

Maybe that should read EAT more pot and rid yourself of combustion by-products altogether.

Well, as they say that was Zen, this is Dao. Much has changed over the decades. The most recent findings from several large epidemiologic studies covering decades of pot smoking provide an anxiety-relieving golden parachute for chronic pot users. It’s good news for marijuana smokers everywhere.


Remember Quicksilver Messenger Service’s 1971 hit song, Fresh Air? You remember it don’t you? Back when songs weren’t sexed up by corporate suits, it goes like this: “[h]ave another hit of fresh air,” with much oohing before the lyrics. Well, they could have been talking about pot smoke since it looks like the miasma from marijuana is nearly as safe as pine-swept, mountain air. Yes, it sounds a little over-the-top but the latest, and best quality research has exonerated weed as a cause of smoke related (cigarette-type) pathologies. From Tashkin (2013):

– Although marijuana smoke contains a number of carcinogens and cocarcinogens, findings from a limited number of well-designed epidemiological studies do not suggest an increased risk for the development of either lung or upper airway cancer from light or moderate use, although evidence is mixed concerning possible carcinogenic risks of heavy, long-term use… In summary, the accumulated weight of evidence implies far lower risks for pulmonary complications of even regular heavy use of marijuana compared with the grave pulmonary consequences of tobacco.[ref]Tashkin DP1 Effects of marijuana smoking on the lung. Ann Am Thorac Soc. 2013 Jun;10(3):239-47. [/ref]

Meanwhile, we already have powerful epidemiologic studies on ganja smoking Rastafarians in Jamaica published by Dr Vera Rubin over 40 years ago.

– Another foreign investigation (Ruben et al., 1972) conducted in Jamaica (under contract for the National Institute of Mental Health) studied chronic cannabis users and matched nonuser controls. Preliminary findings have shown little evidence of significant differences between the two groups in the extensive anthropological, medical, psychiatric and psychological investigations.[ref]( 08/08/2015[/ref]

Honestly, if you were going to TRY to find a significant association between cannabis consumption and lung cancer, you could not do better than to study Jamaica’s Rastafarians. As a cultural phenomenon they are nearly weaned on cannabis from day one. As adults they smoke marijuana all day long every day as a means to work more efficiently, relieve heat illness and as part of their religious observations. If they are not at increased risk for lung cancer I think we can safely assume the average pudgy, joint-toking businessman isn’t either.


This just in: chronic marijuana smokers run a negative risk for lung cancer and COPD says prominent UCLA pulmonologist in 2015. From an interview with Dr. Donald Tashkin, professor emeritus of medicine at UCLA, for the LA Weekly:

– Through my studies, we failed to find any positive association. Instead, the association would be negative, between lung cancer and the use of marijuana. The likelihood is, that despite the fact that marijuana smoke contains carcinogens, we don’t see the same heightened risks of cancers that we see in tobacco.[ref][/ref]

One of the most significant diseases to emerge from cigarette smoking besides lung cancer is emphysema and chronic bronchitis; both are forms of chronic obstructive pulmonary disease (COPD). Dr Tashkin:

– The other major impact of tobacco smoking on the lungs is the association between smoking tobacco and the development of destructive pulmonary disease [such as COPD], the third cause of death in America.

…smoking marijuana, unlike smoking tobacco, does not cause chronic obstructive pulmonary disease (COPD). Reasoning for this may be that marijuana is a potent anti-inflammatory and suppressive. But COPD is activated by tobacco smoke and other toxic substances.

The National Institute on Drug Abuse (NIDA) supported Tashkin’s cannabis-related research over the decades. Tashkin initially set out to prove that pot smokers are at a significantly increased risk for lung cancer. They readily gave him a grant to conduct a large, population-based, case-controlled study that would substantiate the claim that heavy, long-term marijuana use increases the risk of lung and upper-airway cancers. What Tashkin and his colleagues found, however, sent ripples through the agenda-driven corridors of this institute.

From Rasta Livewire Fred Garner (editor of O’Shaughnessy’s) includes a story that ran initially in O’ Shaughnessy’s in 2005 when Dr Tashkin released findings at the 2005 meeting of the International Cannabinoid Research Society. This blockbuster study was ignored by NIDA, and everyone else. It eventually was published in the October 2006 issue of Cancer Epidemiology Biomarkers & Prevention.

It states rather clearly that marijuana protects people from developing airway cancers.

– As to the highly promising implication of his own study -that something in marijuana stops damaged cells from becoming malignant- Tashkin noted that an anti-proliferative [anti-cancer] effect of THC has been observed in cell-culture systems and animal models of brain, breast, prostate, and lung cancer. THC has been shown to promote known apoptosis (damaged cells die instead of reproducing) and to counter angiogenesis (the process by which blood vessels are formed -a requirement of tumor growth). Other antioxidants in cannabis may also be involved in countering malignancy, said Tashkin.[ref]( 08/09/2015[/ref]

Wait just a minute, it gets better. As mentioned earlier besides lung cancer tobacco smokers risk developing COPD. A separate study looked at lung function (a way to quantify lung damage from COPD) among cannabis and tobacco smokers. Lung function tests are the type that you see at the bedside with a patient blowing into a device with a tiny ball in it. Or it can be much more technical with computer driven machines that measure a multitude of pulmonary functions. Tashkin reports that, as predicted, tobacco-only smokers had accelerated rates of lung function decline. The more tobacco smoked the greater the rate of decline. Nothing new there.

Here’s the interesting part: pot smokers with or without concomitant tobacco use, suffered NO DECLINE in lung function. They stayed on the same trajectory as non-smokers. Dr Tashkin:

– In contrast, no matter how much marijuana was smoked, the rate of decline was similar to normal. Tashkin concluded that his and other studies do not support the concept that regular smoking of marijuana leads to COPD.

In other words your lung volumes will stay at normal, healthy values no matter how much weed you smoke. That’s fascinating, and it really says all that we need to know. Tobacco and cannabis are about as different as you can get.


We have compelling data which has accumulated for over 45 years, but in particular over the last two decades, that even heavy cannabis smoking does not increase your risk for head and neck (previous articles) or lung cancers. Furthermore, the data substantiating increased risk for developing COPD, bullous disease (and pneumothorax), or of reducing lung function from smoking pot (or pot mixed with tobacco), is either poor quality or non-existent.

This is particularly important because some researchers are already assuming these harms are true in their introductions in scientific papers. Up to as recently as 2014 many authors have already concluded wrongly that marijuana smoking causes lung cancer, upper airway cancers, bullous disease and pneumothorax, and COPD where no quality evidence permits these drastic, sweeping conclusions.


Dr Carol Tan’s wise observations and comments provide a much-needed breath of fresh air far from the madding crowd. In her Royal Society publication she highlights the bandwagon argumentative fallacy that seems particularly strong regarding marijuana harms, i.e., that pot smoking increases the risk for numerous pulmonary complications such as those listed throughout this paper.

For example, in her publication Bullous disease of the lung and cannabis smoking: insufficient evidence for a causative link[ref]Carol Tan. J R Soc Med. 2006 Feb; 99(2): 77–80. [/ref], she takes to task the chicken littles yowling that pot smoking is a cause of bullous disease of the lung, called bong lung. (I have a separate series of articles coming out that explain in detail bong lung.)

She judiciously informs us:

– Cannabis smoking appears on teaching slides as a cause of bullous lung disease and consequent pneumothorax. This seems to have become received wisdom—`A striking feature of cannabis smoking is that it is associated with bullous lung disease in young people’ (BMJ 2003;326: 942-3). The authors cite a report of four cases (Thorax 2000;55: 340-2 ). The suggestion appears, albeit in more muted terms, with the same citation in a UK Parliamentary memorandum on adverse effects of smoking marijuana on lung health (Memorandum 59. London: Royal College of Physicians, 2005).

– …Association can easily be interpreted as cause and effect particularly by a mind primed by the literature.

– …The phrase `a striking feature’ with reference to lung bullae is a strong assertion to be referenced only to a report of four patients. Co-authors, reviewers and editors generally provide a series of safety nets to protect us from overstatement but perhaps when sex, drugs and rock and roll are involved, titillation clouds reason.

– …It is of great concern that this belief about cannabis and lung bullae should have gained such wide acceptance without the production of better evidence. Perhaps myths are more easily made than forgotten.

Dr Tan’s comments focus on bullous disease from pot smoking but they could just as easily have been referring to lung cancer, COPD, psychosis, or heart attack. These sweeping assertions, based on flimsy associations from weak epidemiologic studies, condemn marijuana without sufficient scientific backing or foundation.

Many authors, as in the Dr Tan example above, seem to have drunk deeply from their institution’s Kool-Aid. The flavor of Kool-Aid in these hallowed halls often times reads “weed is a drug of abuse, it’s no good.”

Look, the information regarding marijuana harms is often times ambiguous enough without us needing to question agenda-driven conclusions from mildly hysterical clinicians. I believe this is due to a cultural anti-marijuana bias within the minds of some investigators. From my research it looks as if perhaps 50% of the publications seem to promote overstatement in regards to potential harms from chronic marijuana use.

In other words some authors may have a deeply held preconception that pot needs to look bad and appear dangerous regardless of where the science takes you. Because of this prejudice we can be terribly mislead. If I were to simply accept the exaggerated claims especially in the introductions and conclusions of many publications, I might have a completely different impression of marijuana. But it would be the wrong one.

Let’s stop the scare mongering from many in the research community. Instead observe the details of the best quality studies provided above authored by unbiased investigators like Dr Tashkin. Then we start to see a picture emerge that special properties of marijuana’s constituents-the phytocannabinoids-appear to vigorously prevent the conversion of toxic, combustion by-products, into either a cancerous lesion, bullous disease, or into the broad alveolar destructiveness of COPD.

Now isn’t it nice to know that in spite of very serious efforts to throw pot users, and the emerging worldwide legalization effort under the bus, there exists scanty evidence that marijuana causes serious pulmonary harms.

Tobacco smoking, on the other hand, is a toxic and dangerous habit. If you are living in Europe (as opposed to the US) then you probably smoke tobacco with your hash or cannabis. That’s a habit that probably should be abandoned knowing what we now know about these two popular recreational herbs.