No-Smoke November! Update on the Effects of Marijuana Smoke

Hello! Dr. Lee here.

I’m gearing up to hang out with our friends at Chillinois Podcast for a podcast taping and I went over some evidence to prepare. They are promoting “No Smoke November” and I for one think it’s an excellent idea.

On a personal note, I talked to a patient the other day and mentioned that I would send them a paper about the effects of marijuana on the lungs. I did, and realized that there was basically nothing but medical jargon in said paper. In my guilt I have decided to make a blog post to describe the information that we do have out here in doctor-world.

If you’ve used our service before this might sound familiar. Every single patient that uses our service is forced to listen to our discussion about how you aren’t supposed to smoke. It’s company policy! (I mean it depends which one of us you get. I’m definitely the strictest haha!)


  1. It’s hard to study marijuana because it’s federally illegal (see previous post on the War on Drugs to see why!). However, our evidence on health outcomes (the harm that marijuana smoke causes) is growing, and it’s pretty consistent.

  2. Smoking weed causes changes similar to obstructive lung disease. We know that it causes similar symptoms (such as shortness of breath and increased sputum), as well as cellular changes.

  3. We aren’t sure if smoking weed causes cancer, but we’re kind of confident that it causes lung, head/neck and testicular cancer.

  4. We aren’t sure if smoking weed has an effect on cardiovascular disease yet, but it seems like it can be associated with heart disease and stroke the same way smoking tobacco is

  5. If you are science-y and want to read something, I recommend this. It is current and thorough.


I think almost everyone starts out their marijuana career with smoked flower cannabis. I definitely did. It’s inexpensive and easy to find. For people that have used flower marijuana for a long time, it can become hard to switch to any other product.

That’s why I feel like we have to be very clear about the data we have. Smoking weed is kind of bad for you! This fact goes kind of unspoken in marijuana counseling and it’s really the most important thing for physicians to talk to their patients about.

In many aspects, such as potential for acute overdose and important drug-drug interactions, marijuana is quite benign. If we tackle the smoking issue as marijuana users, we’re dealing with what has been so far shown to be a relatively safe product.

There are specific patients that certainly shouldn’t smoke- anyone with a respiratory condition (like asthma or COPD) or a vascular condition (like coronary artery disease, or peripheral vascular disease) should be especially wary.

EVERYONE should make sure that they are incorporating products that aren’t inhaled. And if you are a flower smoker, you need to think about smoking less and switching to a healthier option

I often talk to patients about using something like a dry herb vape to mitigate the harm to your lungs. That’s actually not an evidence-based suggestion (which I usually don’t like to give) but “seems” like its the safest way to inhale.


It’s not great. There are some subsets of marijuana research that are fairly well studied, but health outcomes are not one of them.

Most of the data we have on marijuana and health outcomes is retrospective. It is basically when a researcher sits down with someone that smokes weed and asks them a bunch of questions. It’s not the best! It’s subject to bias, especially recall bias (commonly referred to as forgetting stuff).

The medical community prefers planned, prospective studies as they tell us more, and let us control more about the research process. In regards to how marijuana harms the human body, we have had several decades of low- and medium- quality studies but none of the large-scale studies that doctors really need to make decisions.

For a historical reference, compare this with tobacco. Small retrospective studies were published in the 1920s-1940s while tobacco was in its adolescence. The first well-conducted, prospective study was published in 1954- over seventy years after the tobacco industry started in the United States. The anti-smoking movement was buoyed by this research, but it STILL took a decade for the public to change its smoking ways. Cigarette consumption per-person peaked in 1965.

That first part? Where scientists were suspicious of tobacco but had no proof? That’s where we are right now with marijuana. We have somewhat half-assed data on what happens to your lungs and heart when you smoke marijuana. We have plenty of studies, but these are mostly small and medium sized studies with important flaws. Flaws in this sense are issues with the data-gathering process. Examples include depending too much on patients old memories, or using patients with only a minimal amount of marijuana exposure.

In recent years, we have had enough of these small, weak-ish studies to produce research that we call a meta-analysis. This involves a bunch of math dweebs pooling the data we do have to see if we can make any broader claims about marijuana’s effect on the human body.

In 2018, three important meta-analyses looked separately at lung function, cancer and cardiovascular disease. These publications were well-executed and published in the Annals of Internal Medicine and JAMA, which are two extremely influential medical publications (6-8). They form the basis of what we are going to discuss in the next section.


Note that even though marijuana is still illegal and fairly poorly researched, it’s still being discussed in really important medical publications. This reflects the interest that both clinicians and the public have in marijuana!

We are really far behind where we should be on marijuana research because of the War on Drugs. It’s impossible to study something with such spotty legality. Not only does it eliminate access to federal funding, it fundamentally changes the way people answer questions. How can you be completely honest about your marijuana history when it can jeopardize your employment? You can’t!

The War on Drugs is the single most important thing keeping us from knowing more about marijuana. But, there are other issues.

There is another key aspect of research that has been hard to unwind: the fact that most marijuana users have also smoked cigarettes. It’s mentioned in virtually all research on marijuana. It becomes hard to tell what health effects are attributed to which exposure.

Marijuana research has a huge standardization problem as well. What exactly is a “joint?” What weight does it have? What’s the THC content of the marijuana? Almost no studies that mention joints clarify this. The amount of THC in marijuana has been also consistently risen since marijuana was introduced to American decades ago.


GREAT QUESTION! Overall, the main takeaway is that our data is pretty shitty and that we need more research.

But, the data we DO have tells us enough to make some useful claims, and rebut some clearly incorrect old-wives-tales about marijuana.

The first myth about marijuana that I would like to dispel is that marijuana smoke is inherently different from other smoke. It is true that it does not have the additives that most cigarettes still have. But, when we really look at marijuana smoke (like with an ultra-microscope called a mass spectrometer), it contains a lot of the same compounds that we KNOW cause cancer in tobacco smoke (1-3).

Smoking, and THC, also has some pretty clear negative effects on the vasculature of the body. Did you know that smoking marijuana causes a five fold increase in carbon monoxide and three-fold increase in tar levels in the bloodstream after inhaling? (14). Because it does!

So long story short, you’re breathing in stuff that we know causes lung damage. BUT, Does that translate into getting a lung disease?


We do have pretty solid evidence that marijuana causes changes similar to COPD, but we have so far stopped short of saying that marijuana causes COPD. That link just is not clear yet.

We do have several prospective observational studies (the ones we like) that show that over time, smoking weed does cause symptoms (9-12). It indeed leads to shortness of breath, increased sputum production and histological (changes to your cells) changes in your airway similar to COPD. To be perfectly honest, those symptoms are basically chronic bronchitis, which is basically COPD. I’m pretty sure that eventually we will cement this link between marijuana smoke and COPD!

But, for whatever reason, despite containing similar compounds, marijuana smoke overall does seem to be a little less damaging than tobacco smoke. For one thing, marijuana smoke has been paradoxically shown to have modest bronchodilatory properties (opening the airway), the significance of which is unclear. We also know theorize that on a day-to-day basis, most tobacco smokers will inhale more than a marijuana smoker. So, we think that the overall volume of smoke exposure is usually greater in a tobacco smoker.

But, smoke is smoke, and going through med school you eventually realize that lungs are frail organs that are pretty much ready to turn into disease-blobs. COPD is one thing, but I feel like on a personal level, the risk of cancer is a bit more frightening.


To make a long story short, the link between marijuana smoke and cancer is unclear (7). It has been speculated to cause lung cancer for obvious reasons, but the data hasn’t shown this to be true yet. Tobacco also causes head and neck cancer (lip, tongue, throat, esophagus) and marijuana might as well, but that too hasn’t been shown yet.

Interestingly, the specific type of cancer most associated with marijuana use is…drumroll…testicular cancer! As a doctor, I have no idea what to do with this information yet. I just think it’s funny.

That might be kind of reassuring, but I would like to make one thing very clear: the amount of marijuana that users report in these studies is very low. It does not reflect the amount of marijuana that most marijuana users use. Sorry! For instance, they typically use “joint years” as a way to kind of reflect “pack years.” In tobacco years, a pack year is smoking one pack per day for a year. A joint year is…one joint per day per year. For long-time smokers, there’s no way that accurately reflects the amount of smoke exposure you have. So I think this is false reassurance.

In fact, this is one of the big issues I have with marijuana research. Again, many papers offer no system for quantifying the amount of marijuana that users consume, which just reflects the detachment that marijuana science has from marijuana-using reality. Speaking as a marijuana user…do you ever not know how much weed you have? 


Lastly, we know that tobacco smoke causes an intense change in the blood vessels of the body. It is one of the strongest risk factors for heart disease and dyslipidemia (issues with cholesterol). Since marijuana smoke and tobacco smoke contain similar compounds, marijuana smoke is theorized to cause similar changes. THC is a sympathetic activator (the fight-or-flight response)- you may have noticed a higher heart rate (tachycardia) when you smoke. The direct sympathetic effects from THC, and the blood-vessel-irritating effects of smoking are two possible reasons that marijuana smoke can be dangerous for the human heart.

One of the big questions we have is whether smoking weed can set off a heart attack or similar event, because smoking often does. Per the research journal Circluation, “Tetrahydrocannabinol stimulates the sympathetic nervous system while inhibiting the parasympathetic nervous system; increases heart rate, myocardial oxygen demand, supine blood pressure, and platelet activation; and is associated with endothelial dysfunction and oxidative stress. (13)” So our best guess is, yes. There’s also some a couple of case reports that young patients can have isolated myocardial infarctions or bouts of atrial fibrillation after heavy marijuana consumption (14, 15).

Does marijuana cause stroke? Does it cause heart disease? The data doesn’t show anything definitive yet (8). But, there has been some positive associations between marijuana smoke and developing a stroke (14). Lifetime risk of stroke or TIA is increased in marijuana users. There’s also a troubling weird spike in strokes in young patients (aged 18-44) in patients that smoke both tobacco AND marijuana (16)!

So I would use my big brain and say YES! Marijuana is a risk factor for cardiovascular disease. Not a slam dunk yet but the writing is on the wall.


I always tell my doctor friends that, if they don’t use or like marijuana, they still need to learn about it because so many of their patients will use it in the future.

I think there’s a looming public health issue in the upcoming years due to the tremendous number of marijuana users and the lack of information that we have about their health outcomes. Thanks, War on Drugs!

A multi-billion dollar marijuana industry that is federally illegal and poorly researched is just a shit-show and the government should be properly shamed until Mom and Dad (Kamala and Joe) finally end this nonsense.

I also foresee a day in which all marijuana products are labeled with the same cancer/COPD warnings as tobacco products are.

Every marijuana user needs to get counseling about smoking that reflects current research. It’s typically not coming from a primary care physician (not their fault, we don’t incorporate marijuana in medical education).

As we learn more, doctors should have more ways to tell patients about what we do know. And what we infer- which is that smoking flower cannabis is not super-healthy and we should all try to avoid it.

Ideally, we would be able to give specific counseling- you know, replace smoked products with edibles, here’s some to try, here’s what edible products have been popular with smokers in the past (RSO). That type of thing. It takes experience with marijuana though, which is rare (and why everyone should use a specialized service wink wink).


I’ve also noticed a funny thing happening lately that was not so obvious in the past- people that want to smoke weed in the hospital but can’t. They end up sneaking out and smoking with friends/family or sneaking in a vape or something. But, this can be an issue medically! Smoking weed changes some outcomes, and we will definitely learn about more of these outcomes over time.

Here’s one example we know a decent amount about. In the post-surgical setting smoke inhalation can be detrimental, and in some specific issues like pneumothorax, marijuana smoke changes outcomes.  To give another example, young patients that receive surgery for pneumothoraces in the hospital have different outcomes on whether or not they smoke weed afterwards. Better outcomes are clearly seen in non-smoking patients.

I actually think that medical school should revamp the way they teach pneumothorax because there’s such a strong correlation between marijuana smoking and pneumothoraces. Any patient that presents with a pneumothorax should receive a thorough history on their marijuana use, which has to include the way that they smoke marijuana (since it’s particularly associated with bong-rips).

So where does this leave us? “Don’t smoke weed in the hospital! Just stop smoking it!” Yes, that’s a great attitude and it tooootally works for other addictive substances (huge /s).

I rarely stop a benzo or opiate for a hospitalized patient, because they lose their shit. It’s annyoing! We should be looking at marijuana the same way. We need to be finding strategies to incorporate marijuana research in knowledge into clinical practice.

That’s why we learn more about marijuana. That’s how “Don’t smoke weed” becomes, “use an edible product.” Which later becomes, “allow pharmacy access to high concentrate edibles like RSO to ameliorate marijuana withdrawal symptoms in hospitalized patients with marijuana dependence.”


Stop smoking so much weed.

Dr. Lee


  1. Moir D, Rickert WS, Levasseur G, Larose Y, Maertens R, White P, Desjardins S. A comparison of mainstream and sidestream marijuana and tobacco cigarette smoke produced under two machine smoking conditions. Chem Res Toxicol. 2008 Feb; 21(2):494-502

  2. Lee ML, Novotny M, Bartle KD. Gas chromatography/mass spectrometric and nuclear magnetic resonance spectrometric studies of carcinogenic polynuclear aromatic hydrocarbons in tobacco and marijuana smoke condensates. Anal Chem. 1976;48:405–16. [PubMed] [Google Scholar]

  3. Hoffmann D, Brunneman DK, Gori GB, Wynder EL. On the carcinogenicity of marijuana smoke. Recent Adv Phytochem. 1975;9:63–81. [Google Scholar]

  4. Martinasek MP, McGrogan JB, Maysonet A. A Systematic Review of the Respiratory Effects of Inhalational Marijuana. Respir Care. 2016 Nov;61(11):1543-1551. doi: 10.4187/respcare.04846. Epub 2016 Aug 9. PMID: 27507173.

  5. Stefani A, Aramini B, Baraldi C, Pellesi L, Della Casa G, Morandi U, Guerzoni S. Secondary spontaneous pneumothorax and bullous lung disease in cannabis and tobacco smokers: A case-control study. PLoS One. 2020 Mar 30;15(3):e0230419. doi: 10.1371/journal.pone.0230419. PMID: 32226050; PMCID: PMC7105102.

  6. Ghasemiesfe M, Ravi D, Vali M, Korenstein D, Arjomandi M, Frank J, Austin PC, Keyhani S. Marijuana Use, Respiratory Symptoms, and Pulmonary Function: A Systematic Review and Meta-analysis. Ann Intern Med. 2018 Jul 17;169(2):106-115. doi: 10.7326/M18-0522. Epub 2018 Jul 3. PMID: 29971337; PMCID: PMC6231497.

  7. Ghasemiesfe M, Barrow B, Leonard S, Keyhani S, Korenstein D. Association Between Marijuana Use and Risk of Cancer: A Systematic Review and Meta-analysis. JAMA Netw Open. 2019 Nov 1;2(11):e1916318. doi: 10.1001/jamanetworkopen.2019.16318. Erratum in: JAMA Netw Open. 2020 Jan 3;3(1):e1921065. PMID: 31774524; PMCID: PMC6902836.

  8. Ravi D, Ghasemiesfe M, Korenstein D, Cascino T, Keyhani S. Associations Between Marijuana Use and Cardiovascular Risk Factors and Outcomes: A Systematic Review. Ann Intern Med. 2018 Feb 6;168(3):187-194. doi: 10.7326/M17-1548. Epub 2018 Jan 23. PMID: 29357394; PMCID: PMC6157910.

  9. Hancox RJ, Shin HH, Gray AR, Poulton R, Sears MR. Effects of quitting cannabis on respiratory symptoms. Eur Respir J. 2015;46:80–7. [PMID: ] doi:10.1183/09031936.00228914 [PMC free article] [PubMed] [CrossRef] [Google Scholar]

  10. 17. Tashkin DP, Simmons MS, Tseng CH. Impact of changes in regular use of marijuana and/or tobacco on chronic bronchitis. COPD. 2012;9:367–74. [PMID: ] doi:10.3109/15412555.2012.671868 [PubMed] [CrossRef] [Google Scholar]

  11. 23. Taylor DR, Poulton R, Moffitt TE, Ramankutty P, Sears MR. The respiratory effects of cannabis dependence in young adults. Addiction. 2000;95:1669–77. [PMID: ] [PubMed] [Google Scholar]

  12. Sherrill DL, Krzyzanowski M, Bloom JW, Lebowitz MD. Respiratory effects of non-tobacco cigarettes: a longitudinal study in general population. Int J Epidemiol. 1991;20:132–7. [PMID: ] [PubMed] [Google Scholar]

  13. Robert L. Page II, Larry A. Allen, Robert A. Kloner, Colin R. Carriker, Catherine Martel, Alanna A. Morris, Mariann R. Piano, Jamal S. Rana, Jorge F. Saucedo. Medical Marijuana, Recreational Cannabis, and Cardiovascular Health: A Scientific Statement From the American Heart Association.

  14. DeFilippis EM, Baja NS, Singh A, Malloy R, Givertz MM, Blankstein R, Bhatt DL, Vaduganathan M. Marijuana use in patients with cardiovascular disease.J Am Coll Cardiol. 2020; 75: 320–332. doi: 10.1016/j.jacc.2019.11.025.

  15. Rezkalla S, Kloner RA. Cardiovascular effects of marijuana.Trends Cardiovasc Med. 2019; 29:403–407. doi: 10.1016/j.tcm.2018.11.004

  16. Parekh T, Pemmasani S, Desai R. marijuana use among young adults (18-44 years of age) and risk of stroke: a Behavioral Risk Factor Surveillance System Survey Analysis.Stroke. 2020; 51:308–310. doi: 10.1161/STROKEAHA.119.027828LinkGoogle Scholar