Marijuana vs. Tobacco: Evaluating A Controversial New Study

Hands offering marijuana and cigarettes
A study from the University of Ottawa suggested that smoking marijuana might be more harmful to the lungs than tobacco, causing a stir in the media. However, the study faced criticism due to its methodology, including the lack of a "marijuana-only" group and the fact that many of the marijuana smokers also smoked cigarettes. Despite these concerns, the Centers for Disease Control (CDC) and other studies have indicated that marijuana smoke may not pose the same risks to lung health as tobacco. While the conversation on the relative risks of smoked marijuana versus potential benefits is ongoing, alternative delivery methods such as water filtration pipes and medically approved vaporizing devices are being explored for safer cannabis consumption.
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Smoking marijuana might be more harmful to your lungs than tobacco, study suggests.”

This headline appeared in the Chicago Sun-Times in late 2022. It was just one of a flurry of similar, but ultimately short-lived, articles in the popular press generated by a small study released in the journal Radiology.

The study, titled “Chest CT Findings in Marijuana Smokers,” was conducted by a group of radiologists from the University of Ottawa. Using medical records, the radiologists compared CT chest scans for three groups made up of 56 marijuana smokers, 57 non-smokers, and 33 tobacco-only smokers.

Based on their evaluations, researchers concluded:

Airway inflammation and emphysema were more common in marijuana smokers than in nonsmokers and tobacco-only smokers.

This is the sentence that grabbed the headlines, but many journalists largely ignored the next part of the concluding statements, which added:

Variable inter-observer agreement and concomitant cigarette smoking among the marijuana-smoking cohort limits our ability to draw strong conclusions.

In plain speak, the scientists are telling us that there’s more to the story. A closer reading of the study reveals why:

It turns out that 50 of the 56 subjects in the “marijuana-smoking cohort” also happened to smoke cigarettes.

Backlash Against Marijuana/Lung Study

While the popular press went for the easy headlines, the medical research community wasn’t equally impressed. In short order, the Ottawa group’s study drew a number of unfavorable critiques and criticisms based on the way the data was sourced, the relatively small size of the study, the lack of a “marijuana-only” group, and the significant number of other uncounted variables.

A concise explanation of these criticisms appeared in the online publication Inverse. The author, Katie Macbride, writes:

The study authors concluded that the marijuana and tobacco group had more lung damage than to the lungs than tobacco alone did. That isn’t a terribly surprising conclusion. Inhaling smoke, be it wildfire, marijuana, or cigarette smoke, will damage your lungs. Certainly, some kinds of smoke can be more damaging than others, so it may well be that a history of inhaling two types of smoke might damage a person’s lungs more than inhaling just one kind.

She also quoted Harvard Medical School’s Dr. Peter Grinspoon, who said:

The only way they found participants for the marijuana group was screening [medical] charts for ‘marijuana’ and ‘cannabis.’ They just randomly searched the charts for the word marijuana or cannabis. They didn’t even talk to cannabis users. They didn’t quantify how much cannabis the participants were using or whether it was illegally sourced cannabis, which can have contaminants, or legally sourced.

Dr. Grinspoon also suggested that the study should be retracted. Based on his statement and similar opinions from others in the field, it seems that the University of Ottawa might turn out to be more of a “nothing burger” than a bombshell.

Is It OK To Inhale Marijuana Smoke?

Putting the disputed conclusions of this particular study aside, there are some legitimate concerns that should be investigated by anyone considering smoked marijuana as their preferred method of cannabis therapy.

The Centers for Disease Control (CDC) names cigarette smoking as the number one risk factor for developing lung cancer, and reports that it is linked to 80 to 90% of all lung cancer deaths. Studies have also shown that up to 50% of long-term tobacco smokers will eventually develop chronic obstructive pulmonary disease (COPD).

It’s fair to ask if smoked marijuana might pose similar risks. Historically, assessing the risks of long-term marijuana smoking under controlled clinical conditions has proven challenging for several reasons. In an era where marijuana use was deemed illegal, most studies were forced to rely on user-reported data or medical record searches, which typically leaves many unanswered questions as to the frequency and nature of the substance consumed, as well as a wide range of other variables that might affect outcomes.

Based on currently available information, there are indicators that smoked marijuana may not pose the same risks to lung health as tobacco. A 20-year assessment of 5,000-plus tobacco and marijuana users published in the Journal of the American Medical  Association reported that light to moderate marijuana consumption (defined as smoking the equivalent of one marijuana cigarette a day for periods of up to seven years) did not appear to have an adverse effect on pulmonary function. The study did note, however, that heavy to very heavy marijuana users (defined as smoking one or more joints daily for a period of more than 10 years) did show some degree of decline in respiratory volume and strength.

A comprehensive review published by the American Thoracic Society concluded:

Regular smoking of marijuana by itself causes visible and microscopic injury to the large airways that is consistently associated with an increased likelihood of symptoms of chronic bronchitis that subside after cessation of use.

But then went on to add that:

On the other hand, habitual use of marijuana alone does not appear to lead to significant abnormalities in lung function when assessed either cross-sectionally or longitudinally, except for possible increases in lung volumes and modest increases in airway resistance of unclear clinical significance.

Therefore, no clear link to chronic obstructive pulmonary disease has been established.

And that:

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.

In a follow-up commentary to this study, the author wrote that based on his assessment of the data:

Cannabis smoking is not equivalent to tobacco smoking in terms of respiratory risk.

Despite the presence in cannabis smoke of known carcinogens, toxic gases, and particulates, cannabis smoking does not seem to increase the risk of chronic obstructive pulmonary disease (COPD) or airway cancers.

In fact, there is even a suggestion that at low doses, cannabis smoking may be protective for both conditions.

A research paper titled, “Cannabis And Tobacco Smoke Are Not Equally Carcinogenic,” explains that:

Smoke from tobacco and cannabis contains many of the same carcinogens and tumor promoters. However, cannabis and tobacco have additional pharmacological activities, both receptor-dependent and independent, that result in different biological endpoints.

Among the points made in this paper is that nicotine and cannabis cause different reactions in the body because they are assimilated by way of different biological receptors. A more detailed explanation was given in the summary notes, where the author wrote:

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. Furthermore, THC inhibits the enzyme necessary to activate some of the carcinogens found in smoke.

More insight on the subject comes from a study published in the Journal of Cannabis Therapeutics, which states:

While there exists no epidemiological evidence that marijuana smokers face a higher risk of smoking-related cancers, studies have found that they do face a higher risk of bronchitis and respiratory infections. This risk is not thought to be due to cannabinoids, but rather to extraneous by-products of pyrolysis in the smoke.

Clearing The Smoke

The conversation on the relative risks of smoked marijuana versus potential benefits is ongoing, and perhaps the best advice for individuals engaged in cannabis therapy is to stay abreast of the latest developments through sources such as CannaMD.

Patients who have concerns over their own susceptibility to smoked cannabis might consider delivery methods that are known to provide equivalent dosages with a similar response time. The most obvious alternative is a water filtration pipe, commonly known as a bong.

Research dating back more than three decades has shown that water filtration can remove a significant portion of the carcinogenic substances found in marijuana smoke. Reporting on the subject by the MAPS organization indicates:

Marijuana smoke that has been passed through sufficient water will have less impact on the immune system than marijuana smoke that has not been water filtered.

And that:

Water filtration can be effective in removing components from marijuana smoke that are known toxicants while allowing the THC to pass through relatively intact.

More recently, the development of cannabis delivery through vaporization processes has provided patients with new options — and raised new questions. Dire warnings raised in recent years over the dangers of vaping were ultimately shown to be largely based on the use of illicit and unregulated products containing potentially dangerous additives. The additive that raised primary concerns was vitamin E acetate, which has been implicated as a cause of shortness of breath and lung inflammation.

CannaMD has reported on the risks associated with unregulated vaporization products and controversial additives, and recommends that patients only purchase medically approved vaporization devices and cannabis products. We have also shown that vaping-associated lung injury rates are significantly lower in states where the legalization of medical marijuana provides access to approved devices.

In fact, the use of medically approved vaporizing devices shows significant promise for low-risk cannabis delivery. The Cannabis Therapeutics study mentioned earlier reports:

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.

Similar findings come from a 2019 study titled, “A Qualitative Analysis of Cannabis Vaporization Among Medical Users.” Based on a multi-year analysis of medical marijuana patients in Rhode Island, the authors report:

[Our] results indicate that vaping has lower HI (hazard index) and ELCR (excess lifetime cancer risk ) than those of cannabis smoking by several orders of magnitude.

CannaMD warns patients to avoid inhaling products containing vitamin E acetate and to confirm with their dispensary that purchased products do not contain this agent. Patients are also encouraged to review all available information on the efficacy and safety of vaping and consult their doctors with any additional questions.

Updated: May 29, 2024

Article Written By:

Pierce Hoover

Pierce Hoover is a career journalist with more than three decades of experience in print, broadcast and online writing, editing and reporting, with more than 5,000 articles published in national and international print media and online. His focus on medical marijuana therapies mirrors his broader interest in science-based alternative medical practices.


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