Another Health Harm from Marijuana

“In a new analysis of medical records, cannabis smokers had higher rates of a certain type of emphysema than tobacco smokers.” It's another attention-grabbing headline that fails to tell the whole story. Let’s skip the public relations version and consider the study's findings.

The Study

Researchers identified chest CT scans of 56 individuals that stated they had smoked marijuana between 2005 and 2020 and then matched them with CT scans of non-smokers (being staged for sarcoma) and solely tobacco smokers (being screened for being at high risk for lung cancer). Because the smokers were all over 50 (with a mean of 40 pack-years of smoking), the non-smokers and marijuana smokers were similarly chosen – this was a “case-controlled” study.

The chest CT scans were evaluated using standardized criteria to identify.

  • Emphysema – where the walls of our airways break down, creating larger and less functional “air sacs,” resulting in trapping of air within the lung and poorer air exchange.
  • Thickening of airways – oxygen can only be transferred from the air to our circulation over short distances; thickening of the airways due to inflammation or mucus build-up reduces our ability to oxygenate fully.
  • Incidental findings – the presence of gynecomastia in males and calcifications of the coronary arteries linked with enhanced coronary artery disease.

This raises the first problem with the study but not the last. CT scans accurately depict how the lungs look, not how they function. We would need arterial blood gases and pulmonary function studies to assess the physiological impact of emphysema and thickened airways. So the results while identifying the presence of these abnormalities do not quantify their severity.

The second problem is that both the marijuana smokers and non-smokers were younger than the smokers, so while the participant pool was relatively small, to begin with, 60 participants in each “treatment” arm, when matched by age and gender, the number of marijuana and non-smokers were reduced in half. This makes the finding less certain.

The third and fatal problem is that 50 of the 56 marijuana smokers had smoked tobacco for an average of 25 pack-years, so separating the effects of marijuana from that of tobacco is a fool’s errand. But, for a moment, let us see if there is some nugget of knowledge amongst the fool’s gold of this study.

The table shows the incidence of abnormal CT findings when matched for age and gender. Don’t be fooled by that caption saying Marijuana smokers; we all know it should be marijuana and tobacco smokers. If we look at the fifth column, the p-values for marijuana vs. non-smoking, it is clear that not smoking is far better for your lungs and health than smoking pot and tobacco. No surprise there. The last column compares those who smoke only tobacco and those who smoke both, and here we find some valuable data. Smoking pot increases the damage done by those who simultaneously smoke tobacco. We do not know why this might be.

People smoke marijuana to get high, and as a result, their pattern of inhalation differs from that of a tobacco smoker – inhalation is deeper, and the pause before exhalation is longer. That would certainly increase the “dwell time” of the hot gaseous chemicals of marijuana in your lungs; no surprise, it is that pattern of inhalation that helps determine the dose and subsequent high. There is no way to quantify that dwell time. For tobacco smokers, exposure is quantified as pack years; there is no similar measure for marijuana. This further confounds the findings. Now the researchers did try to quantify the amount of marijuana smoked. Still, it required assumptions that made the quantification useless. One must question the veracity of all the participants only because marijuana was not legalized in Canada until 2018. How many people will self-report that they are breaking the law, even to their physician?

The study is deeply flawed and deserves very little of the attention it received in the media. Here is the bottom line. It harms your health to inhale hot combustion products, tobacco, or marijuana. If you are not sure of this, ask a firefighter.  

Source: Chest CT Findings in Marijuana Smokers Radiology DOI: 10.11