Occasional Marijuana Smoking Not as Harmful to Lungs as Cigarettes, Study Suggests

Low to moderate use of marijuana is less harmful to the lungs than tobacco exposure, according to a new study published in the Journal of the American Medical Association. The study found that the more tobacco a person smokes, the more adversely it affects lung function. This was not true with marijuana, the researchers found.

The study included more than 5,000 adults, and followed them for more than 20 years. The researchers found people who smoked marijuana two to three times per month did not show the same reduced lung function seen in cigarette smokers, CNN reports.

“An important factor that helps explain the difference in effects from these two substances is the amount of each that is typically smoked,” researcher Mark Pletcher, MD, MPH, of the University of California, San Francisco, said in a news release. “Tobacco users typically smoke ten to 20 cigarettes/day, and some smoke much more than that. Marijuana users, on average, smoke only two to three times a month, so the typical exposure to marijuana is much lower than for tobacco.”

The researchers noted the findings suggested that very heavy marijuana use might impair lung function, but it was difficult to determine because there were so few such smokers in the study.

Marijuana smoke contains many of the same components as cigarette smoke, the article notes.

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    January 13, 2012 at 5:26 PM

    Bronchial Secretory IgA Deficiency Correlates With Airway Inflammation and Progression of COPD. VV Polosukhin et al. Am J Respir Crit Care Med 2011 Aug 1;184(3):317-327. Lifetime non-smokers and former smokers, number not given. “Areas of bronchial mucosa covered by normal pseudo-stratified ciliated epithelium were characterized by pIgR expression with SIgA present on the mucosal surface. In contrast, areas of bronchial epithelial remodeling had reduced pIgR expression, localized SIgA deficiency, and increased CD4(+) and CD8(+) lymphocyte infiltration. In small airways (< 2 mm), these changes were associated with presence of herpesvirus antigens, airway wall remodeling, and airflow limitation in patients with COPD."

    Other studies have implicated CMV, a herpesvirus, in COPD, including via CD4+CD28null T cells, which are specific for CMV. And tobacco smokers are more likely to have been exposed to CMV for socioeconomic reasons, while marijuana smokers include a larger proportion of the more privileged.

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    January 13, 2012 at 2:34 PM

    Many marijuana users like Kathe also smoke cigarettes which makes it difficult to determine what damage is caused by marijuana and what by tobacco. Kathe attributes damage solely to cigarettes, but how does she know? 2-3 joints a month should be compared to 2-3 cigarettes a month. Obviously those who use less of either have less risk, but some marijuana and medical marijuana users (including the addicted who get cards) use marijuana virtually all the time with several joints per day. Why would you need medical marijuana to use only 2-3 times a month? If the researcher wants to suggest that the study supports moderation and caution, he should have compared the lung function of occasional to heavy users of marijuana, and the study did not have enough heavy users to do that. The headline is certainly misleading and will give the green light to numerous marijuana abusers that marijuana does not cause any lung damage which the study does not prove at all.

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    January 13, 2012 at 10:16 AM

    It is important to read this study carefully. The only measure of “lung function” was lung capacity. The study did not track risk of lung cancer or other lung diseases. Study author Mark Pletcher seems to indicate in his comments that a motivation for the study was to evaluate risk for typical medical marijuana smokers. What the study says is that with occasional use (a joint a day) there is no change or even a change for the better in lung capacity. This may be because of the way that marijuana is smoked: inhaling deeply which may exercise the lung muscles. But Pletcher goes on to say: “On the other hand, our findings do suggest an accelerated decline in pulmonary function with heavier use – either very frequent use or frequent use over many years – and a resulting need for caution and moderation when marijuana use is considered.” I hope that marijuana advocates do not use this very limited study to allege that marijuana is harmless to the lungs. On the other hand, this is one positive indication that marijuana, which is medically useful for some conditions (glaucoma, disease induced anorexia, chronic pain) may not cause lung problems as an adverse consequence. However, the study does not address other commonly acknowledged adverse consequences, such as memory problems, increased risk of anxiety and mood disorders and impairment in motor and cognitive function that may interfere with driving and other complex activities. Also there still needs to be much more research on cancer risk, cardiovascular risk and other health issues that have not yet been explored. All of these issues would have had to be explored if marijuana had been approved as a medication by the usual FDA process. But this process was bypassed by approving it through referendum. So we are only beginning to determine how safe and effective it is as medication.

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    January 13, 2012 at 10:04 AM

    I have been a marijuana smoke for 30 years. I smoke regularly, and I use it for headaches, nausea, and anxiety. I have quit several times, but then the doctors put me on pills for those things. I find it hard to believe that smoking a little pot here and there could cause nearly the damage and side effects of meds. In fact, i was recently diagnosed with copd and emphysema and both my family doctor and my pulmonary doctor have suggested i make marijuana “tea” instead. I smoked cigarettes for 17 years and quit in 2007. My diagnoses was because of smoking and second hand smoke as a kid, NOT because i smoke pot. I highly believe in the medicinal qualities of the drug.

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