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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.

11 Responses to this article

  1. Carol / 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.

  2. lynn / 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.

  3. Dave / 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.

  4. Avatar of Kathe
    Kathe / 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.

  5. Avatar of Julie
    Julie / January 11, 2012 at 3:16 pm

    RC, that’s not what the above article says at all. You should read it more closely.

    Bill, I’m in the same field, and I totally agree with you.

  6. Avatar of Grainne Kenny
    Grainne Kenny / January 11, 2012 at 3:05 pm

    I wonder who funded this report? How can you compare a daily tobacco user (addicted)to a recreational(2-3 month)cannabis user. The tobacco smoker would have started on 2-3 monthly until becoming addicted. As an experienced therapist I can assure you that this carcinogenic drug being highly addictive will lead the user to smoking daily. None smokes ‘recreationally’ over 20 years. Besides the study did not state that it was NOT harmful to the lungs. Less means less it does not imply NOT harmful. To-day’s cannabis is very different to that smoked in the past 20 years. Leading to the Dutch now naming it as a HARD drug. While not defending tobacco which leads to cancers, strokes and coronaries, cannabis includes all those diseases along with sometimes irreversible mental illness. Perhaps the pothead activists should put that in their pipes and smoke it.

  7. Avatar of cd
    cd / January 11, 2012 at 2:43 pm

    Actually, the study does say that “occasional and low cumulative marijuana use was not associated with adverse effects on pulmonary function.” The median use was 2-3 times a month, with 1 joint at each usage.

  8. rc / January 11, 2012 at 12:57 pm

    the article didn’t say occasional use, it says daily smokers of at least a joint a day over a 7 and 20 year period. remove it from schedule 1, legalize and tax it. But, we can’t do that, the big pharma companies couldn’t make a buck off it. you would think that a study of 20 years would come up with something to prove the governments stance of how bad it is for you. it didn’t.

  9. Avatar of bill
    bill / January 11, 2012 at 12:08 pm

    I’ve been in the substance abuse teatment field for three decades and

    1. I don’t know many individuals who only smoke marijuana 2 – 3 X’s / month.

    2. I don’t know many individuals who do not inhale as much marijuana smoke as they can and hold it for as long as they can. Something about dose selection.

  10. Avatar of jeff
    jeff / January 20, 2012 at 1:17 am

    Right on Bill! Ditto what you say. . .smoking 2-3x a months vs. daily smoking of 10-30 cigarettes. . .this isn’t apples and oranges. . .really skewed study.

  11. Avatar of Joan
    Joan / February 15, 2012 at 11:26 am

    Kathe – All of the symptoms you have described can be a result of withdrawal from marijuana and long term use of it. Try going without it for a couple months and see if there is any reduction in symptoms prior to utilizing other drugs if you are concerned. Additionally, COPD is generally a result of long term smoking, including cigarettes, marijuana, and secondhand smoke, regardless of the period in which you were exposed. Particularly, you reported 17 yrs of tobacco use and 30 of marijuana – this appears to be your source. Of course the doctors are going to suggest not smoking marijuana as it’s likely a factor in the cause of COPD and will exasperate the symptoms. I’m going to guess they have given up on attempting to convince you to stop overall…although that is a failure on their part. Please be reminded that marijuana is a depressant and may cause further lung complications via circulatory and pulmonary functions.

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