Study finds no link between marijuana use and lung cancer

May 23, 2006 |

People who smoke marijuana–even heavy, long-term marijuana users–do not appear to be at increased risk of developing lung cancer, according to a study to be presented at the American Thoracic Society International Conference on May 23rd.

Marijuana smoking also did not appear to increase the risk of head and neck cancers, such as cancer of the tongue, mouth, throat, or esophagus, the study found.

The findings were a surprise to the researchers. “We expected that we would find that a history of heavy marijuana use–more than 500-1,000 uses–would increase the risk of cancer from several years to decades after exposure to marijuana,” said the senior researcher, Donald Tashkin, M.D., Professor of Medicine at the David Geffen School of Medicine at UCLA in Los Angeles.

The study looked at 611 people in Los Angeles County who developed lung cancer, 601 who developed cancer of the head or neck regions, and 1,040 people without cancer who were matched on age, gender and neighborhood. The researchers used the University of Southern California Tumor Registry, which is notified as soon as a patient in Los Angeles County receives a diagnosis of cancer.

They limited the study to people under age 60. “If you were born prior to 1940, you were unlikely to be exposed to marijuana use during your teens and 20s–the time of peak marijuana use,” Dr. Tashkin said. People who were exposed to marijuana use in their youth are just now getting to the age when cancer typically starts to develop, he added.

Subjects were asked about lifetime use of marijuana, tobacco and alcohol, as well as other drugs, their diet, occupation, family history of cancer and socioeconomic status. The subjects’ reported use of marijuana was similar to that found in other surveys, Dr. Tashkin noted.

The heaviest smokers in the study had smoked more than 22,000 marijuana cigarettes, or joints, while moderately heavy smokers had smoked between 11,000 to 22,000 joints. Even these smokers did not have an increased risk of developing cancer. People who smoked more marijuana were not at any increased risk compared with those who smoked less marijuana or none at all.

The study found that 80% of lung cancer patients and 70% of patients with head and neck cancer had smoked tobacco, while only about half of patients with both types of cancer smoked marijuana.

There was a clear association between smoking tobacco and cancer. The study found a 20-fold increased risk of lung cancer in people who smoked two or more packs of cigarettes a day. The more tobacco a person smoked, the greater the risk of developing both lung cancer and head and neck cancers, findings that were consistent with many previous studies.

The new findings are surprising for several reasons, Dr. Tashkin said. Previous studies have shown that marijuana tar contains about 50% higher concentrations of chemicals linked to lung cancer, compared with tobacco tar, he noted. Smoking a marijuana cigarette deposits four times more tar in the lungs than smoking an equivalent amount of tobacco. “Marijuana is packed more loosely than tobacco, so there’s less filtration through the rod of the cigarette, so more particles will be inhaled,” Dr. Tashkin said. “And marijuana smokers typically smoke differently than tobacco smokers–they hold their breath about four times longer, allowing more time for extra fine particles to deposit in the lung.”

One possible explanation for the new findings, he said, is that THC, a chemical in marijuana smoke, may encourage aging cells to die earlier and therefore be less likely to undergo cancerous transformation.

The next step, Dr. Tashkin says, is to study the DNA samples of the subjects, to see whether there are some heavy marijuana users who may be at increased risk of developing cancer if they have a genetic susceptibility for cancer.

From American Thoracic Society

16 Responses to Study finds no link between marijuana use and lung cancer

  1. marcus May 13, 2012 at 4:24 pm #

    the man who wrote this reply to the page is obviously not older than 25. he has shown that using the word “good” is acceptable. he is obviously not ready to write a reply to this subject.

  2. anonymous March 21, 2012 at 11:23 am #


  3. Jay July 7, 2010 at 11:31 am #

    The fact is that marijuana like any other drug has its cons but compared to the other illegal drugs as well as legal drugs marijuana has very little downsides. Alcohol and tobacco kill hundreds of thousands a year. Never have I found a death solely related to marijuana

  4. Anonymous November 14, 2009 at 11:50 am #

    Just because someone prints something in a scientific journal it doesn’t mean that the data is good data. I haven’t seen the detailed methodology of it but from this brief abstract..

    a) Omitting patients over the age of 60 is a flaw as cancer increases in prevelance with age. So you would be missing out on a large group of people.

    b) the people conducting the study didn’t adjust for confounding factors. It could be any number of issues which increases a person’s susceptiblity of cancer. Unless you do a randomised control trial you can not prove causality

    c) 611 people in one trial is not enough evidence. 601 patients were in the head and neck region… so the other 10 were in the lungs (I guess). 10 patients are not enough to prove that marijuana use does not cause lung cancer.

    d) There is a problem with self reporting. Asking people how much they used to smoke is not always sufficient as people do lie.

    I’m not saying there is no link… i’m just saying that this isn’t enough evidence.

  5. Anonymous November 13, 2009 at 4:47 pm #

    There seems to be some confusion among previous commentators. As this article clearly states, the scientists were expecting to find that smoking weed increases one’s odds of developing lung cancer because they have long been aware of the carcinogens burning it generates.

    However, despite their expectations, no increased incidence of cancer was found even in the heaviest users.
    The researcher offered one hypothesis for why this might be, but further testing is required to answer, precisely, why the carcinogens do not lead to increased risk of cancer. However, we don’t have to know *why* it doesn’t to know that it doesn’t cause cancer.

    Generally speaking, though, smoking pot doesn’t cause cancer because carcinogens do not always cause cancer. We know that there is a link, but we do not its precise nature.
    It may interest you to know that oxygen (that stuff you inhale every few seconds) is also a carcinogen. That doesn’t mean you’re going to get cancer from breathing regular air. Likewise, just because marijuana smoke contains carcinogens does not mean you will get cancer from inhaling it.

    Already, THC has shown a variety of applications in fighting cancer. I eagerly await further studies into its interactions with cancerous cells, because it likely holds valuable clues to how we can cure Cancer once and for all.

  6. Anonymous November 13, 2009 at 4:37 pm #

    I believe you were trying to spell “article” so that would make this article BS as you so eloquently put it.

  7. Anonymous November 13, 2009 at 4:32 pm #

    y dont you just go join a cult and stop complaining
    the world is the way it is because of us not the government

  8. Anonymous November 13, 2009 at 12:38 pm #

    Don’t get me wrong, I love weed. I am in a bit of a stumble session right now as a result.

    Before getting excited, however, it would be advisable to read some medical journals relating to the effects of inhaling smoke released by burning materials that contain natural tars. (sorry bout the ramble). That would be the stuff that makes some types of weed realy sticky… When burned several types of carcinogen are released along with carbon monoxide due to the incomplete combustion. Because of this the smoke CAN AND DOES CAUSE CAUSE CANCER AND EMPHASAEMA ETC…

    Then there’s the bacci…

    But that is why God created VAPORISERS!!!

    By heating your bud to the perfect temperature the good stuff vaporises, leaving most shit in the remains. All you do is suck on the tube like a shisha…

    The very expensive but awesome “Volcano” vaporiser fills a re-useable bag for you so you can pass it round or have a large bong sized hit!!!

    So this artical is BS but there are loads of potential beneficial uses for the green. – including just fun and relaxation.

    Fuck governments who ban shit to gain votes from people who do not understand the nature of the plant or its many thousands of lovers (and haters) across the world.

    Get the money out of the black market….
    Get tax from the sales…
    Got the money for the treatment of the guarenteed increase in cannabis related illness…
    Got more time for police to catch theives and shit…

    The (otherwise) Good Doctor

  9. Anonymous November 13, 2009 at 12:29 pm #

    My son has been smoking all of his life ( pot) and has a terrible cough..he refuses to see a doctor but I already know he has COPD, because he sounds just like me and I have it. And he’s easily out of breath. No one can seriously think they can pump all that smoke into their lungs and not cause some sort of health problems???? If you think this way then join the people who think we can do the same with our air pollution and have no long term effects…

  10. Anonymous November 13, 2009 at 11:43 am #

    By the time I scrolled down to the comment box
    forgot what what the article was about

  11. Anonymous November 13, 2009 at 10:34 am #

    Let’s see.
    I’ve been smoking just about everyday, several ‘blunts’ or ‘joints’ or ‘bowls’ a day, for about 3.5-4 years. I’m relatively healthy. I also smoke cigarettes lightly.

    I do not think our world is pathetic and fucked.
    I think we could definitely use some changes, don’t get me wrong. I think Obama is a start in the right direction. I also have a feeling in my gut that by the time he’s out of office [in 8 years?] he hopefully [:3!!!!] will have made pot legal. I think it’ll deff be like alcohol and be 21, or 18 +.

    However, it’s not harmful, these studies and few others that have been done prove that. Scientists are pro-marijuana! The government, well some officials, are against it.

    The reason pot is illegal is because of a smear campaign run in the 30’s/40’s by people with money in the timber industry. Pot was such a wonderful find. It can be used as paper, as well as recreational and medicinal uses. That’s a scary thought for people who’s job is cutting down trees. Marijuana plants grow faster, easier and are more widely available for paper, smoking, and meds than trees.

    come on, world. Make the leap.
    roll a joint, toke up and smile already. :3

  12. Anonymous November 13, 2009 at 9:45 am #

    Maybe if you weren’t so gullible and believed everything you were told about a “bad drug.” Or maybe if you were someone who would actually TRY something before dogging it. Marijuana is natural ANTIdepressant. All around good for you. Makes YOU THINK, garrentee you 99% of weed smokers will tell you how pathetic and fucked our world is. Where as all you “non” smokers would claim your GOVERNMENT is actually doing good for you, when really they’ve been fucking you in the ass for years claiming you have “freedom” but your freedoms are limited, so that you don’t learn about what they’re robbing you of. Stealing candy from a baby.

  13. Anonymous November 13, 2009 at 9:07 am #

    To the previous poster: It’s your prerogative to announce your opinion, but please remember to actually read the article you’re debasing. They studied a total of 2,252 people, not 611. :)

    As for the article itself, I’m glad to see more studies like this. The more we know about the effects of marijuana, the more we can treat it properly, and, dependent on the results, maybe lighten the laws. If cigarettes cause cancer and alcohol ruins your liver, and are as of yet still legal, I’m still curious as to how marijuana is not legal when scientists are either hard pressed to find long-term damage in pot smokers or are just not interested enough to research further.

  14. Anonymous November 13, 2009 at 7:01 am #

    611 people is not a study…the fact is burning something creates carcinogens…inhaling something that is burning is INHALING CARCINOGENS…

    people need to stop rationalizing what is a horribly unhealthy and widely abused drug.

  15. Anonymous December 10, 2009 at 6:51 pm #

    Um, if you could read and comprehend correctly, you would know that there were 611 patients of lung cancer in the trial, not 10. There were also 601 people with cancer in the head or neck regions, an then 1,040 other people. So that is 2,252 people, which seems appropriate, considering that the study was for the Los Angeles area.

    Also, it wouldn’t make sense to include a group of people that were less likely to be exposed to marijuana just because they are over 60 and more likely to have cancer. That wouldn’t help the study at all, because the study was to see if marijuana use led to cancer, not to see if people over 60 who didn’t use marijuana had cancer.

  16. Fluffle September 4, 2007 at 12:43 am #

    Wow, this overwhelms me with joy!

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