Occasional marijuana use isn't bad for the lungs, according to a UCSF study. (Chuck Grimmett: Flickr)
Occasional marijuana use isn't bad for the lungs, according to a UCSF study. (Chuck Grimmett: Flickr)

Smoking an occasional marijuana joint isn’t bad for your lungs. In fact, lighting up once in a while may increase lung function, according to researchers at University of California, San Francisco.

The UCSF study, released today, looked at the pulmonary functions of 5,000 men and women over a 20 year period. It found that those who smoked marijuana for up to seven “joint-years” had a slight increase in lung capacity. What the heck is a “joint-year”? It’s defined as an average of one joint a day for seven years, or about one a week for 49 years.

But that doesn’t mean that marijuana smokers have the lung capacity of “The Thing” in Fantasic Four. The change in lung capacity doesn’t have much of a functional impact, according lead author and UCSF professor Mark Pletcher. “The amount of lung volume that is extra in marijuana smokers at that level versus non-marijuana smokers is very small.”

Pletcher says that small difference in lung capacity may simply be because marijuana smokers are better test takers. “People who smoke marijuana tend to inhale very deeply when they smoke, so that may train them for the actual pulmonary function test — so they can inhale and exhale more quickly and more deeply.”

Pletcher says while that may be good news for medical marijuana users, smoking may still cause coughing, phlegm and even wheezing. And smoking too much marijuana may have a negative affect on the lungs. He said the data suggested that very heavy marijuana use was linked to adverse effects on pulmonary function similar to tobacco use.

“When you get above 10 joint-years of exposure, we saw that the more you smoke, the lower your pulmonary function. But we couldn’t really prove it because there weren’t a lot of heavy smokers in our sample.”

UCSF Study: Smoking Marijuana (Occasionally) Isn’t Bad For Lungs 11 January,2012Shuka Kalantari

  • It is much safer to smoke marijuana than tobacco, but if you use edible cannabis products it is even better, and it can relieve pain.
    Great e-book on medical marijuana: MARIJUANA – Guide to Buying, Growing, Harvesting, and Making Medical Marijuana Oil and Delicious Candies to Treat Pain and Ailments by Mary Bendis, Second Edition. This book has great recipes for easy marijuana oil, delicious Cannabis Chocolates, and tasty Dragon Teeth Mints. goo.gl/iYjPn goo.gl/Jfs61

  • Holzbek

    I have concerns with the presentation of this research. While it may be good news for medical marijuana users who need it to treat serious conditions, the report does not note that most research still shows a host of other possible side effects, including the possibility of physical or mental addiction that may occur in a percentage of users, the lost of mental sharpness, and the fact that marijuana is more dangerous to use while driving than alcohol. Having witnessed marijuana addiction in several individuals, I hope future reports relieving medicinal users of worry might be tempered with these reminders for the general population.

    • Shuka Kalantari

      Our post focused on the latest research findings — lung function in marijuana smokers. That said, this is a subject that is important in California and we will continue to follow it.

    • Here is a new Study proving that Marijuana is not linked with Long Term Cognitive Impairment:

      * Nearly 2,000 young Australian adults (aged 20-24) were followed for eight years. It was found that marijuana had little long-term effect on learning and memory, and any cognitive damage that did occur as a result of cannabis use was reversible.
      * Researchers categorized them as light, heavy, former or non-users of cannabis based on their answers to questions about marijuana habits.

      * Prior studies have found that drug users do accurately report their consumption levels in surveys like this as long as anonymity is guaranteed and there are no negative consequences for telling the truth.

      * Participants took tests of memory and intelligence three times over the eight year period the study. They were also asked about how their marijuana use had changed. When the results were at last tabulated, researchers found that there were large initial differences between the groups, with the current marijuana smokers performing worse on tests that required them to recall lists of words after various periods of time or remember numbers in the reverse order from the one in which they were presented.

      * However, when the investigators controlled for factors like education and gender, almost all of these differences disappeared. The lower education levels of the pot smokers — and their greater likelihood of being male — had made it look like marijuana had significantly affected their intelligence. In fact, men simply tend to do worse than women on tests of verbal intelligence, while women generally underperform on math tests. The relative weighting of the tests made the impact of pot look worse than it was.

      * Researchers then explored whether quitting cannabis would affect the one difference that remained, which was poorer performance by heavy users on a test that required immediate recall of a list of nouns. They found that heavy users who had quit by the end of the study were no longer distinguishable on this measure from those who had never used.
      The authors, who were led by Robert Tait at the Centre for Mental Health Research at Australian National University, conclude:
      “Cessation of cannabis use appears to be associated with an improvement in capacity for recall of information that has just been learned. No other measures of cognitive performance were related to cannabis after controlling for confounds.”

      The research was published in the journal Addiction.

  • 1) Tobacco is cancer causing largely because it delivers specific carcinogens such as NNK and NNAL that are not present in cannabis. Not all “tar” is created equal, and tobacco has some of the most carcinogenic types of tar known to science, whereas cannabis does not.


    2) Cannabis (marijuana) use is associated with a DECREASE in several types of cancer… potentially even providing a protective effect against tobacco and alcohol related cancer development.

    Donald Tashkin, a UCLA researcher whose work is funded by NIDA, did a case-control study comparing 1,200 patients with lung, head and neck cancers to a matched group with no cancer. Even the heaviest marijuana smokers had no increased risk of cancer, and had somewhat lower cancer risk than non-smokers (tobacco smokers had a 20-fold increased lung cancer risk). Tashkin D. Marijuana Use and Lung Cancer: Results of a Case-Control Study. American Thoracic Society International Conference. May 23, 2006.

    Researchers at the Kaiser-Permanente HMO, funded by NIDA, followed 65,000 patients for nearly a decade, comparing cancer rates among non-smokers, tobacco smokers, and marijuana smokers. Tobacco smokers had massively higher rates of lung cancer and other cancers. Marijuana smokers who didn’t also use tobacco had no increase in risk of tobacco-related cancers or of cancer risk overall. In fact their rates of lung and most other cancers were slightly lower than non-smokers, though the difference did not reach statistical significance. Sidney, S. et al. Marijuana Use and Cancer Incidence (California, United States). Cancer Causes and Control. Vol. 8. Sept. 1997, p. 722-728.


Shuka Kalantari

Shuka Kalantari is a Bay Area journalist reporting on health, food, culture and immigrant communities in California and internationally. She’s reported for Public Radio International’s The World, BBC World News Service’s Outlook, Philosophy Talk, Vice Magazine. Shuka is also a frequent contributor to KQED Public Media. You can follow her @skalantari on Twitter and Instagram.

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