Asthma/AllergyCancerCOPDMarijuana (Cannabinoids)

Effects of marijuana on lung function

Some changes were reported in this study by researches at the University of Otago, in Dunedin, New Zealand.

But what does it mean for you and me?

First, the details.

  • The associations between cannabis use and lung function were recorded in 1,037 people.
  • Cannabis and tobacco use were reported at ages 18, 21, 26, and 32 years.
  • Spirometry (lung function), plethysmography (lung volume), and carbon monoxide transfer factor (measure of blood flow through the lungs) were measured at 32 years.
  • Associations between lung function and exposure to cannabis and tobacco were adjusted for exposure to the other substance.

And, the results.

  • Cannabis use was associated with increases in the following:
    • Forced vital capacity (maximum amount of air a person can expel from their lungs)
    • Total lung capacity (volume of the lungs after a maximal inspiration)
    • Functional residual capacity (air left after passive exhalation)
    • Residual volume (air left in the lungs after maximal exhalation)
    • Airway resistance (mechanical factors that limit the access of inspired air)
  • Cannabis use was not associated with…
    • Forced expiratory volume in 1 second (amount you can exhale in 1 second),
    • Forced expiratory ratio or transfer factor (a calculation that’s reduced in obstructive lung disease)
  • These findings were similar among those who did not smoke tobacco.
  • In contrast, tobacco use was associated with lower forced expiratory volume in 1 second, lower forced expiratory ratio, lower transfer factor, and higher static lung volumes, but not with airway resistance.


The bottom line?

Based on this study, cannabis appears to have different effects on lung function from those of tobacco.

And, although there are changes in physiological function, there’s “little evidence for airflow obstruction or impairment of gas transfer.”

OK, but what about the risk of lung disease or lung cancer?

Others have reported, “Long-term cannabis smoking increases the risk of lung damage, causing both asthma and chronic bronchitis.”

Regarding lung cancer, the results are mixed. Possible reasons that studies detect lung damage but not cancer in marijuana smokers, according to one review, include young age of the smokers studied, small number of people included in each study, and lack of long-term monitoring.

However, in 1 study, “Longer duration of marijuana smoking was associated with an increased risk of getting lung cancer.”

There’s more to learn about marijuana’s effects on the lungs.

3/4/10 20:24 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.