Score another point for medical marijuana advocates: a new study shows that smoking pot is much less harmful to users' lungs than smoking tobacco.

When researchers studied 20 years of data from more than 5,000 adults, they predictably found significant lung damage in the tobacco smokers: the more they smoked, the worse their air flow rate and lung volume became. But those who smoked up to one joint a day aced a lung function test: air flow rate actually slightly increased in the marijuana users, up to a certain level.

“We found exactly what we thought we would find in relation to tobacco exposure: a consistent loss of lung function with increasing exposure,” said the paper’s lead author, Mark Pletcher, MD, MPH, associate professor in the Division of Clinical Epidemiology at University of California, San Francisco. “We were, however, surprised that we found such a different pattern of association with marijuana exposure.”

The NIH-funded study, published in the Journal of American Medical Association, measured air flow rate (how fast you can blow out air) and lung volume (how much air you can hold) in 18- to 30-year-old adults from Oakland, Chicago, Minneapolis and Birmingham.

Researchers caution that the findings don't point to the health benefits of heavy marijuana use.

“Our findings suggest that occasional use of marijuana for these or other purposes may not be associated with adverse consequences on pulmonary function,” Pletcher said. “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.”

Source: news.discovery.com - Author: Sheila Eldred - (Wed Jan 11, 2012 12:05 PM ET)