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Marijuana Smoking Not Linked to Chronic Breathing Problems

20-Year-Long Study Finds No Decline in Lung Function for Occasional Pot Smokers
By
WebMD Health News
Reviewed by Laura J. Martin, MD

Jan. 10, 2012 -- Woodstock generation, breathe easy. One of the largest and longest studies ever to look at the effect of marijuana smoking on lung health finds that pot smoking doesn’t appear to cause chronic breathing trouble.

The study has followed more than 5,000 young adults in four cities for more than two decades. More than half of the people in the study reported smoking tobacco, marijuana, or both.

Over time, researchers repeatedly checked two measures of lung function: One was a test that measured the amount of air forcefully exhaled in a single second. The second test measured the total amount of air exhaled after taking the deepest possible breath.

Those tests help doctors diagnose chronic, irreversible breathing problems like chronic obstructive pulmonary disease (COPD).

Cigarette smoking is a leading cause of COPD. And marijuana smoke contains many of the same chemicals as tobacco smoke.

As more states legalize marijuana -- 16 states and the District of Columbia now allow its medical use -- experts have worried that the kinds of lung damage caused by cigarettes could also be brought on by pot smoking.

Indeed, cigarette smokers in the study saw their lung function drop significantly over 20 years.

But that didn’t happen to people who only smoked marijuana.

In fact, the study found that the lung function of most marijuana smokers actually improved slightly over time.

'These Are Not the Cheech and Chongs of the World'

A healthy adult man can blow out about a gallon of air in one second, says researcher Stefan Kertesz, MD, an assistant professor of medicine at the University of Alabama at Birmingham.

Pot smokers, on average, were able to blow out that gallon of air plus about 50 milliliters.

“That’s roughly one-sixth of a size of a can of soda,” Kertesz says. “It’s not anything anybody would notice.”

The results do have to be put into the proper context, though.

Most marijuana users in the study were light smokers. “These are not the Cheech and Chongs of the world,” Kertesz says.

The average number of times a person using marijuana in the study said they lit up was two to three times per month.

But even in regular users, researchers say they still saw no evidence of breathing problems.

In fact, researchers estimated that lung capacity would stay slightly elevated even if a person had smoked as much as a joint a day for seven years, or two to three joints a day for three years.

The study is published in the Journal of the American Medical Association.

Marijuana Smoking May Stretch the Lungs

But researchers are quick to say that the small improvement seen in this study may have more to do with the way people smoke marijuana -- by taking and holding deep breaths -- than it does with any actual benefit of the drug.

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