Marijuana smoke does not damage lungs in the same manner as tobacco smoke, according to a study released Tuesday. But that conclusion probably will not change minds as to whether the drug should be legalized.

The study found that smoking marijuana on an occasional basis does not appear to significantly damage the lungs. Published in the Journal of the American Medical Assn., the paper supports previous research that has also failed to find a link between low or moderate exposure to marijuana smoke and lung damage. Marijuana contains many of the same chemicals as tobacco smoke.

Researchers led by Mark Pletcher at UC San Francisco studied 5,115 men and women in four U.S. cities regarding their current and lifetime exposure to tobacco smoke and marijuana smoke and their lung function. The exposure to marijuana smoke was expressed by “joint years,” with smoking 365 joints or filled pipe bowls being equal to one joint year.

The study showed that lung function declined with increased exposure to tobacco smoke. However, that same pattern was not seen with marijuana smoke. There was no evidence of lung function damage with seven joint years (or smoking one joint a day for seven years.) After 10 years, there was some decline in lung function as measured by the speed at which a person can blow out air.


“Our findings suggest that occasional use of marijuana for [medical] purposes may not be associated with adverse consequences on pulmonary function,” Pletcher said in a news release. “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.”

Understanding the pros and cons of marijuana use is of growing interest as marijuana usage rates rise and as states considered legalization of marijuana for medical or even recreational purposes. Pro-legalization advocates said the study shows marijuana can be used safely.

“To those familiar with the science of cannabis, JAMA’s [Journal of the American Medical Assn.'s] findings should come as no great surprise,” said Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws, in a blog post. He adds that marijuana can be used in ways that avoid most lung irritation.

". . .ingestion of cannabis via alternative methods such as edibles, liquid tinctures, or via vaporization — a process whereby the plant’s cannabinoids are heated to the point of vaporization but below the point of combustion -- virtually eliminates consumers’ exposure to such unwanted risk factors and has been determined to be a ‘safe and effective’ method of ingestion in clinical trial settings,” Armentano said.

However, the National Institute on Drug Abuse maintains marijuana is dangerous on many other levels, such as by impairing driving and interfering with learning and brain development when used by adolescents.


“The use of marijuana can produce adverse physical, mental, emotional, and behavioral effects,” said Dr. Nora Volkow, director of the institute, writing on the NIDA website. “It can impair short-term memory and judgment and distort perception. Because marijuana affects brain systems that are still maturing through young adulthood, its use by teens may have a negative effect on their development. And contrary to popular belief, it can be addictive.”

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