Moderate marijuana use doesn't have big impact on lung function

Researchers tested more than 5,000 people who reported their marijuana and tobacco use for about 20 years, regularly testing lung function to see how lung performance was affected over time.

Health

With low to moderate levels of marijuana use – about one joint a day for seven years – researchers found no significant change in lung function. People taking part in the study didn't lose air flow or volume in their lung tests. 

"In essence, marijuana doesn't seem to behave like tobacco at those levels of use," Dr. Stefan Kertesz said. 

The risk for long-term lung damage due to marijuana use increases with higher level of use, but not significantly, doctors said. In some patients, there was even an increase in lung function. 

Doctors attribute that to the way people breathe when smoking marijuana, with deep breaths in and out. That can actually improve the way people handle lung function tests like the ones researchers employed during the course of the study. 

Despite the findings, however, doctors aren't recommending people smoke marijuana. 

"The effects of marijuana change, depending on how much a person has used over their lifetime," Kertesz said. "It would be very incorrect to look at this study and say, 'Wow, if I smoke marijuana, that's going to improve my lung health.'" 

Researchers also pointed out in the most recent study that low to moderate marijuana use has previously been associated with small increases in lung function.