According to one of the largest and longest studies on the health effects of marijuana, smoking a joint once a week or a bit more apparently does not harm the lungs.
The 20-year study that bolsters evidence that marijuana does not the kind of damage tobacco does suggest that using marijuana that often might cause a decline in lung function, but there were not enough heavy users among the 5,000 young adults in the study to draw firm conclusions. The authors still recommended “caution and moderation when marijuana use is considered.”
The study by researchers at the University of California, San Francisco, and the University of Alabama at Birmingham was released by the Journal of the American Medical Association.
Study co-author Dr. Stefan Kertesz said marijuana users unlike cigarette smokers tend to breathe in deeply when they inhale a joint, which some researchers think might strengthen lung tissue. Kertesz said cigarette users on an average smoked about 9 cigarettes daily, while the average marijuana use was only a joint or two a few times a month.
The study randomly enrolled 5,115 men and women aged 18 through 30 in four cities: Birmingham, Chicago, Oakland, California, and Minneapolis. The study authors analyzed data from participants in a 20-year federally funded health study in young adults that began in 1985. The analysis was funded by the National Institute on Drug Abuse.