Smoking a joint once a week or a bit more apparently does not harm the lungs, according to the results of a 20-year study that suggests that marijuana does not damage the body as tobacco does.
The results, from one of the largest and longest studies on the health effects of marijuana, suggest that marijuana use might cause a decline in lung function for heavy users. The authors recommended “caution and moderation when marijuana use is considered.”
The Journal of the American Medical Association released the study on Tuesday by researchers at the University of California, San Francisco, and the University of Alabama at Birmingham.
The findings echo results in some smaller studies of the past that demonstrated marijuana does not carry the same risks for lung disease as tobacco.
Dr. Donald Tashkin, a marijuana researcher and an emeritus professor of medicine at the University of California, Los Angeles, said THC, the main active ingredient in marijuana, helps fight inflammation and may counteract the effects of more irritating chemicals in the drug. Tashkin was not involved in the new study.
Study co-author Dr. Stefan Kertesz, a drug abuse researcher and preventive medicine specialist at the Alabama University, said users of marijuana tend to breathe in deeply when they inhale a joint that may strengthen lung tissue.
Data from participants in a 20-year federally funded health study in young adults that began in 1985 was analyzed by study authors; the analysis was funded by the National Institute on Drug Abuse. The study randomly enrolled 5,115 men and women aged 18 through 30 in Birmingham, Chicago, Oakland, California, and Minneapolis. Roughly equal numbers of whites and blacks took part and participants were asked about recent marijuana or cigarette use on a regular basis and had several lung function tests during the study.
Overall, about 37 percent reported at least occasional use of marijuana and most users also reported having smoked cigarettes. Seventeen percent of the participants said they did smoked cigarettes but no marijuana and those results are similar to national estimates.
Kertesz said cigarette users smoked about 9 cigarettes daily on an average, while average marijuana use was only a joint or two a few times a month on an average. The effects of tobacco and marijuana were calculated by the authors separately, both in people who used only one or the other, and in people who used both. The authors also considered other factors that could influence lung function, including air pollution in cities.
It was revealed that cigarettes harm lung function, and pot didn’t. The test scores of cigarette smokers worsened steadily during the study. On the other hand, marijuana smoking as often as one joint daily for seven years or one joint weekly for 20 years was not linked with worse scores.
National Institute on Drug Abuse