By Maria Cendejas

Sunday Jan 15, 2012 (foodconsumer.org) -- A 20-year study shows smoking a joint once a week may not harm the lungs like smoking cigarettes, Fox News reports.

The study by researchers at the University of California at San Francisco, and the university of Alabama at Birmingham was released Tuesday by the Journal of the American Medical Association.

The results, from one of the largest and longest studies on the health effects of marijuana, are hazier for heavy users or those who smoke two or more joints daily for several years. The data suggest that using marijuana that often might cause a decline in lung function, but there weren't enough heavy users among the 5,000 young adults in the study to draw a firm conclusion.

Marijuana smoke has a lot of the same toxins as cigarette smoke. People who use pot smoke fewer joints than tobacco users who smoke cigarettes.

"I think a lot more work will need to be done to make any blanket statements about safety. These are only two measures of pulmonary function and don't really paint the entire picture of the potential effects of marijuana on the lungs,“ said Dr. Jeanette Tetrault, a substance abuse researcher at the Yale School of Medicine in New Haven, who didn’t have anything to do with the new research.

The study authors analyzed data from participants in a 20-year federally funded health study in young adults that began in 1985. Their analysis was funded by the National Institute on Drug Abuse and the National Heart, Lung, and Blood Institute.

The study randomly enrolled 5,115 men and women aged 18-30 in 4 cities: Birmingham, Chicago, Oakland, and Minneapolis. Equal numbers of blacks and whites took part, but no other minorities. Participants were periodically asked about recent marijuana or cigarette use and had several lung function tests during the study.

About 37% reported at least occasional marijuana use, and most users also reported having smoked cigarettes and 17% of participants said they'd smoked cigarettes but not marijuana. Those results are similar to national estimates.

Cigarette users smoked about 9 cigarettes daily, while the average marijuana smokers use was 1-2 joints a few times a month Kertesz said.

The authors calculated the effects of tobacco and marijuana separately, both in people who used only one or the other, and in people who used both. They also considered other factors that could influence lung function, including air pollution in cities studied.

The analyses showed pot didn't appear to harm lung function, but cigarettes did. Cigarette smokers' test scores worsened steadily during the study. Smoking marijuana as often as 1 joint daily for 7 years, or one joint weekly for 20 years was not linked with worse scores.

Like cigarette smokers, marijuana users can develop throat irritation and coughs, but the study didn't focus on that, and it also didn't examine lung cancer. But other studies haven't found any positive link between marijuana use and cancer.

Medical marijuana is allowed in at least 16 states while the federal government bans the drug.  Patients with terminal diseases such as AIDS and cancer who used marijuana reported good experience using the drug. They say marijuana help pain management better than painkillers.