i dont have the links to the actual studies anymore, but here's a few that have some factual info
"Lung Cleaner &. Expectorant Cannabis is the best natural expectorant to clear the human lungs of smog, dust and the phlegm associated with tobacco use. Marijuana smoke effectively dilates the airways of the lungs, the bronchi, opening them to allow more oxygen into the lungs. It is also the best natural dilator of the tiny airways of the lungs, the bronchial tubes - making cannabis the best overall bronchial dilator for 80% of the population. The remaining 20% sometimes show minor negative reactions). (UCLA Tashkin Studies, 1969-83; US Costa Rican Studies, 1980-82; Jamaican Studies 1968-74.) Statistical evidence - showing up consistently as anomalies in matched populations - indicates that people who smoke tobacco cigarettes are usually better off and will live longer if they smoke cannabis moderately, too. (Jamaican and Costa Rican Studies). Millions of Americans have given up or avoided smoking tobacco products in favour of cannabis, which is not good news to the powerful tobacco lobby - Senator Jesse Helms and his cohorts. A turn of the century grandfather clause in US tobacco law allows 400 to 6,000 additional chemicals to be added. Additions since then to the average tobacco cigarette are unknown, and the public has no right to know. Many joggers and marathon runners feel cannabis use cleans their lungs, allowing better endurance. The evidence indicates cannabis use will probably increase these outlaw American marijuana-users' lives by about one or two years - but they can lose their rights, property, children, state licences, etc. for using that safest of substances: cannabis."
http://www.parklandtrading.com/users...ia/medical.php
http://www.marijuana.com/420/archive...p/t-29209.html
http://rubens.anu.edu.au/student.pro...mp/meddoc.html
or check a few of these
http://www.google.com/search?hl=en&l...nt&btnG=Search