Although cannabis smoke contains known carcinogens, there have not been any cases of cancer fatalities caused by smoking cannabis.

Kaiser Permanente is a large insurance corporation that has been following the health outcomes thousands of pot smokers for well over a decade. To their surprise, long term cannabis use is not associated with early mortality as is the case with long term cigarette smokers.

Researchers at John Hopkins Medical School also failed to detect any association between cannabis and head, neck and lung cancer.

Unfortunately, any research that concludes cannabis is not a serious threat to health does not get serious covereage in the media.

Kaiser Permanente Study:
http://www.pbs.org/wgbh/pages/frontline/shows/dope/body/mortality.html
"aside from the almost self-evident proposition that smoking anything is probably bad for the lungs, the quarter century since large numbers of Americans began to use marijuana has produced remarkably little laboratory or epidemiological evidence of serious health damage done by the drug."
- Harvard policy analyst Mark Kleiman

John Hopkins Medical School study:
http://my.webmd.com/content/article/1728.57309
"Marijuana, unlike tobacco and alcohol, does not appear to cause head, neck, or lung cancer, says a researcher from Johns Hopkins Medical School in Baltimore."

Review of Research Concerning Lung Disease and Cannabis:
http://www.pdxnorml.org/Exposing_04_1095.html
"There are no epidemiological or aggregate clinical data suggesting that marijuana-only smokers develop lung cancer."

Is cannabis use a risk to health? A look at the evidence
http://www.ccguide.org.uk/safety.html
"At present it is estimated that marijuana's LD-50 is around 1:20,000 or 1:40,000. In layman terms this means that in order to induce death a marijuana smoker would have to consume 20,000 to 40,000 times as much marijuana as is contained in one marijuana cigarette. NIDA-supplied marijuana cigarettes weigh approximately .9 grams. A smoker would theoretically have to consume nearly 1,500 pounds of marijuana within about fifteen minutes to induce a lethal response." - DEA Administrative Law Judge Francis L. Young

Pot is not only safe, it also has protective properties... its possible to use pot in a harmful way but the risks are very small compared to alcohol or tobacco use... pot is as safe to use as caffeine which means it can be part of an active healthy lifestyle or a couch potato lifestyle with very little effect on long term outcomes compared to non-users.

- Response submitted by Bob Martin