There are plenty of pack-a-day tobacco smokers - far fewer 4-joint-a-day pot smokers.
But note the absence of emphysema and lung cancer from this list.
Lung cancer Wrong.
There are 33 cancer-causing chemicals contained in marijuana.
And yet YOUR PAGE does NOT say that pot causes lung cancer - because there's no direct evidence for it. In sufficient quantities, almost everything is a "cancer-causing chemical" - because in lab-rat giga-doses it kills off cells so fast that the body goes into hyper-cell-growth mode.
Cancer? Don't be ridiculous.
>>BTW, they probably made the same claims about cigs and tobacco.<<
Also, since tobacco and pot are plants, they probably possess the same materials when burned — carbon/tar, etc. So COMMON SENSE would dictate that smoking a joint is much like smoking unfiltered cigarettes.
So just like cigs, if you inhale the carcinogens, you increase your chances of getting cancer. Unless you claim that there is no increased risk of getting cancer if you smoke marijuana. Or the risk is less than smoking filtered cigs.