The first article there is very one sided and does not present the facts in a clear way at all. It presents assumptions which are not based on research as fact.
Marijuana: More harm than good wrote:
Smoke from burning marijuana pollutes the lungs and will deliver up to four times as much tar as tobacco cigarettes. And because users hold their toke longer before exhaling, the lungs are exposed to even higher levels of cancer-causing toxins. How’s that for an innocent little puff?
Sounds like it should cause more cancer than smoking cigarettes.
Marijuana: More harm than good wrote:
The damage from marijuana smoke is concentrated because of how the drug is used. Unlike regular cigarettes (don’t worry, we do not support their use either), the lack of filters on joints means nothing is held back from the lungs. Also, marijuana smokers typically inhale a larger amount of smoke, take it more deeply into the lungs, and then hold it for longer before exhaling. Thus, the lungs are exposed to even more toxins.
Wait a moment, where are the actual facts? Actual medical studies?
Since the article doesn't mention any I suppose I'll have to fill that bit in.
As the article later mentions there have been studies showing that cannabis is linked to the sort of DNA changes associated with cancer.
Marijuana: More harm than good wrote:
Evidence exists that marijuana contains abundant carcinogens which can cause chromosomal changes that precede cancer and outright malignancies.
The largest study of this kind was conducted by Dr Marinel Ammenheuser of the University of Texas in 1998. This study is based purely on pregnant women, yet it is often held up as an example, despite the fact that there are many more recent and more valid case studies that show the opposite to be true.
A great example of this is the
2006 study, the largest of its kind ever, by Donald Tashkin of the University of California, this study concluded there was no link between cannabis use and cancer, in fact that it provided a mild protective effect.