Tobacco have nicotine which is a potent poison and highly addictive. It also may contain radioactive elements from the fertilizers that are used on the plant. It is believed by some that the radioactive elements within the fertilizer may be one reason tobacco have a high association beside lung cancer.
Marijuana contains THC which has anti-tumor properties. The most recent research by Dr. Donald Tashkin of UCLA (the ascendant expert on the subject) found that marijuana smokers actually own a LOWER incidence of lung cancer than average. This may be due to the anti-tumor properties of marijuana. You can find newspaper articles chitchat about this research by penetrating http://www.mapinc.org
As for the fertilizers used on marijuana, those will vary according to who is growing it but I own met a large number of growers and every one of them expressed great diligence about choosing the correct (and safe) fertilizers for their product. They put slightly a bit of work into each plant so they tend to examine these things very obligingly. (This would not apply to ordinary Mexican weed.)
Tobacco also cause emphysema, while marijuana does not.
I'm sorry, but in every case of a public issue like this there will ALWAYS be scientists on either side who claim one extreme or the other. Unfortunately, you can't just pick the guy who's on your side and only spout forth his views. It's better to look at clearly unbiased studies, if ur *actually* looking for the truth. Unfortunately tho, as is so often the case, the truth is more than often somewhere in the midle, and not nearly as super exiting as everyone thinks.
So in this case, let me just pause you there and explain that i too, could find studies and articles about how even one joint can give you mental illnesses. As with studies that say that smoking pot actually lowers your chance of lung cancer than those who dont smoke at all and exercise well, etc etc....It just sounds a little...influenced, doesn't it? You gotta face the facts here man.
If weed smoke was anti-tumour, would they not be isolating the exact agent that's lowering the instances of lung cancer, and use it as a cancer vaccine/treatment/cure? Because it surely would be such an amazing find that scientists all over the world would jump on it and, it would be discussed in unbiased, respected scientific forums and much, much more testing would be done.
Unfortunately tho it seems that it's probably just a flawed study that i've actually seen touted on other forums too. And often, when a study is flawed and has results like this, interpretations of it are twisted to end up saying outrageous things to support the people who truly have a point to make.
So basically either tashkin is a pro marijuana campaigner who has let his own motives influence what should have been an unbiased study, or he did a study that had unforseen influencing factors and now pro-weed campaigners are jumping on it and saying that weed is the cure for cancer. (anti-tumour and less cancer implies anti malignant tumour, which implies anti-cancer.)
*edit: i've done some quick research using my uni sources (enables me to access online peer reviewed articles etc) and surprisingly, i havent found a seemingly neutral study on weed yet. there arent even many to begin with. and then i realised that it makes a lot of sense; research studies are funded by research grants, research grants are supplied by governments, governments have political agendas when it comes to drugs. Every single bit of pro-weed study that wud be available to the public (eg via a quick google search) always quotes tashkin for some or all of their material. Ideally, i wud be multilingual and would have access to european studies on the matter - as many european countries seem to be more neutral (and thus properly scientific; science should never be political) on the topics of drugs. Nearly every successful opiate substitution program has originated in europe, because in america, giving drugs to drug addicts would be crucified in the media before it ever gained any credebility - and then it wud become apolitical argument and much less of a medical one. i suspect the same has happened here, but i dont have time to go trawling through european medical studies, so just take it from me that weed (nearly certainly) isnt good for you; nor does it cure cancer.
(i say nearly certainly because i cant get all high and mighty about being neutral and open without acknowledging that all i have learned may be wrong, and anybody else may be right. However...i doubt it.)
anyway sorry to rain on your parade but i just wanted to clear that up. altho on the same note i have never heard from a reputable medical source that one joint has the tar of an entire pack of cigarettes either...All i know for sure is that weed smoke is worse because it is smoked unfiltered and often smoked closer to the roach, which means hotter and harsher air is entering your lungs. saying that one joint would have the tar from a PACK of cigarettes seems to me like the perfect example of the extreme other side of the weed debate.
anyway just trying to shed some truth on all this, as i've said it;s one of the few areas where i actually know what im talking about