David. Nicotine itself is the addictive agent but it is the 400 other chemicals in tobacco particularly when it is cured or burned that are the carcinogens. That is why accepted harm reduction strategies for tobacco users use nicotine replacement therapy (NRT). They are essentially nicotine in another form, nasal sprays, inhalers, gum, patches etc. Some of these are Rx, some are OTC. But the bottom line is just like with heroin addicts, you need to give them something that satisfies the brain's addiction (without introducing additional collateral harm) while you wean the body off the addiction slowly with gradually reduced levels of the addictive nicotine itself. Those NRT's are still nicotine containing substances. But as a cause of cancer it isn't a big player. It is linked to high blood pressure and other dangerous things, but to a significantly lower level than the real danger of spit or smoked tobacco which cause the cancers that nicotine does not.
This page of the web site
http://www.oralcancerfoundation.org/tobacco/types_of_tobacco.htmtalks a bit about NRT. We are just now rewriting all this as much is changing. I would also suggest people read how the tobacco companies (below the radar and unnoticed by most adults) are still marketing their addiction to our youth on this really good blog with lots of link in it.
http://www.oral-cancer.info/?cat=20