Why people would use such a crap drug anyway is the real mystery.
G'day.
Here's some information regarding tobacco from the book 'The Cosmic Serpent - DNA and the Origins of Knowledge' by Jeremy Narby, ...
pg 120
Second, there are fundamental differences between the shamanic use of tobacco and the consumption of industrial cigarettes. The botanical variety used in the Amazon contains up to eighteen times more nicotine than the plants used in Virginia-type cigarettes. Amazonian tobacco is grown without chemical fertilizers or pesticides and contains none of the ingredients added to cigarettes, such as aluminum oxide, potassium nitrate, ammonium phosphate, polyvinyl acetate, and a hundred or so others, which make up approximately 10 percent of the smokable matter. During combustion, a cigarette emits some 4,000 substances, most of which are toxic. Some of these substances are even radioactive, making cigarettes the largest single source of radiation in the daily life of an average smoker. According to one study, the average smoker absorbs the equivalent of the radiation dosages from 250 chest X-rays per year. Cigarette smoke is directly implicated in more than 25 serious illnesses, including 17 forms of cancer. In the Amazon, on the other hand, tobacco is considered a remedy. The Ashaninca word for "healer", or "shaman", is sheripiari - literally, "the person who uses tobacco". The oldest Ashaninca men that I knew were all sheripiari. They were so old that they did not know their own age, which only there deeply wrinkled skin suggested, and they were remarkably alert and healthy.
Intrigued by these disparities, I looked through data banks for comparative studies between the toxicity of the Amazonian variety (Nicotiana rustica) and the variety used by the manufacturers of cigarettes, cigars, rolling tobacco, and pipe tobacco (Nicotiana tabacum). I found nothing. The question, it seemd, had not been
pg 121
asked. I also looked for the studies on the cancer rate among shamans who use massive and regular doses of nicotine; again, nothing. So I decided to write to the main authority on the matter, Johannes Wilbert, author of the book
Tobacco and shamanism in South America, to put my questions to him. He replied: "There is certainly evidence that Western tobacco products containmany different harmful agents which are probably not present in organically grown plants. I have not heard of shamans developing cancers but that may, of course, be a function of several things like lack of Western diagnosis, natural life span of ingigenous people, magico-religious restrictions of tobacco use in tribal societies, etc."
It seems clear that nicotine does not cause cancer, given that it is active in the brain and that cigarettes do not cause cancer in the brain, but in the lungs, esophagus, stomach, pancreas, rectum, kidneys, and bladder, the organs reached by the
carcinogenic tars, which are also swallowed.
... there's more in the book and I highly recommend reading it.
A synopsis (with some direct quotes) of the chapters from the book can be read here ... www.enjoyperu.com/peru_travel_tours_info...r_the_jungle_tv.html 
