It doesn't harm normal tissue. It's a natural ingredient in a lot of vegetables and has been used as a medicine for centuries by native tribes in several ways. It's anti-bacterial and was used to pack open wounds to prevent infection. Like caffeine it's also a mild stimulant and it's no more addictive than caffeine. The danger comes from the additives added to it by companies along with pesticides and herbicides. And of course from smoking it, but smoking anything is dangerous. Not because of the nicotine but because of the tar and gases that come from burning it. Smoking dried lettuce, spinach or anything else would cause the same problems.