Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Nicotine is an alkaloid found in the nightshade family of plants, such as tobacco. In low doses, the substance acts as a stimulant in mammals, while high amounts (30–60 mg) can be fatal. This stimulant effect is the main factor responsible for the dependence-forming properties of tobacco smoking. Nicotine addiction has historically been one of the hardest addictions to break, while the pharmacological and behavioral characteristics that determine tobacco addiction are similar to those determining addiction to heroin and cocaine. Learn more about the effects of nicotine on health and the diseases caused by smoking in this book.