Nicotine occurs naturally in tobacco and at significantly lower levels in some other plant varieties.
Nicotine used in pharmaceutical products (nicotine replacement therapies; NRTs) as well as in e-cigarettes is usually extracted from tobacco. It is possible to produce synthetic nicotine, but the process is costly.
When tobacco smoke is inhaled, nicotine is absorbed through the lungs into the bloodstream, and begins to reach the brain within about 10 seconds. There, nicotine binds to special receptor molecules, mimicking the actions of a naturally occurring brain chemical, acetylcholine. In turn, some of these nicotine receptors activate areas of the brain that are involved in producing feelings of pleasure and reward, which may explain the subjective pleasurable effects associated with smoking, but also relates to the desire for nicotine and potential for addiction. Other pathways stimulated by nicotine may contribute to its attention-enhancing and calming effects.
Through other routes, such as absorption through the skin when using a nicotine patch, or through the mouth and stomach when chewing nicotine gum, the nicotine is absorbed more slowly and takes longer to reach the brain.
Nicotine also affects other parts of the body such as the heart and blood vessels.
Nicotine is addictive and not risk free. Minors, pregnant or breastfeeding women, and people with heart disease, severe high blood pressure or diabetes should not use tobacco or nicotine containing products.