once nicotine is inhaled, it is quickly absorbed into the system due to the high blood flow in the lungs. It only takes around ten seconds to reach the brain. Nicotine is metabolized in the liver and further breakdown occurs in the lungs and the kidneys.
The main metabolites produced are nicotine N-oxide and cotinine (major indicator of nicotine presence). Generally, it takes about 72 hours from the last use for other nicotine by-products to leave the system. Yet cotinine remains in the system for as long as four days. Cotinine can also remain for several months, depending on how much tobacco was smoked and the length of time the user has smoked.
