Nicotine doesn't stick around your body for too long. It has a half-life of about 60 minutes, meaning that six hours after a cigarette, only about 0.031 mg of the 1 mg of nicotine you inhaled remains in your body.
How does your body get rid of nicotine? Here's the process:
About 80 percent of nicotine is broken down to cotinine by enzymes in your liver.
Nicotine is also metabolized in your lungs to cotinine and nicotine oxide.
Cotinine and other metabolites are excreted in your urine. Cotinine has a 24-hour half-life, so you can test whether or not someone has been smoking in the past day or two by screening his or her urine for cotinine.
The remaining nicotine is filtered from the blood by your kidneys and excreted in the urine.
Different people metabolize nicotine at different rates. Some people even have a genetic defect in the enzymes in their liver that break down nicotine, whereby the mutant enzyme is much less effective at metabolizing nicotine than the normal variant. If a person has this gene, their blood and brain nicotine levels stay higher for longer after smoking a cigarette. Normally, people keep smoking cigarettes throughout the day to maintain a steady level of nicotine in their bodies. Smokers with this gene usually end up smoking many fewer cigarettes, because they don't constantly need more nicotine.