Smokers get a very small dose for cigarettes as one cigarette contains about 10mg of nicotine of about 1-2mg is inhaled directly. Although the amount of nicotine that enters the body is particularly small, it is still enough for humans to become dependent on nicotine, thus developing a nicotine dependency, which makes it very difficult to stop smoking.
Once smokers become dependent on nicotine, they may experience strong physical and emotional withdrawal symptoms when they try cutting the habit. These symptoms usually include anxiety, headaches, lack of concentration, irritability, dizziness, disturbed sleeping patterns, feelings of anger, depression, tiredness as well as incredible cravings for more nicotine.
These withdrawal symptoms are at their highest during the first 72 hours after giving up, after which they lesson slightly. Generally, after about 6 weeks these symptoms subside, although an ex-smoker may still have the desire to smoke 6 months or even a year after they quit.
Some people have an enzyme in their body that is not as effective as other people in breaking down and metabolizing the nicotine. As a result the nicotine stays in their brain and bloodstream for an extended period of time, this means that they smoke less, as the higher levels of nicotine that is needed to give them pleasure are preserved in the body for much longer. It has been discovered by scientific studies that nicotine increases dopamine levels in a smoker's brain.