In its pure form, nicotine is a strong poison. A small dose of it, injected directly into the bloodstream, will kill a person within an hour. Because it is inhaled, it only takes seven to 10 seconds to reach the brain – twice as fast as intravenous drugs and three times faster than alcohol.
Once there, it mimics some of the actions of adrenaline. After a few puffs, the level of nicotine in the blood skyrockets, the heart beats faster and the blood pressure increases. The result is that the smoker feels more alert and may actually think faster.
In addition, nicotine may produce a calming effect by triggering the release of natural opiates called beta-endorphins. Thus, smoking produces two feelings: alertness and calmness.
Since nicotine can't be stored in the body, you must smoke more to maintain a relatively constant level in the blood. This is why you suffer withdrawal symptoms when you stop using.
Find more information about tobacco at Health Canada and get help quitting at the Smokers’ Helpline.