nicotine

also known as 1-methyl-2-(3-pyridyl)pyrolidine

Why is it in cigarettes?

To make and keep cigarette smokers addicted.
More nicotine absorbed by the smoker's body more quickly gives a bigger rush and creates brand loyalty.
Addicted smokers continue to buy cigarettes.

What does it mean?

Nicotine is a drug with physiological effects on the body
At low doses, it creates a pleasurable sensation and over time, changes the brain chemistry to be dependent on the regular delivery of nicotine in order to feel happy.
Nicotine's addiction is similar to "hard" drugs such as heroin and cocaine.
At high doses, nicotine can kill. A child who eats two cigarette butts can choke, or die from the nicotine in them.

More...

"Nicotine, an alkaloid, is an extremely powerful drug. The Royal College of Physicians has affirmed that the way in which nicotine causes addiction is similar to drugs such as heroin and cocaine.[2] Only 60mg of pure nicotine [about the weight of one drop of water] placed on a person's tongue would kill within minutes. Nicotine is contained in the moisture of the tobacco leaf: when the cigarette is lit, it evaporates, attaching itself to minute droplets in the tobacco smoke inhaled by the smoker. It is absorbed by the body very quickly, reaching the brain within 10-19 seconds. It stimulates the central nervous system, increasing the heart beat rate and blood pressure, leading to the heart needing more oxygen."[1]

Links

For more on nicotine, addiction, and how it interacts with the brain: http://www.health.usyd.edu.au/tob21c/m04_faqs.html#5

and: http://www.nida.nih.gov/ResearchReports/Nicotine/nicotine3.html#how

References

[1] online report: Action on Smoking and Health, Fact Sheets:The Constituents of Tobacco Smoke July 2000. -see: http://www.ash.org.uk/html/factsheets/html/fact12.html

[2] book, available online: Royal College of Physicians.ÊNicotine Addiction in Britain. 2000. Available online at : http://www.rcplondon.ac.uk/pubs/books/nicotine/index.htm