Nicotine

"A poison used to kill cockroaches" -- www.smokefreedom.net

"Nicotine is the drug in tobacco that makes smoking a powerful addiction. Experts rank nicotine ahead of alcohol, cocaine and heroin with regard to the severity of dependence resulting from its use." -- www.bbc.co.uk/worldservice/sci_tech/features/health/tobaccotrial/inacigarette.htm