From wikipedia: ( http://en.wikipedia.org/wiki/Nicotine )

> According to the American Heart Association, nicotine addiction has historically been one of the hardest addictions to break, while the pharmacological and behavioral characteristics that determine tobacco addiction are similar to those determining addiction to heroin and cocaine.

NHS: ( http://www.nhs.uk/chq/Pages/2278.aspx?CategoryID=53 )

> Cigarettes contain nicotine, which is highly addictive.

> Even if you want to quit smoking, you may find it difficult because you’re addicted to the effects of nicotine. Some research has suggested that nicotine can be more addictive than heroin.

"Only mildly physically addictive"...