Http://Smoking.Drugabuse.GovWebsite for September, 2006
http://smoking.drugabuse.gov - Nicotine is a drug!
A habit is something that people do so often that they're no longer aware they're doing it. Do you have a bad habit? Do you have a co-worker with a bad habit? Perhaps your co-worker takes a lot of smoke breaks or doesn't pay attention to where he spits tobacco. Those may seem like bad habits, but they're more than that - they're signs of addiction.
Nicotine is an addictive drug. The National Institute on Drug Abuse (NIDA) has a website that includes the effects of tobacco. http://smoking.drugabuse.gov emphasizes the addictiveness of nicotine with a fact sheet and a research report. The main website for NIDA, http://smoking.drugabuse.gov, lists many drugs but still calls tobacco "one the most heavily used addictive drugs in America."