Cigarettes are addictive
The US Surgeon General's 1988 report reached three key conclusions about dependence and tobacco use:
Nicotine use produces psychoactive effects like many other drugs. And significantly, a nictoine hit from a cigarette reaches the brain in only a few seconds. The nicotine 'hits' the brain cell receptors and stimulates the release of many different neurotransmitters - the brain's chemical messengers. The release of these messengers affect how people pay attention, think, eat, deal with stress and feel pleasure.
New smokers generally feel the unpleasant side effects of nicotine, such as headaches or dizziness. But after a while their bodies get used to it, and these effects are no longer felt. Once you have been smoking for a while, your body becomes used to a certain level of nicotine, and without it, you no longer feel quite 'right'. As the effects of the nicotine wear off, you start to feel uncomfortable, uneasy and 'needing a cigarette' - these are in fact the beginnings of withdrawal symptoms as your level of nicotine drops. So to keep up your nicotine levels, you need to continually dose yourself by smoking.
So smokers go through a continual cycle of a nicotine hit, followed by withdrawal, which prompts another hit - and this happens many times a day. They also devleop a tolerance to nicotine over time, which means that they need to smoke more to get the same effect.
Almost all smokers are addicted to nicotine. Very few do not smoke daily. We only have a limited understanding of the underlying factors that contribute to nicotine addiction, but it is likely that genetic, as well as environmental factors play a part.
It is estimated that in most people, addiction is established by the time they have smoked 100 cigarettes. Trying to quit leads to a number of physical withdrawal symptoms, such as mood and performance changes, craving, irritability, tension, difficulty concentrating, insomnia and weight gain.
PCP's Nicotine and the nervous system page
Phyllis Pugh is a nuerobiologist who has put up this comprehensive site.
Nicotine Addiction in Britain
Comprehensive publication including a section on the Physical and pharmacological effects of nicotine; Psychological effects of nicotine and smoking in man; Is nicotine a drug of addiction? and more.
NOVA Online - The search for a safe cigarette
Great site for all sorts of information about cigarettes, what's in them, how they're made, how nicotine acts etc.