What Is Nicotine?
Nicotine is a powerful alkaloid found in the nightshade (the same family as *deadly* nightshade) family of plants. A powerful neurotoxin, nicotine is used in many commercial pesticides because of the devastating effect it has on insects - killing them almost instantly.
Stimulant And Depressant
Nicotine itself acts as both a stimulant and a depressant depending on the dosage and the circumstances of absorption. Basically smoking a cigarette quickly can product a depressant effect (cigarettes calm me down) whilst smoking a cigarette slowly can produce a stimulating effect (I can focus better after having a relaxing smoke).
How Much Nicotine?
The amount of nicotine contained in 3 - 4 average cigarettes is quite capable of killing you stone
dead - instantly. 40 - 60mg of nicotine is all it takes to fatally poison a heathly adult human. Fortunately the dosage of nicotine in each cigarette is diluted dramatically by the smoking and inhaling process. The end result is that milder form of the toxin produces the desired result for the smoker.
Nicotine withdrawal can be an unpleasant process lasting anywhere from several days to several weeks. Nicotine withdrawl symptoms include headaches, nausea, irritability, loss of concentration, anxiety and insomnia. The withdrawal symptoms suffered by nicotine addicts have been compared to that of heroin addicts but this is mostly speculation especially when some nicotine addicts can quit the drug "cold turkey" with no ill effects.