Chewing tobacco offers the same safe levels of toxicity dosage. Nicotine is quickly and thoroughly distributed throughout the body, rapidly penetrating the brain, crossing the placental barrier, and appearing in all the bodily fluids, including breast milk. The elimination half-life of nicotine in a chronic smoker is about two hours, necessitating frequent administration of the drug to avoid withdrawal symptoms or drug craving. In the early stages of nicotine use, there is accompanying nausea and vomiting since it stimulates both the vomiting center in the brain stem and the sensory receptors in the stomach. A rapid tolerance for this effect develops with continued use.
Nicotine use leads to a reduction in muscle tone.
As with all stimulant drugs, there is period of depression following use. This may explain the urgent need to have a smoke first thing in the morning. There was a study that showed that non-smokers who had depression when given a nicotine patch experienced relief from the depression. It was also found that the vast majority of depressed persons smoke. Therefore, cigarette smoking may be an attempt at self-medication for symptoms of depression.