The effects of acute exposure to these compounds are generally reversible, while chronic exposure can result in irreversible effects. Nicotine has neurotransmission-associated toxic effects. It binds to a group of cholinergic receptors called the nicotinic receptors, which are located in ganglia, in the central nervous system, and at the neuromuscular junction. The observed symptoms of nicotine are acceleration of the heart rate, elevation of blood pressure, and constriction of blood vessels within the skin. Acute exposure to high doses of nicotine causes excessive stimulation of the nicotinic receptors.
Death can result if nicotine levels are high enough that respiration muscles become paralyzed.
In humans, it is difficult to study the effects of nicotine separately from the effects of smoking, since smoking is the principle manner in which people are exposed to nicotine. Nicotine is most likely a contributor to some of the myriad maladies caused by smoking. Children whose mothers smoked while pregnant have a higher incidence of attention deficit disorder. Studies conducted on animals, in which pregnant individuals were exposed only to nicotine, demonstrated analogous behavioral defects. These studies indicate that nicotine may be the causative agent in this effect.