Nicotine is a poisonous alkaloid derived from the tobacco plant and used in medicine and as an insecticide. Nicotine is toxic to humans if enough is ingested at once, and many children are seen in emergency rooms every year after eating cigarettes or cigarette butts. Ironically, the dizziness and nausea that hit people after smoking their first cigarette is actually a very mild case of nicotine poisoning. Nicotine is toxic to our pets, too. The most common source of nicotine is tobacco products like cigarettes, cigarette butts and even nicotine gum and patches.
For more information, please read Nicotine Toxicity