This document provides an overview of nicotine, including its chemical properties, sources, dosage forms, absorption, distribution, toxicity, pharmacological effects, metabolism, and excretion. Key points include: nicotine is naturally found in tobacco plants and is the psychoactive compound in tobacco; it is absorbed rapidly through inhalation but more slowly through other routes; its effects are mediated through nicotinic acetylcholine receptors in the brain; the liver metabolizes most nicotine through CYP enzymes before it is excreted by the kidneys.