Nicotine is a naturally occurring chemical primarily found in plants of the nightshade family (Solanaceae), with the highest concentrations in tobacco plants (genus Nicotiana), especially Nicotiana tabacum and Nicotiana rustica
. It is also present in much smaller amounts in common food plants such as tomatoes, potatoes, eggplants (aubergines), and peppers
. Nicotine is biosynthesized in the roots of these plants through a chemical process that joins two compounds, pyridine and pyrrolidine, before being transported to the leaves
. In tobacco plants, nicotine can constitute about 0.5 to 7.5% of the leaf's dry weight, making it the plant with the highest nicotine content
. The evolutionary role of nicotine in plants is believed to be a defense mechanism against herbivorous insects, as higher nicotine concentrations help plants survive longer
. Humans have harvested nicotine primarily from tobacco leaves for centuries, initially for ritualistic and medicinal uses, and later for recreational consumption due to its stimulating effects on the brain
. In summary, nicotine comes naturally from tobacco plants, which produce it in their roots and accumulate it in their leaves, with trace amounts also found in other nightshade family plants commonly consumed as food
