尼古丁（英语：Nicotine）是一种发现于茄科植物的强效拟副交感神经生物碱，并且是一种兴奋剂药物。尼古丁是一种烟碱型乙酰胆碱受体（一种哺乳动物和昆虫的神经突触后膜上的Na⁺/K⁺离子载体（钠钾泵））激动剂，而在nAChRα9和nAChRα10上作为受体拮抗剂。 尼古丁在茄科植物的根部上合成并蓄积在叶片上。尼古丁发现于烟草的叶子上，在黄花烟草中含量约为2-14%。

Nicotine is a potent parasympathomimetic alkaloid found in the nightshade family of plants (Solanaceae) and is a stimulant drug. Nicotine is a nicotinic acetylcholine receptor (nAChR) agonist, except at nAChRα9 and nAChRα10 where it acts as an antagonist. It is made in the roots of and accumulates in the leaves of the nightshade family of plants. Nicotine is found in the leaves of Nicotiana rustica in amounts of 2–14%, the tobacco plant Nicotiana tabacum, Duboisia hopwoodii and Asclepias syriaca.