(S)-nicotine is a 3-(1-methylpyrrolidin-2-yl)pyridine in which the chiral centre has S-configuration. The naturally occurring and most active enantiomer of nicotine, isolated from Nicotiana tabacum. It has a role as a phytogenic insecticide, a teratogenic agent, a neurotoxin, an anxiolytic drug, a nicotinic acetylcholine receptor agonist, a biomarker, an immunomodulator, a mitogen, a peripheral nervous system drug, a psychotropic drug, a plant metabolite and a xenobiotic. It is a conjugate base of a (S)-nicotinium(1+). It is an enantiomer of a (R)-nicotine.