The toxic alkaloid found in yellow jessamine and related Gelsemium plants is gelsemine.
Gelsemine is an indole alkaloid produced by flowering plants in the genus Gelsemium. Gelsemium sempervirens, native to the southeastern United States and known as yellow or Carolina jessamine, is its principal American source. The plant’s leaves, sap, nectar, and other tissues can contain gelsemine alongside related alkaloids.
Its toxicity is linked to activity at glycine receptors, inhibitory chloride channels in the nervous system. Excessive activation can relax muscles, impair involuntary control, cause paralysis, and potentially lead to death. This mechanism is why gelsemine poisoning may resemble other neurological poisonings, although it is chemically distinct from strychnine.
A common mix-up is treating “yellow jessamine” as merely a fragrant ornamental vine. The flowers have also caused accidental poisonings when their nectar was mistaken for honeysuckle. Gelsemium extracts appeared in nineteenth-century medicinal practice and later in crime fiction, but the plant should be regarded as poisonous rather than medicinally safe.