REVIEW Cytisine, also known as baptitoxine and sophorine, is a toxic alkaloid that occurs naturally in several plant genera, of the Faboideae subfamily of the Fabaceae family, including Laburnum, Anagyris, Thermopsis, Cytisus, Genista, Retama and Sophora. Cytisine is also present in Gymnocladus of the Caesalpinioideae subfamily. The palila (Loxioides bailleui, a bird), Uresiphita polygonalis virescens and Cydia species (moths), and possibly sheep and goats are not affected by the toxin for various reasons, and use m?mane, or parts thereof, as food. U. p. virescens caterpillars are possibly able to sequester the cytisine to give themselves protection from getting eaten; they have aposematic coloration which would warn off potential predators.
Despite its toxicity (LD50 i.v., in mice ca.2 mg/kg), cytisine has been used medically to help with smoking cessation: it is less effective but much cheaper than similar products. Its molecular structure has some similarity to that of nicotine and it has similar pharmacological effects. Cytisine, a partial agonist that binds with high affinity to the alpha(4)beta(2) nicotinic acetylcholine receptor, is a low-cost treatment that may be effective in aiding smoking cessation. Analysis of clinical data has shown that cytisine is an effective treatment for smoking cessation with efficacy comparable to that of other currently licensed treatments. Given its low cost and potential for public health benefit, expedited licensing of cytisine for smoking cessation is certainly warranted.
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