Cytisine, also known as baptitoxine and sophorine, is an alkaloid that occurs naturally in several plant genera, such as Laburnum and Cytisus of the family Fabaceae. It has been used medically to help with smoking cessation: one recent trial has shown cytisine to be more effective at 1 month than nicotine replacement therapy, but results by months 2 and 6 showed no difference between treatments. It is much cheaper than similar products. Its molecular structure has some similarity to that of nicotine and it has similar pharmacological effects. Like varenicline, cytisine is a partial agonist of nicotinic acetylcholine receptors (nAChRs). Cytisine has a short half-life of 4.8 hours, and is rapidly eliminated from the body. Cytisine remains relatively unknown outside Eastern Europe despite calls for licensing worldwide because of its proven benefits, low cost as compared with other cessation medications (cytisine, $20 to $30 for 25 days; nicotine-replacement therapy, $112 to $685 for 8 to 10 weeks; varenicline, $474 to $501 for 12 weeks).
As a pharmaceutical preparation, cytisine is available for the treatment of tobacco smoking. Phase III clinical trials using Tabex have shown similar efficacy to varenicline but at a fraction of the cost. Varenicline, approved in 2006 as a smoking cessation drug, has some structural and pharmacological similarities to cytisine.
Cytisine is an acetylcholine agonist, and has strong binding affinity for the nicotinic acetylcholine receptor. It is extracted from the seeds of Cytisus laborinum L. (Golden Rain acacia) and has been available in former socialist economy (FSE) countries for more than 40 years as an aid to smoking cessation under the brand name Tabex produced by the Bulgarian pharmaceutical company Sopharma AD. It was first marketed in Bulgaria in 1964 and then became widely available in FSE countries..
In 2011, a randomized controlled trial with 740 patients found cytisine improved 12-month abstinence from nicotine from 2.4% with placebo to 8.4% with cytisine. A 2013 meta-analysis of eight studies demonstrated that cytisine has similar effectiveness to varenicline but with substantially lower side effects. A 2014 systematic review and economic evaluation concluded that cytisine was more likely to be cost-effective for smoking cessation than varenicline.
(-)-Cytisine, extracted from Laburnum anagyroides seeds was used as a starting material for the preparation of "(+)-sparteine surrogate," for the preparation of enantiomerically enriched lithium anions of opposite sterochemistry to those anions obtained from sparteine.
Excessive doses of cytisine can interfere with breathing and cause death (LD50 i.v., in mice ~2 mg/kg),. Māmane (Sophora chrysophylla) can contain amounts of cytisine that are lethal to most animals. 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 māmane, 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.
^Leaviss, Joanna; Sullivan, William; Ren, Shijie; Everson-Hock, Emma; Stevenson, Matt; Stevens, John; Strong, Mark; Cantrell, Anna (2014). "What is the clinical effectiveness and cost-effectiveness of cytisine compared with varenicline for smoking cessation? A systematic review and economic evaluation". Health Technology Assessment18 (33). doi:10.3310/hta18330.
^"Synthesis of (+)-(1R,@S,9S)-11-Methyl-7,11-Diazatricyclo[7.3.1.02.7]tridecane, a (+)sparteine surrogate". ORGANIC SYNTHESES83: 141. 2006. doi:10.15227/orgsyn.083.0141.