Cytisine

Cytisine at a Glance

Cytisine is a quinolizidine alkaloid of the legume family — broom, laburnum, wild indigo, Sophora, Thermopsis — and a partial agonist at α4β2 nicotinic acetylcholine receptors, the receptor subtype through which nicotine produces dependence ^{2Reference 2Rigotti NA · 2026ReviewAn evaluation of cytisinicline for smoking cessation in adult smokers — reviewView study →}.

That one property runs in both directions. It is why laburnum seeds poison children and why ingesting Baptisia from a garden produces weakness, vomiting and profound ataxia ^{7Reference 7Anderson MJ et al. · 2015Case reportBaptisia poisoning: a new and toxic look-alike in the neighborhood — case reportView study →}. It is also why cytisine has been sold in Bulgaria and across Eastern Europe as a low-cost smoking-cessation drug since the 1960s, and why a modern reformulation of it — cytisinicline — has now cleared two Phase 3 trials in the United States and is under FDA review ^{1,2Reference 1Rigotti NA et al. · 2025RCTCytisinicline for smoking cessation: the ORCA phase 3 replication randomized clinical trial — randomised placebo-controlled trialView study →Reference 2Rigotti NA · 2026ReviewAn evaluation of cytisinicline for smoking cessation in adult smokers — reviewView study →}.

The distinction that matters most about this molecule is the one between those two facts. The drug is not the herb. Cytisine’s efficacy is established at a precisely controlled 1.5–3 mg tablet dose on a defined schedule; broom, laburnum and wild indigo cannot be dosed to that, and the plants’ own literature is about poisoning, not smoking cessation.

The Drug Is Not the Plant

Cytisine’s own pharmacology is unusually well evidenced for a plant alkaloid — and almost none of that evidence belongs to any plant.

The drug side. Cytisine has been in continuous medical use in Eastern Europe for decades under a tapering 25-day regimen. A 2024 systematic review and meta-analysis found that people using cytisine were significantly more likely to quit tobacco than those receiving placebo, no intervention or usual care (RR 2.65, 95% CI 1.50–4.67; 6 trials, 5,194 participants) and more likely than those receiving nicotine replacement therapy (RR 1.36, 95% CI 1.06–1.73; 2 trials, 1,511 participants), with no statistically significant difference against varenicline (RR 0.96; 3 trials, 2,508 participants) ^{3Reference 3Puljević C et al. · 2024Meta-analysisSystematic review and meta-analyses of cytisine to support tobacco cessationView study →}. In the ORCA-3 Phase 3 replication trial, 792 US adults smoking ten or more cigarettes daily were randomised to cytisinicline 3 mg three times daily for 12 weeks, the same for 6 weeks, or placebo: 30.3% of the 12-week group were biochemically verified abstinent in weeks 9–12 against 9.4% on placebo (OR 4.4, 95% CI 2.6–7.3), with 20.5% versus 4.2% maintaining continuous abstinence to week 24 and no treatment-related serious adverse events ^{1Reference 1Rigotti NA et al. · 2025RCTCytisinicline for smoking cessation: the ORCA phase 3 replication randomized clinical trial — randomised placebo-controlled trialView study →}.

The plant side. Two people who ate Baptisia from a residential garden developed generalised nicotinic toxicity — weakness, gastrointestinal symptoms and profound ataxia ^{7Reference 7Anderson MJ et al. · 2015Case reportBaptisia poisoning: a new and toxic look-alike in the neighborhood — case reportView study →}. Laburnum seeds are a recognised cause of childhood poisoning. Cytisine has been quantified in post-mortem blood and urine in forensic casework, its over-the-counter availability in Eastern Europe making it a substance encountered in suicidal ingestion ^{8Reference 8Nowak K et al. · 2025Case reportMethod for determination of cytisine in post-mortem biological matrices and its application to two forensic cases — case seriesView study →}.

Between those two bodies of evidence there is no bridge. No plant preparation delivers a controlled 1.5 or 3 mg dose; no herbal use of broom, laburnum or wild indigo has ever been tested for smoking cessation; and the alkaloid content of those plants is not reliably quantified in the first place — for Baptisia tinctoria, cytisine is described only qualitatively as “present in all parts”. Broom’s traditional use is diuretic and cardiac, and it is attributed to different molecules — sparteine and the flavone glycoside scoparin.

What It's Used For

Cytisine is a partial agonist: it occupies the α4β2 nicotinic receptor and activates it weakly, which both blunts withdrawal (some agonism) and reduces the reward from smoking (blocking full agonism by nicotine) ^{2Reference 2Rigotti NA · 2026ReviewAn evaluation of cytisinicline for smoking cessation in adult smokers — reviewView study →}. Almost everything else in its literature is preclinical, and much of it is recent.

Evidence by IndicationStrength of support · Beta

01Smoking CessationProven82%Meta-analysis of RCTs plus two Phase 3 trials; decades of licensed use in Eastern Europe ^{1,2,3Reference 1Rigotti NA et al. · 2025RCTCytisinicline for smoking cessation: the ORCA phase 3 replication randomized clinical trial — randomised placebo-controlled trialView study →Reference 2Rigotti NA · 2026ReviewAn evaluation of cytisinicline for smoking cessation in adult smokers — reviewView study →Reference 3Puljević C et al. · 2024Meta-analysisSystematic review and meta-analyses of cytisine to support tobacco cessationView study →}

02Neuroprotection (Excitotoxicity)Shaky22%One in-vitro study in cultured cortical neurons, with a specific receptor-subunit mechanism ^{5Reference 5Li YJ et al. · 2013In vitroCytisine confers neuronal protection against excitotoxic injury by down-regulating GluN2B-containing NMDA receptors — in vitroView study →}

03Antidepressant-Like ActivityShaky20%One mouse chronic-mild-stress model with hippocampal protein readouts ^{6Reference 6Han J et al. · 2016AnimalCytisine, a partial agonist of α4β2 nicotinic acetylcholine receptors, reduced unpredictable chronic mild stress-induced depression-like behaviors — animal modelView study →}

04Anxiolytic Activity (Derivatives)Shaky12%Zebrafish behavioural work on halogenated derivatives, not on cytisine itself ^{9Reference 9Farías-Cea A et al. · 2023AnimalBehavioral study of 3- and 5-halocytisine derivatives in zebrafish using the novel tank diving test — animal modelView study →}

Mechanisms

Rows one and six are the same receptor. The therapeutic dose is milligrams on a schedule; the poisoning dose is however much of a plant somebody ate.

Pharmacokinetics

Cytisine is orally active — that is the basis of its entire clinical use — and its pharmacology and pharmacokinetics have been reviewed in detail ^{4Reference 4Wang X et al. · 2024ReviewCytisine: state of the art in pharmacological activities and pharmacokinetics — reviewView study →}. It is a small, polar alkaloid, and its clinical profile is shaped by a short duration of action, which is why the traditional Eastern European regimen requires six doses a day and why the modern cytisinicline regimen is three times daily rather than once ^{2Reference 2Rigotti NA · 2026ReviewAn evaluation of cytisinicline for smoking cessation in adult smokers — reviewView study →}.

The two dosing schedules are worth distinguishing, because they are the same molecule differently deployed. The traditional regimen is a 25-day taper beginning at 1.5 mg six times daily and stepping down. The cytisinicline regimen tested in the Phase 3 trials is 3 mg three times daily for 6 or 12 weeks ^{1,2Reference 1Rigotti NA et al. · 2025RCTCytisinicline for smoking cessation: the ORCA phase 3 replication randomized clinical trial — randomised placebo-controlled trialView study →Reference 2Rigotti NA · 2026ReviewAn evaluation of cytisinicline for smoking cessation in adult smokers — reviewView study →}. Analytical methods for measuring cytisine in blood and urine have been developed for clinical and forensic use ^{8Reference 8Nowak K et al. · 2025Case reportMethod for determination of cytisine in post-mortem biological matrices and its application to two forensic cases — case seriesView study →}.

Clinical Trials

Cytisine is one of very few plant alkaloids with a modern Phase 3 programme behind it.

Last checked: September 2026.

Isolate vs. Plant Studies

This is the sharpest isolate-versus-plant split of any alkaloid on the site, because both sides of it are well documented and they do not meet.

The isolate is a licensed drug. Every efficacy figure above comes from purified cytisine formulated as a tablet at a specified milligram dose, in randomised trials with biochemically verified endpoints ^{1,3Reference 1Rigotti NA et al. · 2025RCTCytisinicline for smoking cessation: the ORCA phase 3 replication randomized clinical trial — randomised placebo-controlled trialView study →Reference 3Puljević C et al. · 2024Meta-analysisSystematic review and meta-analyses of cytisine to support tobacco cessationView study →}. That is a genuine strength — this is not a molecule whose reputation is borrowed from an extract.

The plants are poisoning references. Baptisia tinctoria, Laburnum anagyroides and Cytisus scoparius appear in the clinical literature for nicotinic toxicity, not for cessation ^{7,8Reference 7Anderson MJ et al. · 2015Case reportBaptisia poisoning: a new and toxic look-alike in the neighborhood — case reportView study →Reference 8Nowak K et al. · 2025Case reportMethod for determination of cytisine in post-mortem biological matrices and its application to two forensic cases — case seriesView study →}. And the herbs’ own therapeutic reputations rest elsewhere: wild indigo’s best-supported activity belongs to its arabinogalactan-proteins and polysaccharides, high-molecular-weight root fractions that are not small molecules at all; broom’s traditional diuretic use is credited to scoparin and its cardiac effects to sparteine.

So cytisine is a case where the molecule earned a clinical record its source plants have no claim on — and where the plants’ own risk is created by the same molecule. Anyone reading the cessation evidence as a reason to take broom has the relationship exactly backwards.

Prevalence in Nature

Cytisine is a Fabaceae alkaloid, distributed across the quinolizidine-producing legumes and often accompanied by sparteine, lupanine and N-methylcytisine ^{4Reference 4Wang X et al. · 2024ReviewCytisine: state of the art in pharmacological activities and pharmacokinetics — reviewView study →}.

Its richest documented source is laburnum (Laburnum anagyroides) seed, which is the reason laburnum is one of the more frequently reported ornamental poisonings in Europe. It occurs throughout broom (Cytisus scoparius) and its relatives in Genista and Ulex — the old name ulexine records its isolation from gorse — and in wild indigo (Baptisia tinctoria), where the older literature calls it baptitoxine or baptisine and describes it as present in all parts of the plant. It is also found in Sophora and Thermopsis species, the latter giving it the synonym sophorine.

Quantitative figures are largely absent. For Baptisia tinctoria in particular, no verifiable constituent concentrations exist — cytisine is described only qualitatively. That is not a minor gap: it is the reason no plant preparation can be dosed, and it is why the therapeutic and toxic literatures cannot be reconciled at the level of the herb.

Discovery & Synthesis

Cytisine belongs to the classical nineteenth-century Fabaceae alkaloid chemistry, and its several names record the several plants it was isolated from independently — ulexine from gorse, sophorine from Sophora, baptitoxine and baptisine from Baptisia. Structurally it is a compact bispidine-fused quinolizidine bearing a pyridone ring, which is what gives it the rigid, nicotine-mimicking geometry the receptor responds to.

Its medical history is Eastern European. Cytisine has been used as a nicotine substitute since around the Second World War and marketed as a smoking-cessation aid from the 1960s, most familiarly as Tabex ^{2,10Reference 2Rigotti NA · 2026ReviewAn evaluation of cytisinicline for smoking cessation in adult smokers — reviewView study →Reference 10Rubio FR et al. · 2023ReviewPotential uses of cytisine for smoking cessation in menopausal women — literature reviewView study →}. It remained essentially invisible to Western medicine for fifty years — cheap, off-patent, and unstudied by the standards Western regulators require — until a series of randomised trials from about 2011 onward brought it into the mainstream evidence base ^{3Reference 3Puljević C et al. · 2024Meta-analysisSystematic review and meta-analyses of cytisine to support tobacco cessationView study →}. Varenicline, the licensed α4β2 partial agonist developed in the West for the same indication, arrived at the same receptor target by a different route ^{11Reference 11Coe JW et al. · 2005Varenicline: an alpha4beta2 nicotinic receptor partial agonist for smoking cessationView study →}.

The current chapter is cytisinicline: not a new molecule but a new dosing regimen of cytisine, taken through two Phase 3 trials in US adults, with a New Drug Application now before the FDA ^{1,2Reference 1Rigotti NA et al. · 2025RCTCytisinicline for smoking cessation: the ORCA phase 3 replication randomized clinical trial — randomised placebo-controlled trialView study →Reference 2Rigotti NA · 2026ReviewAn evaluation of cytisinicline for smoking cessation in adult smokers — reviewView study →}. Manufacture has historically been by extraction from Laburnum seed rather than by synthesis, and cytisine’s low cost relative to the other drugs in its class is one of the recurring arguments for its use ^{3,10Reference 3Puljević C et al. · 2024Meta-analysisSystematic review and meta-analyses of cytisine to support tobacco cessationView study →Reference 10Rubio FR et al. · 2023ReviewPotential uses of cytisine for smoking cessation in menopausal women — literature reviewView study →}.

Patents: not yet researched.

Toxicity & Safety

Cytisine carries a toxic flag, and the reason is the same receptor that makes it useful.

At therapeutic doses it is well tolerated. The Phase 3 trials reported no treatment-related serious adverse events across 792 participants, with nausea, abnormal dreams and insomnia the commonest complaints ^{1Reference 1Rigotti NA et al. · 2025RCTCytisinicline for smoking cessation: the ORCA phase 3 replication randomized clinical trial — randomised placebo-controlled trialView study →}; the meta-analysed trials are consistent with that ^{3Reference 3Puljević C et al. · 2024Meta-analysisSystematic review and meta-analyses of cytisine to support tobacco cessationView study →}.

At plant doses it is a nicotinic poison. Ingestion produces the nicotinic toxidrome: generalised weakness, nausea and vomiting, abdominal pain, sweating, headache, tachycardia and — a feature specifically noted in Baptisia poisoning and attributed to nicotinic receptor subunits in the cerebellum — profound ataxia ^{7Reference 7Anderson MJ et al. · 2015Case reportBaptisia poisoning: a new and toxic look-alike in the neighborhood — case reportView study →}. Severe cases progress to convulsions and respiratory difficulty. Cytisine’s over-the-counter availability in parts of Europe has also made it a substance of deliberate overdose, and analytical methods now exist for identifying it in post-mortem blood and urine ^{8Reference 8Nowak K et al. · 2025Case reportMethod for determination of cytisine in post-mortem biological matrices and its application to two forensic cases — case seriesView study →}.

Safety at a Glance

☠️ Toxic

• Well tolerated as a dosed medicine. No treatment-related serious adverse events in a 792-participant Phase 3 trial; nausea, abnormal dreams and insomnia are the usual complaints.
• The source plants are poisonous. Laburnum seed and Baptisia cause nicotinic toxicity — weakness, vomiting, tachycardia and profound ataxia — and their cytisine content is not quantified or dose-controllable.
• Deliberate overdose is documented, including fatal forensic cases, and cytisine is detectable in post-mortem blood and urine.
• Not established in pregnancy or lactation. Nicotinic receptor agonism during development is a real concern and the trials excluded these populations.
• The cessation evidence does not transfer to any herbal preparation. Every efficacy figure comes from a milligram-precise tablet on a defined schedule.

Full Safety & Interactions Detail

Acute toxicity. Cytisine is a nicotinic acetylcholine receptor agonist, and poisoning reproduces nicotine poisoning: gastrointestinal symptoms first (nausea, vomiting, abdominal pain), then generalised weakness, sweating, headache, tachycardia and hypertension, with ataxia prominent enough in Baptisia cases to be a diagnostic clue ^{7Reference 7Anderson MJ et al. · 2015Case reportBaptisia poisoning: a new and toxic look-alike in the neighborhood — case reportView study →}. Severe poisoning may progress to seizures and respiratory compromise. Management is supportive; there is no specific antidote.

Which plants, and why it matters. Laburnum seed is the classic paediatric ornamental poisoning in Britain and Europe. Baptisia tinctoria is increasingly planted in residential and restored-prairie settings, which is exactly the point the emergency-medicine case report was making — it is a new look-alike in gardens where people do not expect a poisonous plant ^{7Reference 7Anderson MJ et al. · 2015Case reportBaptisia poisoning: a new and toxic look-alike in the neighborhood — case reportView study →}. Broom carries cytisine alongside sparteine, a cardioactive sodium-channel blocker with its own toxicity, so a broom overdose is not a single-alkaloid event.

Forensic and intentional exposure. Cytisine’s low cost and over-the-counter status in Eastern Europe make it accessible, and a 2025 forensic-toxicology study developed a validated method for cytisine in post-mortem blood and urine specifically because of casework requiring it ^{8Reference 8Nowak K et al. · 2025Case reportMethod for determination of cytisine in post-mortem biological matrices and its application to two forensic cases — case seriesView study →}.

Drug interactions. No major pharmacokinetic interaction profile is established. On mechanism, concurrent nicotine (smoking, patches, vaping) is the obvious pharmacodynamic interaction — cytisine competes at the same receptor, which is the therapeutic point but also means combined use is not additive in the way a naive reading might suggest. Combining with varenicline, which acts at the same site, has no rationale.

Pregnancy and lactation. Not established. The cessation trials excluded pregnant participants, and nicotinic receptor agonism during neurodevelopment is a substantive concern rather than a formality. Decisions about intake are made at the herb or product level, not at the molecule level; the finding stated here is that no adequate data exist.

Cardiovascular. Nicotinic agonism raises heart rate and blood pressure. The Phase 3 trials in adults who smoked did not identify cardiovascular safety signals at the studied dose ^{1Reference 1Rigotti NA et al. · 2025RCTCytisinicline for smoking cessation: the ORCA phase 3 replication randomized clinical trial — randomised placebo-controlled trialView study →}, but the acute toxidrome is cardiovascular in part.

Dosage

Cytisine’s doses are pharmaceutical and precise, which is exactly why they cannot be reached with a plant.

The third row is the one to read. There is no herbal dose of cytisine, because there is no reliable content figure for any of the source plants and no preparation designed to deliver a milligram target. These are the doses used in research and licensed practice, and they are not a personal recommendation.

References

1. Rigotti NA, Benowitz NL, Prochaska JJ, et al. (2025). Cytisinicline for smoking cessation: the ORCA phase 3 replication randomized clinical trial — randomised placebo-controlled trial. JAMA Internal Medicine. https://pubmed.ncbi.nlm.nih.gov/40257755/
2. Rigotti NA, Benowitz NL (2026). An evaluation of cytisinicline for smoking cessation in adult smokers — review. Expert Opinion on Pharmacotherapy. https://pubmed.ncbi.nlm.nih.gov/41885781/
3. Puljević C, Stjepanović D, Meciar I, et al. (2024). Systematic review and meta-analyses of cytisine to support tobacco cessation. Addiction. https://pubmed.ncbi.nlm.nih.gov/38965792/
4. Wang X, Yang J, Huang P, et al. (2024). Cytisine: state of the art in pharmacological activities and pharmacokinetics — review. Biomedicine & Pharmacotherapy. https://pubmed.ncbi.nlm.nih.gov/38271893/
5. Li YJ, Yang Q, Zhang K, et al. (2013). Cytisine confers neuronal protection against excitotoxic injury by down-regulating GluN2B-containing NMDA receptors — in vitro. Neurotoxicology. https://pubmed.ncbi.nlm.nih.gov/23022271/
6. Han J, Wang DS, Liu SB, Zhao MG (2016). Cytisine, a partial agonist of α4β2 nicotinic acetylcholine receptors, reduced unpredictable chronic mild stress-induced depression-like behaviors — animal model. Biomolecules & Therapeutics. https://pubmed.ncbi.nlm.nih.gov/27098858/
7. Anderson MJ, Kurtycz DF, Cline JR (2015). Baptisia poisoning: a new and toxic look-alike in the neighborhood — case report. The Journal of Emergency Medicine. https://pubmed.ncbi.nlm.nih.gov/25453859/
8. Nowak K, Szpot P, Zawadzki M, Chłopaś-Konowałek A (2025). Method for determination of cytisine in post-mortem biological matrices and its application to two forensic cases — case series. Forensic Toxicology. https://pubmed.ncbi.nlm.nih.gov/39695055/
9. Farías-Cea A, Leal C, Hödar-Salazar M, et al. (2023). Behavioral study of 3- and 5-halocytisine derivatives in zebrafish using the novel tank diving test — animal model. International Journal of Molecular Sciences. https://pubmed.ncbi.nlm.nih.gov/37445811/
10. Rubio FR, Martínez FM, Romero MJZ (2023). Potential uses of cytisine for smoking cessation in menopausal women — literature review. Przegląd Menopauzalny. https://pubmed.ncbi.nlm.nih.gov/37206678/
11. Coe JW, Brooks PR, Vetelino MG, et al. (2005). Varenicline: an alpha4beta2 nicotinic receptor partial agonist for smoking cessation. Journal of Medicinal Chemistry. https://pubmed.ncbi.nlm.nih.gov/15887955/

View all 11 references▾