Compound Monograph
Anethole
Anethole (trans-anethole) is the sweet phenylpropanoid behind fennel, anise and star anise — a carminative, mild phytoestrogen and TRPA1 agonist, GRAS as a flavoring but hepatotoxic at high doses. Not to be confused with its carcinogen-flagged isomer estragole.
Sources · 5
Where Does It Come From?
Anethole is a synthetic phenylpropanoid (methoxylated propenylbenzene), found in Fennel, Anise, Star anise and 2 other sources. It is flagged as moderately toxic.
Principal source Fennel Foeniculum vulgare Herb monograph → 
Source Mexican Tarragon Tagetes lucida Herb monograph → 
Source Tarragon Artemisia dracunculus Herb monograph → Concentration
Content by Source
Concentrations not reported. No percent-dry-weight or mg/g figures have been published for this compound in its source plants.
Anethole at a Glance
Anethole (trans-anethole) is the sweet phenylpropanoid behind fennel, anise and star anise — the compound responsible for that distinctive liquorice-like taste and for their traditional carminative use.
Pharmacologically it is a mild phytoestrogen and a TRPA1 agonist, the latter explaining much of its effect on gut motility and sensation. It is GRAS as a flavouring, and hepatotoxic at high doses — a genuine dose ceiling rather than a theoretical one.
It should not be confused with its isomer cis-anethole, which is flagged for carcinogenicity; the two differ only in geometry around one double bond.
What It's Used For
Anethole (trans-anethole) is the sweet phenylpropanoid that gives fennel, anise and star anise their flavor, and the dominant volatile of fennel seed oil. Two disambiguations matter before any claim. It is not estragole (methylchavicol) — its carcinogen-flagged positional isomer, a separate compound — and its estrogenic reputation is often attributed to its dimers dianethole and photoanethole, not the monomer. Its best-defined action is carminative/GI-antispasmodic: it relaxes gut smooth muscle and restores delayed gastric emptying 1Reference 1AnimalAnethole restores delayed gastric emptying and impaired gastric accommodation in rodentsView study →.
But two things frame the evidence — all human GI, menstrual and lactation outcomes are for the whole fennel/anise herb or oil, not purified anethole, and while it is GRAS as a flavoring, it is hepatotoxic at high doses via a reactive epoxide metabolite 14Reference 14AnimalMetabolic activation of trans-anethole plays a role in hepatic cytotoxicity in miceView study →.
Support is an experimental score — weighted by study type (human > animal > in vitro) and volume. A beta, not a validated metric. Human data are for the herb, not the isolate, so isolate scores stay modest. Each application links to its write-up.
Fennel and anise’s core traditional use. trans-Anethole relaxes GI smooth muscle by inhibiting store-operated Ca²⁺ influx and restores delayed gastric emptying and impaired accommodation in rodents 1Reference 1AnimalAnethole restores delayed gastric emptying and impaired gastric accommodation in rodentsView study →, and fennel tea shows a region-specific effect on human stomach motility 2Reference 2Fennel tea has a region-specific effect on the motility of the stomachView study →, consistent with the broader fennel pharmacology 17Reference 17Foeniculum vulgare Mill: botany, phytochemistry, pharmacology and toxicologyView study →. Anethole is also a selective, non-electrophilic TRPA1 agonist, which underlies some of its sensory, topical and gut-signaling effects 11,
Gap: the isolate’s antispasmodic data are preclinical, and all human evidence is the whole herb/oil, not purified trans-anethole 1,
Anethole is the long-standing basis of fennel/anise’s phytoestrogen and galactagogue reputation, with the classic hypothesis attributing activity to the dimers dianethole and photoanethole and a dopamine-antagonist/prolactin route 3Reference 3Fennel and anise as estrogenic agentsView study →; dietary fennel oil shifts reproductive-axis hormones in animals 4Reference 4Effect of encapsulated fennel-seed essential oil on serum hormones and reproductive-axis genes in laying hensView study →.
Gap: the direct receptor-binding potency of monomeric trans-anethole is weak and inconsistent — the “active” species may be dimers or metabolites — and the emmenagogue/estrogenic claims are traditional and animal, not controlled human data 3,
Anethole-dominant essential oils (star anise, fennel, Ammi) show antibacterial activity with membrane-disruption and docking rationales 6,
Gap: the activity is reported for the whole essential oil, and isolated trans-anethole MICs are moderate — do not overstate isolate potency 6,
Reviewed as an NF-κB and cytokine suppressor across chronic-disease models 8Reference 8Anethole and its role in chronic diseasesView study →, anethole attenuated doxorubicin cardio-/nephrotoxicity in a network-pharmacology-mapped animal study 9Reference 9Anethole alleviates doxorubicin-induced cardiac and renal toxicitiesView study → and was neuroprotective against aluminum-induced memory impairment via AChE, oxidative stress and NLRP3 10Reference 10Neuroprotective effects of trans-anethole on aluminium-chloride-induced memory impairment (AChE, oxidative stress, NLRP3)View study →.
Gap: entirely preclinical (rodent/in-vitro/in-silico), with dose- and model-specific effects 8,
Anethole shows apoptosis and NF-κB-linked antiproliferative effects across cell lines, as reviewed 8Reference 8Anethole and its role in chronic diseasesView study →.
Gap: in-vitro and early-animal only, at high doses, with no human or in-vivo tumor efficacy of the isolate — strictly preclinical 8Reference 8Anethole and its role in chronic diseasesView study →.
Mechanisms
| Target / pathway | Effect | Relevant to |
|---|---|---|
| Store-operated Ca²⁺ channels (GI smooth muscle) | ↓ Ca²⁺ influx → relaxation; restores gastric emptying | carminative / antispasmodic / prokinetic |
| TRPA1 ion channel | selective, non-electrophilic agonist | sensory pharmacologyGI signaling |
| Estrogen-like signaling (via dianethole/photoanethole dimers) + dopamine antagonism → ↑ prolactin | weak phytoestrogen / galactagogue | lactationmenstrualhormone caution |
| NF-κB / cytokines; NLRP3 inflammasome; AChE | ↓ inflammatory mediators; enzyme inhibition | anti-inflammatoryneuroprotection |
| Microbial membrane integrity | disruption (essential-oil level) | antimicrobial |
Pharmacokinetics
trans-Anethole is rapidly and near-completely absorbed and metabolized. The propenyl side chain undergoes ω-oxidation to 4-methoxybenzoic (anisic) acid derivatives, alongside O-demethylation and conjugation (glucuronide/sulfate/glycine), with the bulk excreted in urine within 24 hours 13Reference 13AnimalThe metabolism of anetholeView study →. A minor route is epoxidation to anethole-1′,2′-epoxide, the reactive metabolite implicated in high-dose hepatotoxicity 14Reference 14AnimalMetabolic activation of trans-anethole plays a role in hepatic cytotoxicity in miceView study →. Crucially the metabolism is dose-dependent: detoxifying conjugation dominates at low (flavoring) doses, while the epoxide pathway becomes proportionally larger at high doses — which is why the hepatotoxicity is a high-dose, threshold phenomenon rather than a flavoring-level concern.
Clinical trials
All human evidence is for the herb/oil, not purified trans-anethole: fennel tea alters human gastric motility 2Reference 2Fennel tea has a region-specific effect on the motility of the stomachView study →, and fennel/anise preparations are used for dysmenorrhea, IBS/infantile colic and as galactagogues (the lactation evidence and its limits are summarized in the LactMed monograph) 5Reference 5Drugs and Lactation Database (LactMed)View study → — outcomes that reflect the multi-constituent oil and cannot be attributed to trans-anethole alone. There is no controlled trial of isolated trans-anethole in humans.
| Completed | Planned | Terminated | Preclinical |
|---|---|---|---|
| —(isolate); fennel/anise herb only | — | — | Extensive |
Last checked: July 2026.
Toxicity & Safety
Anethole is a GRAS flavoring at culinary exposure, and the whole safety story is dose — the liver toxicity is a high-dose threshold effect, and the carcinogen flag people attach to it actually belongs to its isomer estragole.
- GRAS at flavoring levels. Culinary and flavoring exposure is considered low-risk, with a defined JECFA intake limit.
- Hepatotoxic at high doses. Chronic high oral doses cause dose-related liver toxicity in rodents via a reactive epoxide metabolite.
- Not estragole. The genotoxic/carcinogenic classification belongs to that separate positional isomer, not to trans-anethole.
- Estrogenic caution. The phytoestrogen and emmenagogue reputation warrants care in hormone-sensitive conditions.
- Avoid concentrated oil in pregnancy. Culinary amounts are a different matter.
Full Safety & Interactions Detail
trans-Anethole is an approved GRAS flavoring at low intake (a JECFA group ADI of roughly 0–2 mg/kg body weight), and at culinary/flavoring exposure is considered low-risk. Three qualifiers define the rest. (1) High-dose hepatotoxicity: chronic high oral doses cause dose-related liver toxicity in rodents, driven by metabolic activation to anethole-1′,2′-epoxide — a high-dose, threshold phenomenon, not a flavoring-level concern 14Reference 14AnimalMetabolic activation of trans-anethole plays a role in hepatic cytotoxicity in miceView study →.
(2) Estragole context (do not conflate): the positional isomer estragole is genotoxic/carcinogenic as an isolate 15Reference 15Cytotoxic, genotoxic and apoptosis-inducing effects of estragole from fennelView study →, while whole-fennel-matrix exposure is argued to be far lower risk 16Reference 16Can estragole in fennel-seed decoctions really be considered a danger for human health? A fennel safety updateView study → — but trans-anethole itself is not classified as a genotoxic carcinogen and has its own defined intake limit, so the carcinogen flag belongs to the separate estragole page. (3) Estrogenic caution: the phytoestrogen/emmenagogue reputation warrants caution in hormone-sensitive conditions 3Reference 3Fennel and anise as estrogenic agentsView study →.
(The cis-isomer is markedly more toxic than trans-, but commercial and natural material is predominantly trans.)
Dosage
There is no established therapeutic dose for isolated trans-anethole, and nothing here is a recommendation. The firm regulatory anchor is a JECFA ADI of ~0–2 mg/kg body weight/day as a flavoring — a safety ceiling, not an efficacy dose. Traditional herb dosing (fennel seed ~1.5–2.5 g as an infusion, one to three times daily; essential oil much lower) delivers anethole as one component of a mixture.
References
- Asano T, et al. (2016). Anethole restores delayed gastric emptying and impaired gastric accommodation in rodents. Biochemical and Biophysical Research Communications. https://pubmed.ncbi.nlm.nih.gov/26915803/
- Annaházi A, et al. (2025). Fennel tea has a region-specific effect on the motility of the stomach. Neurogastroenterology & Motility. https://pubmed.ncbi.nlm.nih.gov/41214408/
- Albert-Puleo M (1980). Fennel and anise as estrogenic agents. Journal of Ethnopharmacology. https://pubmed.ncbi.nlm.nih.gov/6999244/
- İpçak HH, Denli M, Yokuş B, et al. (2025). Effect of encapsulated fennel-seed essential oil on serum hormones and reproductive-axis genes in laying hens. Veterinary Medicine and Science. https://pubmed.ncbi.nlm.nih.gov/39655356/
- Fennel. Drugs and Lactation Database (LactMed). https://pubmed.ncbi.nlm.nih.gov/30000852/
- Yang EC, Hsieh YY, Chuang LY (2021). Phytochemical composition and antibacterial activities of extracts from Illicium verum (star anise). Molecules. https://pubmed.ncbi.nlm.nih.gov/34206777/
- Khammassi M, Polito F, Caputo L, et al. (2024). Antibacterial/antibiofilm profiles and docking of Ammi visnaga and Foeniculum vulgare essential-oil components. Fitoterapia. https://pubmed.ncbi.nlm.nih.gov/38838824/
- Aprotosoaie AC, et al. (2016). Anethole and its role in chronic diseases. Advances in Experimental Medicine and Biology. https://pubmed.ncbi.nlm.nih.gov/27771928/
- Al-Ali MA, Younis NS, Aldhubiab B, et al. (2024). Anethole alleviates doxorubicin-induced cardiac and renal toxicities. Chemico-Biological Interactions. https://pubmed.ncbi.nlm.nih.gov/39029857/
- Bagwe Parab S, Tripathi P, Barve K, et al. (2026). Neuroprotective effects of trans-anethole on aluminium-chloride-induced memory impairment (AChE, oxidative stress, NLRP3). Metabolic Brain Disease. https://pubmed.ncbi.nlm.nih.gov/42154340/
- Memon T, Yarishkin O, Reilly CA, et al. (2019). trans-Anethole of fennel oil is a selective and non-electrophilic agonist of the TRPA1 ion channel. Molecular Pharmacology. https://pubmed.ncbi.nlm.nih.gov/30679204/
- Santos LG, de Oliveira JRJM, Amorim MA, et al. (2024). Role of TRPA1 in the effect of topical trans-anethole in mice. Naunyn-Schmiedeberg’s Archives of Pharmacology. https://pubmed.ncbi.nlm.nih.gov/38809294/
- Sangster SA, et al. (1984). The metabolism of anethole. I. Pathways of metabolism in the rat and mouse. Food and Chemical Toxicology. https://pubmed.ncbi.nlm.nih.gov/6541622/
- Shen Y, Wang Y, Sun S, et al. (2025). Metabolic activation of trans-anethole plays a role in hepatic cytotoxicity in mice. Journal of Agricultural and Food Chemistry. https://pubmed.ncbi.nlm.nih.gov/40069955/
- Villarini M, et al. (2014). Cytotoxic, genotoxic and apoptosis-inducing effects of estragole from fennel. Journal of Natural Products. https://pubmed.ncbi.nlm.nih.gov/24617303/
- Gori L, et al. (2012). Can estragole in fennel-seed decoctions really be considered a danger for human health? A fennel safety update. Evidence-Based Complementary and Alternative Medicine. https://pubmed.ncbi.nlm.nih.gov/22899959/
- Badgujar SB, et al. (2014). Foeniculum vulgare Mill: botany, phytochemistry, pharmacology and toxicology. BioMed Research International. https://pubmed.ncbi.nlm.nih.gov/25162032/
