Ayurveda · Traditional Chinese medicine · Western herbalism

FennelFoeniculum vulgare

Q: Does fennel help infant colic?

One placebo-controlled trial of 125 infants found a fennel oil emulsion eliminated colic in 65% against 23.7% on placebo. A review of 15 colic trials said fennel extract had encouraging results but that every trial had major limitations. The European monograph does not advise fennel tea under age 4.

Q: Is fennel tea safe to drink every day?

The European monograph limits use to 2 weeks in adults and under one week for children 4 to 12. A safety assessment found low priority for risk management in adults who drink one cup a day, mainly because of estragole, and a higher priority for children. Whole fruit infusions contained about three times less estragole than fine-cut material.

Q: Are fennel and anise the same?

No. They are separate plants in the same family, and both contain anethole. The European monograph lists allergy to anise, caraway, celery, coriander or dill as a reason for care with fennel.

Q: Does fennel help IBS or constipation?

The adult trials we found used fennel inside mixtures: curcumin plus fennel oil in 121 people with IBS, and fennel plus rose in 50 older adults with constipation. Both beat their comparison, but neither isolates fennel. We could not find a trial of fennel alone for adult gut symptoms.

The seed chewed after meals; one infant colic trial (125 babies) found colic gone in 65% vs 23.7% on placebo, and adult gut trials are of mixtures.

Botanical name: Foeniculum vulgare
Part used: fruit (the seed)
Also called: Sanskrit Madhurika, Mishreya; Hindi Saunf; pinyin Xiao hui xiang (小茴香); Bitter fennel, Sweet fennel, Foeniculi fructus
Used in: Ayurveda, Traditional Chinese medicine, Western herbalism
Taken for: Gas, Bloating, Cramping and pain, Indigestion
Sold as: tea, whole seed, capsules, essential oil, extract

Fennel, the plant and the part used

Fennel is a tall, feathery perennial of the carrot family (Apiaceae), native to the Mediterranean shore and now grown worldwide. The part used for the gut is the dry fruit, which is called the seed in the kitchen: small, ridged, greenish-brown and strongly aromatic. Two types exist. Bitter fennel and sweet fennel are separate varieties, and the European herbal committee has issued a monograph for each; the bitter type is the one the monograph quoted here covers.

For the gut, fennel is used as whole or crushed seeds chewed or steeped in hot water (the European monograph steeps 1.5 g in 250 ml of boiling water for 15 minutes), as capsules of ground seed or extract, and as an essential oil emulsion. In India the seeds are served after meals; in Chinese medicine the dry fruit goes into decoctions.

Its chemistry matters for how it is sold. The oil is mostly trans-anethole, with fenchone and a smaller amount of estragole, and the estragole content of dry fennel varies widely between batches.

Traditional uses, in their own terms

Ayurveda (about Ayurveda)

Fennel is known in Sanskrit as madhurika, and reviews report that Indian traditional medicine regards it as aromatic, stimulant and stomachic (a digestive aid for the stomach). The Ayurvedic Pharmacopoeia of India lists fennel as part of polyherbal formulas, and folk records from India describe a decoction of the fresh fruit for flatulence. We could not read the classical taste and potency classification in a source we could cite, so we do not state it here.

Traditional Chinese medicine (about TCM)

Xiao hui xiang is classed in Chinese medicine as warm and pungent, entering the liver, kidney, spleen and stomach channels. A Hong Kong Department of Health materia medica sheet gives its actions as dispelling cold and relieving pain, and regulating qi and strengthening the stomach. A university herb database lists abdominal cold pain with cold extremities, cold-type menstrual pain, and epigastric distending pain with poor appetite, vomiting and diarrhea among its indications, all in TCM terms of cold in the interior. It is also listed for hydrocele of the tunica vaginalis, a non-gut use.

Western herbalism

Fennel seed is a classic European carminative (a remedy for wind and bloating). The European Medicines Agency’s herbal committee lists bitter fennel fruit as a traditional herbal medicine, based on long-standing use alone, for mild spasmodic gastrointestinal complaints including bloating and flatulence, for minor spasm with menstrual periods, and as an expectorant in cough with a cold. Ethnobotanical records from the Mediterranean list fennel as a carminative and a seed decoction for constipation and digestive ailments.

Compounds, and what the laboratory says about them

The oil of fennel fruit is dominated by trans-anethole (roughly 60 to 90% across analyses), with fenchone (about 0.1 to 15%) and estragole (roughly 0.1 to 10%), depending on variety and extraction. A review of the plant reports that the oil regulates the motility of intestinal smooth muscle while reducing intestinal gas, a laboratory and animal finding. Estragole is the regulatory concern: it is considered a genotoxic carcinogen in rodents, which is why the European monograph limits the duration and the daily exposure for children. Analysis of marketed fennel teas found 0.15 to 13.3 mg of estragole per gram of dry material.

Trials in people, with the numbers

The best-controlled fennel trial is in infants, not adults. In 125 colicky infants aged 2 to 12 weeks, a fennel seed oil emulsion eliminated colic (cumulative crying under 9 hours a week) in 65% (40 of 62) against 23.7% (14 of 59) on placebo, a 41% absolute difference (95% CI 25 to 57) and a number needed to treat of 2; no side effects were reported. A separate placebo-controlled trial of 93 breastfed infants gave an extract of chamomile, fennel and lemon balm for one week and found crying fell from 201 to 77 minutes a day, against 199 to 170 on placebo, but that trial cannot isolate fennel. A systematic review of 15 trials of complementary treatments for colic found encouraging results for fennel extract but said all trials had major limitations, and a pediatric review found evidence for several fennel preparations in colic with no serious adverse events.

For adults the evidence comes from combinations. In 121 people with mild to moderate IBS, a capsule of curcumin plus fennel essential oil twice daily for 30 days reduced the symptom severity score by 50.05% against 26.12% on placebo (P < 0.001), and 25.9% against 6.8% were symptom-free. In 50 adults over 60 with functional constipation, a 10 g sachet of fennel plus Damask rose twice daily for 4 weeks improved severity, stool consistency and quality of life more than polyethylene glycol, with fewer side effects. In both, fennel was one of two ingredients, so neither trial shows what fennel does alone. We could not find a randomized trial of fennel tea or seed alone for adult bloating or gas.

Study	Dose	What it found
Randomized placebo-controlled trial, 125 infants with colic PMID 12868253	Fennel seed oil emulsion	Colic eliminated in 65% vs 23.7% on placebo (ARR 41%, 95% CI 25 to 57; NNT 2); no side effects reported
Randomized trial of a chamomile, fennel and lemon balm extract, 93 breastfed colicky infants (a mixture) PMID 16041731	Twice daily for 1 week	Crying time down in 85.4% vs 48.9% on placebo (P < 0.005); 201 to 77 min/day vs 199 to 170
Randomized trial of curcumin plus fennel essential oil, 121 adults with IBS (a combination) PMID 27308645	2 capsules twice daily for 30 days	Severity score down 50.05% vs 26.12% on placebo (P < 0.001); symptom-free 25.9% vs 6.8%
Randomized active-controlled trial of fennel plus Damask rose, 50 adults over 60 with functional constipation (a combination) PMID 35339396	10 g sachet twice daily for 4 weeks	Better severity, stool form and quality of life than PEG 4000, with fewer side effects
Systematic review of 15 randomized trials of complementary treatments for infantile colic PMID 21444591	Various	Encouraging results for fennel extract, mixed herbal tea and sugar solutions; all trials had major limitations

The doses on record

The European monograph’s traditional-use tea is 1.5 g of bitter fennel fruit in 250 ml of boiling water, steeped for 15 minutes, three times daily (4.5 g a day) for adults and adolescents, and 1.0 g in 100 ml three times daily for children 4 to 12. It limits use to 2 weeks in adults and under one week in children 4 to 12, and does not advise it under age 4.

Trials used mixtures: a 10 g sachet of fennel plus rose twice daily for 4 weeks, and capsules of curcumin plus fennel oil twice daily for 30 days. The colic trial used an oil emulsion. We could not find a Chinese pharmacopoeial dose we can cite.

None of this is a dose recommendation. It is what the literature used, set down so a label can be compared with it; a pharmacist or clinician decides what applies to you.

The safety record

The European monograph names allergy as the main adverse effect: skin or respiratory reactions to fennel, with cross-reactivity in people allergic to other Apiaceae (anise, caraway, celery, coriander, dill), to anethole, or to mugwort pollen. A Hong Kong herb database also lists asthma, contact dermatitis and rhinoconjunctivitis. Safety in pregnancy and lactation has not been established, and the monograph says use in pregnancy and breastfeeding is not advised; trans-anethole is excreted in breast milk. In pregnant mice an aqueous seed extract caused dose-dependent teratogenic effects.

Estragole is the other flag. A safety assessment of fennel teas found a low priority for risk management in adults, especially at one cup a day, and a higher priority for children, which falls if use is limited to 1 or 2 weeks. Infusions of whole fruits contained about three times less estragole than fine-cut material.

Medicines it can interact with

The European monograph lists no interactions reported, and we could not find a controlled interaction study of fennel with any medicine class. The oil has been described in laboratory work as acting on intestinal smooth muscle, so any effect alongside drugs that act on gut motility is untested rather than ruled out. The catalog’s own drug rules for fennel products are listed automatically on this page.

The interaction rules the quiz applies to fennel

These are the medicines the quiz pairs with a caution or an exclusion for this herb, taken from published interaction references:

ciprofloxacin (taken apart)
alprazolam (flagged to check)
amlodipine (flagged to check)
antiplatelets (flagged to check)
apixaban (flagged to check)
aspirin-prescription (flagged to check)
atorvastatin (flagged to check)
blood thinner (flagged to check)
blood thinners (flagged to check)
buspirone (flagged to check)
clarithromycin (flagged to check)
clopidogrel (flagged to check)
conjugated equine estrogens (flagged to check)
conjugated estrogens (flagged to check)
cyclosporine (flagged to check)
dabigatran (flagged to check)
dalteparin (flagged to check)
diltiazem (flagged to check)
and 35 more

Where fennel turns up in the catalog

Fennel appears on the labels below, alone or inside a blend; each product page gives the printed amount, the evidence for that product and the review picture.

11 more entries list it; the full catalog is grouped by the job each product does.

Which product, for your symptoms?

The quiz weighs your symptoms and medicines against every product researched here, fennel products included, and shows its working.

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Questions people ask

Does fennel help infant colic?