Fennel
Also called Foeniculum vulgare, fennel seed, fennel fruit, sweet fennel, bitter fennel, fennel seed oil.
Best grade C across 5 graded outcomes Botanical Last checked
The short answer
From 12 sourcesFennel seed is a traditional remedy for bloating, menstrual cramps and coughs. Small trials report less menstrual pain and fewer menopausal symptoms, and one infant colic trial was positive, but study quality is low. EU regulators do not recommend it in pregnancy, breastfeeding or under age 4, citing limited safety data and estragole.
Every graded outcome on this page
5 rows · line = participants- CGrade CMenstrual cramp pain (primary dysmenorrhoea)Menstrual crampsn 502
- CGrade CMenopausal symptomsMenopausen 145
- CGrade CInfant colic (crying under 9 hours a week)Infant colicn 121
- CGrade CMenopause Rating Scale scoreMenopausen 90
- CGrade CMenopause-specific quality of life (hot flushes, sweats, mood)Menopausen 50
- 2 more graded outcomes, in the evidence chapter
Key facts
- What it is
- The dried fruit (seed) of sweet or bitter fennel; its oil is rich in trans-anethole and also contains estragole18
- Top studied outcome
- Menstrual cramp pain: similar to standard pain drugs across 7 small trials (502 women), grade C3
- Traditional uses (EU)
- Mild spasmodic digestive complaints including bloating, minor menstrual cramps, and cough with a cold1
- Estragole limits
- EU limits estragole to under 0.05 mg a day in pregnancy and breastfeeding and under 1.0 mcg/kg in children under 121
- Children
- Not recommended under 4 years in the EU monograph because of a lack of adequate data1
- Allergy
- Avoid with allergy to fennel, anethole, mugwort pollen or Apiaceae plants such as anise, caraway, celery, coriander and dill1
What it is
Fennel (Foeniculum vulgare) is a Mediterranean herb whose dried fruits, called seeds, are used as a tea, extract or oil.
Forms, side by side
3 forms named in our sources. The rest show what our data holds, and say plainly where it holds nothing yet.
Fennel forms compared
3 forms| 3 forms | Seed tea (infusion) | Capsules and extracts | Seed oil |
|---|---|---|---|
| Absorption in people | No human absorption data in our sources.1 | No human absorption data in our sources.5 | No human absorption data in our sources.7 |
| GI tolerance | Allergic skin or breathing reactions can occur; frequency unknown.1 | No serious side effects in an 8-week trial of 200 mg/day.5 | Health Canada's bitter fennel monograph lists 0.2 ml of essential oil a day for adults only.7 |
| Studied for | EU traditional use: 1.5 g in 250 ml boiling water, three times daily, for adults and adolescents, up to 2 weeks | Menopausal symptoms and menstrual cramps | Infant colic (emulsion, one trial) |
- Fennel seed tea (infusion)
- Capsules and extracts
- Fennel seed oil
What the human research says
Human trials only, one row per outcome. The form line shows what each trial actually tested. Grades follow our evidence-grading policy.
Trial map
5 graded outcomes, largest study first5 graded outcomes: 4 improved, 1 no effect. The largest, a 2020 meta-analysis of 502 people on menstrual cramp pain (primary dysmenorrhoea), found an improvement.
1Menstrual cramp pain (primary dysmenorrhoea)
Improved · Grade C · Meta-analysis, 502 people, 2020
Women with primary dysmenorrhoea in 12 randomized trials
Dose, result and source| Outcome | Found | People | Study | Who was studied |
|---|---|---|---|---|
| Menstrual cramp pain (primary dysmenorrhoea) | Improved | 502 | Grade C · Meta-analysis, 2020 | Women with primary dysmenorrhoea in 12 randomized trials |
| Menopausal symptoms | Improved | 145 | Grade C · Meta-analysis, 2021 | Menopausal women in 2 placebo-controlled trials (7 trials reviewed) |
| Infant colic (crying under 9 hours a week) | Improved | 121 | Grade C · RCT, 2003 | Infants aged 2 to 12 weeks with colic (125 randomized) |
| Menopause Rating Scale score | Improved | 90 | Grade C · RCT, 2017 | Postmenopausal women aged 45 to 60 (Tehran, Iran) |
| Menopause-specific quality of life (hot flushes, sweats, mood) | No effect | 50 | Grade C · RCT, 2018 | Postmenopausal women (Mashhad, Iran) |
Every graded row
5 rowsShowing 5 of 5 outcomes. Human trials only.
CGrade CMenstrual cramp pain (primary dysmenorrhoea)Menstrual crampsSMD 0.07 vs drugsMeta-analysis · 12 studies
n 502 · 2020
Improved In 7 trials (n = 502) fennel relieved pain about as well as conventional drugs (SMD 0.07). Against placebo (n = 468) it reduced pain, but with extreme heterogeneity (I2 = 98%). Publication bias from many small positive studies was likely; only 3 trials assessed adverse events.
- Design
- Meta-analysis, 12 studies, n = 502, 2020
- Population
- Women with primary dysmenorrhoea in 12 randomized trials
- Form
- Fennel preparations (varied)
- Dose
- Varied across trials
- Duration
- Varied
- Source
- Reference 3 · PubMed 33182553 (opens PubMed)
CGrade CMenopausal symptomsMenopauseSMD -1.32Meta-analysis · 2 studies
n 145 · 2021
Improved Pooled results of 2 placebo-controlled trials favoured fennel for menopausal symptoms (SMD -1.32). Other trials did not show benefits for sexual function, quality of life or mood; included trials had concerning risks of bias.
- Design
- Meta-analysis, 2 studies, n = 145, 2021
- Population
- Menopausal women in 2 placebo-controlled trials (7 trials reviewed)
- Form
- Fennel preparations
- Dose
- Varied across trials
- Duration
- Varied
- Source
- Reference 4 · PubMed 33725577 (opens PubMed)
CGrade CInfant colic (crying under 9 hours a week)Infant colicImprovedRCT
n 121 · 2003
Improved Colic resolved in 65% (40/62) on fennel oil vs 23.7% (14/59) on placebo (absolute risk reduction 41%, NNT 2). No side effects were reported during the trial.
- Design
- RCT, n = 121, 2003
- Population
- Infants aged 2 to 12 weeks with colic (125 randomized)
- Form
- Fennel seed oil emulsion vs placebo
- Dose
- Not stated in the abstract
- Duration
- Not stated in the abstract
- Source
- Reference 2 · PubMed 12868253 (opens PubMed)
CGrade CMenopause Rating Scale scoreMenopauseImprovedRCT
n 90 · 2017
Improved Menopause Rating Scale scores fell significantly more than with placebo at 4, 8 and 10 weeks (P < 0.001); no serious side effects were reported.
- Design
- RCT, n = 90, 2017
- Population
- Postmenopausal women aged 45 to 60 (Tehran, Iran)
- Form
- Fennel soft capsules
- Dose
- 100 mg capsule twice daily (200 mg/day)
- Duration
- 8 weeks, plus 2 weeks follow-up
- Source
- Reference 5 · PubMed 28509813 (opens PubMed)
CGrade CMenopause-specific quality of life (hot flushes, sweats, mood)MenopauseNo effectRCT
n 50 · 2018
No effect Both fennel and placebo groups improved; there was no difference between groups on any menopausal symptom except one urinary item. The authors attribute the null result to a high placebo response.
- Design
- RCT, n = 50, 2018
- Population
- Postmenopausal women (Mashhad, Iran)
- Form
- Oral fennel soft capsules
- Dose
- Not stated in the abstract
- Duration
- 3 months
- Source
- Reference 6 · PubMed 29755029 (opens PubMed)
What the numbers add up to
Each point is worked out from the data and the sources numbered on this page, with the arithmetic shown under it. It adds no new data and is not medical advice.
Studied doses
Doses used in research, shown against the official limits. They describe the studies, not a recommendation for you.
Studied doses in research, not advice. These are amounts used in research, not personal advice. Your clinician or pharmacist can say what fits you.
Doses studied in human trials
Interactions and safety
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
What Fennel meets
1 cited rowMedicines 1
Supplements and foods 0
No supplement rows in our sources.
- Reference summary
Choose a medicine or supplement above to read its cited rows here.
Also cited:
Heart and blood pressure medicines cleared by CYP3A4
ReviewReference summary
Heart and blood pressure medicines cleared by CYP3A4, for example amlodipine, nifedipine, verapamil, eplerenone, spironolactone: A 2025 review notes that fennel inhibits the liver enzyme CYP3A4 and could raise levels of calcium channel blockers, some diuretics and some beta blockers that it clears. The authors say most data come from lab and animal studies, not people.
Source 10, Pharmaceuticals (Basel) (2025)
Interactions
1 agent| Agent | What the source says | Evidence |
|---|---|---|
| Medicines1 | ||
| Heart and blood pressure medicines cleared by CYP3A4e.g. amlodipine, nifedipine, verapamil, eplerenone, spironolactone | A 2025 review notes that fennel inhibits the liver enzyme CYP3A4 and could raise levels of calcium channel blockers, some diuretics and some beta blockers that it clears. The authors say most data come from lab and animal studies, not people.10 | Review |
Check with what you take
Kept on this device onlyAdd what you take. We list every interaction our evidence profiles cite between Fennel and your picks, and between your picks.
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Add a supplement or medicine you take to check it against Fennel.
Starting from one medicine? The interaction checker rates how serious each pair is, on a curated list of 19 entries for 11 medicines. This cabinet has no severity rating: it lists every interaction row our supplement pages cite.
Who should be careful
5 groups- Pregnancy
- Safety in pregnancy has not been established and the EU monograph does not recommend use. It cites a mouse study in which an aqueous fennel seed extract given during pregnancy caused dose-dependent birth defects, and notes that adequate reproductive toxicity tests have not been done. Health Canada advises asking a health care practitioner before use in pregnancy.19
- Breastfeeding
- The EU monograph does not recommend use while breastfeeding, and trans-anethole passes into breast milk. LactMed says the smaller amounts in milk are likely not harmful at usual maternal doses, since fennel has been used in infants for colic, and notes some sources limit use to 2 weeks. Heavy maternal use (over 2 liters a day) of a mixed herbal tea containing fennel and anise appeared to cause toxicity in two breastfed newborns, who recovered after it was stopped.18
- Children under 4
- Not recommended under 4 years because of a lack of adequate data and the estragole content; for ages 4 to 12 the EU limits estragole intake and use to under a week. LactMed notes fennel has been used alone and with other herbs in infants for colic, but the only fennel-alone infant trial we found dates from 2003.182
- Apiaceae, anethole or mugwort allergy
- Contraindicated with allergy to fennel, anethole, mugwort pollen, or related plants such as anise, caraway, celery, coriander and dill. LactMed adds carrots to the cross-allergy list for mothers and infants, and notes that fennel can cause skin and breathing allergic reactions, including sun sensitivity (photosensitivity).18
Safety
4 notesAllergy and estragole exposure are the main concerns.
- Allergic reactions
- Skin and respiratory allergic reactions may occur; LactMed also mentions photosensitivity.18
- Estragole
- Estragole is a genotoxic carcinogen in rodents; EU regulators advise keeping exposure as low as practical.1
- Interactions
- No drug interactions are reported in the EU monograph.1
- Galactagogue mixtures
- LactMed reports diarrhoea and an enlarged liver in a woman using fennel, fenugreek and goat's rue together, and raised liver enzymes with a tea containing fennel.8
How to read the label
What to check on the Supplement Facts panel.
How to read the label
3 checksLabel dose vs clinical dose
Sweet vs bitter fennel
Short courses
Regulators frame fennel as short-term use: up to 2 weeks for adults and under a week for children aged 4 to 12.1
Frequently asked questions
Short answers to common questions; the numbers link to the sources below.
Common questions
8 answersDoes fennel help menstrual cramps?
Probably a little, but the trials are small. A 2021 meta-analysis found less pain than placebo (SMD −0.63, 7 trials) and no difference from mefenamic acid; a 2020 analysis found it about as effective as standard pain drugs in 502 women, with possible publication bias. A 2026 review of related herbs reported a significant subgroup result for fennel and dill seed against mefenamic acid or ibuprofen. We grade it C.12311
Does fennel increase breast-milk supply?
Not clearly. LactMed reports that two small studies found more milk volume, milk fat or infant weight gain, but no rise in prolactin with fennel; most other studies tested multi-herb teas, so fennel alone cannot be credited. It is a common traditional galactogogue, and the EU monograph does not recommend it while breastfeeding.81
Does fennel help menopause symptoms?
Can fennel affect heart or blood pressure medicines?
Is fennel tea safe for babies with colic?
Who should avoid fennel?
People allergic to fennel, anethole, mugwort pollen or related plants such as anise, celery, coriander, caraway and dill.1
Is fennel safe to use long term?
Long-term safety has not been studied. The EU monograph limits adult use to 2 weeks, and Health Canada advises asking a practitioner for use beyond 2 weeks (1 week for children aged 4 to 11). EU regulators also advise keeping estragole exposure as low as practical because it causes cancer in rodents.19
Sources
12 sources: trial abstracts, NIH fact sheets and reference databases. Numbers in the text link here.
Sources cited on this page
12 sources- 1European Union herbal monograph on Foeniculum vulgare Miller subsp. vulgare var. dulce (Mill.) Batt. & Trab., fructus (Revision 1, EMEA/HMPC/372839/2016)Guideline European Medicines Agency (HMPC), 2024 · ema.europa.eu
- 2The effect of fennel (Foeniculum Vulgare) seed oil emulsion in infantile colic: a randomized, placebo-controlled study.RCT Altern Ther Health Med, 2003 · PMID 12868253
- 3Fennel for Reducing Pain in Primary Dysmenorrhea: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.Meta-analysis Nutrients, 2020 · PMID 33182553
- 4Fennel (Foeniculum vulgare Miller) for the management of menopausal women's health: A systematic review and meta-analysis.Meta-analysis Complement Ther Clin Pract, 2021 · PMID 33725577
- 5Effect of Foeniculum vulgare Mill. (fennel) on menopausal symptoms in postmenopausal women: a randomized, triple-blind, placebo-controlled trial.RCT Menopause, 2017 · PMID 28509813
- 6A double-blind, placebo-controlled trial of Fennel (Foeniculum vulgare) on menopausal symptoms: A high placebo response.RCT J Turk Ger Gynecol Assoc, 2018 · PMID 29755029
- 7Natural health product monograph: Bitter Fennel - Foeniculum vulgare (November 29, 2024)Guideline Health Canada, 2024 · webprod.hc-sc.gc.ca
- 8Fennel. Drugs and Lactation Database (LactMed).Database NICHD, 2026 · PMID 30000852
- 9Natural health product monograph: Sweet Fennel - Foeniculum vulgare (November 29, 2024)Guideline Health Canada, 2024 · webprod.hc-sc.gc.ca
- 10Cardiovascular Effects, Phytochemistry, Drug Interactions, and Safety Profile of Foeniculum vulgare Mill. (Fennel): A Comprehensive Review.Review Pharmaceuticals (Basel), 2025 · PMID 41305003
- 11Efficacy of herbaceous Apiaceae plants in primary dysmenorrhea: A systematic review and meta-analysis of RCTs.Meta-analysis Ann Pharm Fr, 2026 · PMID 41653970
- 12Effect of fennel on primary dysmenorrhea: a systematic review and meta-analysis.Meta-analysis J Complement Integr Med, 2021 · PMID 34187122
What changed
Every dated change to this page: what changed, who made it and why.
Change log
4 entries| Date | Change | Who and why |
|---|---|---|
| all | Split the pregnancy and breastfeeding note and added LactMed's infant-safety points (amounts in milk, 2-week limit, carrot and Apiaceae cross-allergy, sun sensitivity); added three FAQ items (milk supply, long-term use, interactions), page questions and a gut goal link; updated the menstrual-cramp FAQ with a 2021 fennel meta-analysis and a 2026 Apiaceae meta-analysis (neither gives a participant total in the abstract, so neither is a graded row). PubMed search for fennel meta-analyses and RCTs 2021–2026 found no newer fennel-only pooled analysis with a participant total; 2025 infertility trials were not added. Interactions checked in LactMed, the EU monograph and Health Canada: none beyond the CYP3A4 review; no LiverTox entry. | Writer: Kymata Health EditorialTrigger: A–Z audit against docs/supplements/AUDIT-STANDARD.md |
| Interactions | Added 1 interaction entry (Heart and blood pressure medicines cleared by CYP3A4) from peer-reviewed reviews; each PubMed abstract or full text was read for the cited statement. | Writer: Kymata Health EditorialTrigger: Update |
| all | Initial editorial evidence review (first draft). Every PMID checked against NCBI E-utilities esummary (title and year) and each cited abstract read; numbers taken from the abstracts. No retractions or errata linked to the cited PMIDs. Funding: the 2020 dysmenorrhoea meta-analysis was funded by the Korea Institute of Oriental Medicine; no industry funding is stated in the other abstracts. Safety, interaction and pregnancy text come only from the EMA monograph (Revision 1, 31 January 2024), Health Canada's bitter fennel monograph and LactMed. No product links. | Writer: Kymata Health EditorialTrigger: new page |
| evidence and safety | Adversarial review: disclosed that Barij Essence supplied the capsules for the 2018 menopause trial (Mashhad University grant) and that a 2017 trial co-author lists a Barij research-centre affiliation; added the EU monograph's mouse teratogenicity finding to the pregnancy advice. | Writer: Kymata Health EditorialTrigger: adversarial review |
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