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Last verified: 17 days ago

Fennel Seed

Also known as: Foeniculum vulgare, sweet fennel, fennel seed extract, fennel seed oil, FEO

Evidence under review. — Not yet rated

Herbal seed with early evidence for easing colic, menopause symptoms, and period pain.

  • What it does

    Fennel seed comes from the Foeniculum vulgare plant and has been used in traditional medicine for digestive and hormonal complaints. Clinical trials suggest it may reduce crying time in colicky...

  • Evidence quality

    Evidence base hasn't been formally rated yet. See research below.

  • Clinical dose

    400-2000 mg daily (varies by condition and form)

  • Found in

    zuPoo, Perfect Form Herbal Digestive Supplement, Gastro-Fiber® and 1 more

See full breakdown ↓ Methodology →

What the Science Says

Fennel seed comes from the Foeniculum vulgare plant and has been used in traditional medicine for digestive and hormonal complaints. Clinical trials suggest it may reduce crying time in colicky infants, ease menopausal symptoms like hot flashes, and help manage painful periods — with effects seen in as little as 2–8 weeks. Its active compounds, including trans-anethole, have mild phytoestrogenic and antispasmodic properties that may explain these effects.

What It Doesn't Do

Not proven to boost sexual desire. Won't meaningfully raise estrogen levels in postmenopausal women. No solid evidence it promotes weight loss. Not a replacement for standard pain medications like ibuprofen. The bone-regeneration research is only in lab cells — don't expect it to treat osteoporosis.

Evidence-Based Benefits

Fennel seed oil emulsion reduced colic symptoms in 65% of infants vs. 24% on placebo.

Moderate Evidence

Effective at: Fennel seed oil emulsion (dose not specified in mg)

Supporting studies (click to view on PubMed):

PMID 12868253

Taking 2 g of fennel seed powder daily for 8 weeks significantly reduced menopausal symptom scores.

Weak Evidence

Effective at: 2 g/day powder for 8 weeks

Supporting studies (click to view on PubMed):

PMID 33110044

Fennel seed performs comparably to standard treatments like mefenamic acid for reducing primary dysmenorrhea pain.

Weak Evidence

Effective at: No established dose from provided studies

Supporting studies (click to view on PubMed):

PMID 41653970

Fennel seed extract capsules reduced knee pain and disability scores in women with osteoarthritis after 2 weeks.

Weak Evidence

Effective at: 800 mg/day dried extract for 2 weeks

Supporting studies (click to view on PubMed):

PMID 32835919

Absorption & Bioavailability

Unknown — no pharmacokinetic studies were provided. Oil-based emulsion forms were used in the colic trial; powder capsules in women's health trials. Form likely affects absorption.

Red Flags to Watch For

  • Fennel contains estragol, a compound with suspected genotoxic potential at high doses — safety as a supplement (not just a flavoring) has not been fully established
  • Most clinical trials are small (under 80 participants) and short-term; long-term safety data is lacking
  • The PCOS/oligomenorrhea trial combined fennel with dry cupping, making it impossible to isolate fennel's effect alone
  • Phytoestrogenic activity means people with hormone-sensitive conditions (e.g., estrogen-receptor-positive cancers) should consult a doctor before use
  • Animal studies (piglets) showed fennel oil did not improve growth performance and was actually avoided by animals when given a choice

Products Containing Fennel Seed

See how Fennel Seed is used in these analyzed products:

zuPoo

Supplement

Misleading

Perfect Form Herbal Digestive Supplement

Supplement

Mostly Legit

Gastro-Fiber®

Supplement

Mostly Legit

Inno Cleanse™

Supplement

Misleading
View all product reviews →

Frequently Asked Questions

What does Fennel Seed do?

Herbal seed with early evidence for easing colic, menopause symptoms, and period pain.

What is the effective dose of Fennel Seed?

400-2000 mg daily (varies by condition and form)

Is Fennel Seed safe?

Fennel contains estragol, a compound with suspected genotoxic potential at high doses — safety as a supplement (not just a flavoring) has not been fully established

What doesn't Fennel Seed do?

Not proven to boost sexual desire.

Research Sources

  • PubMed
  • NIH DSLD

This information is for educational purposes only and is not medical advice. Always consult a healthcare professional before starting any supplement regimen. Last updated: 2026-05-25