NutriDex

The Supplement Research Compendium
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Fennel

A crisp, anise-scented bulb best evidenced for easing menstrual and menopausal symptoms.

Moderate evidence 🥦Vegetables

✚ Updated · How we grade evidence

Evidence tier
Moderate
Research weight
Citations
9 verified / 9
Classification
Vegetables
❝
What the evidence says. Several controlled trials; effects real but modest or context-dependent.

Nutrition per serving 1 cup sliced, raw (87 g)

87gSERVING
  • Sugars 3.4 g4%
  • Fibre 2.7 g3%
  • Other carbs 0.2 g0%
  • Protein 1.1 g1%
  • Other 79.6 g91%
What's in one serving, by weight — average composition (USDA).
Vitamin C12%Fiber10%Potassium8%Folate6%Vitamin A5%Vitamin K46%Vitamin B62%Manganese7%
One serving as % of the adult daily requirement (FDA Daily Values). The bold outer ring = 100% of a day's needs.
27 kcal1.1 g protein2.7 g fiber3.4 g sugar
NutrientPer serving% daily value
Vitamin C10 mg12%
Fiber2.7 g10%
Potassium360 mg8%
Folate23 µg6%
Vitamin A42 µg5%
Vitamin K55 µg46%
Vitamin B60.04 mg2%
Manganese0.17 mg7%
Copper0.06 mg7%
Vitamin E0.5 mg3%
Magnesium15 mg4%
Calcium43 mg3%

Composition data: USDA FoodData Central ↗

What is Fennel?

Fennel is a vegetable used for reduces primary dysmenorrhea (menstrual) pain. NutriDex grades the human evidence as Moderate. Fennel bulb is a low-calorie, hydrating vegetable supplying potassium, vitamin C, vitamin K and the phytoestrogenic essential-oil compound trans-anethole. Its strongest human evidence is in gynecologic symptom relief: meta-analyses of randomized trials show fennel meaningfully reduces primary dysmenorrhea pain (comparable to NSAIDs) and improves menopausal symptom scores, though most trials are small, Iran-based and at risk of bias. Cardiometabolic and weight effects remain unproven in controlled trials.

Purported Benefits

✓Reduces primary dysmenorrhea (menstrual) pain
✓Improves menopausal symptom scores
✓May reduce infant colic crying time
✓Hydrating, low-calorie source of potassium and vitamin K
✓Provides vitamin C and antioxidant polyphenols

Dosing & Compounds

Typical Dose
Standard serving: 1 cup sliced, raw (87 g). Eat whole (with skin where edible); favour whole fruit over juice.
Active Compounds
trans-anetholeestragolefenchonelimonenealpha-pinenequercetinrosmarinic acid

Safety & Cautions

Concentrated fennel essential oil/extract carries higher exposure to estragole (a rodent hepatocarcinogen) than culinary amounts; supplements should be avoided in pregnancy and in estrogen-sensitive conditions given anethole's mild phytoestrogenic activity. Rare IgE allergy occurs, often cross-reacting with celery, carrot and mugwort/birch pollen. Vitamin K content is modest but relevant for those on warfarin. Culinary bulb amounts are considered safe. Educational only — always check with your doctor or pharmacist before combining Fennel with any medicine.

Key Studies

Systematic review & meta-analysis of RCTs Lee 2020 (Nutrients) ✓ Full text
Across 12 RCTs, fennel was as effective as conventional drugs for dysmenorrhea (n=502, SMD 0.07, 95% CI -0.08 to 0.21) and superior to placebo for pain reduction (n=468, SMD -3.27, 95% CI -5.28 to -1.26, p=0.001).
Systematic review & meta-analysis Nasiri Lari 2021 (J Complement Integr Med) ✓ PubMed
Pooling 12 trials, fennel significantly reduced primary dysmenorrhea pain versus placebo (SMD -0.632) and was comparable to mefenamic acid.
Systematic review & meta-analysis of RCTs Lee 2021 (Complement Ther Clin Pract) ✓ PubMed
Two placebo-controlled RCTs (n=145) showed fennel significantly improved menopausal symptom scores (SMD -1.32, 95% CI -1.76 to -0.87, p<0.00001).
Systematic review protocol of RCTs Ghodsi 2018 (PMC5895370, protocol) ✓ Full text
Registered protocol synthesizing RCTs of fennel for menopausal symptoms, establishing the methodological basis for subsequent meta-analyses.
Double-blind randomized placebo-controlled trial Yazdani 2017 / J Menopausal Med (Saghafi 2017) ✓ Full text
In 47 overweight postmenopausal women over 12 weeks, fennel (soft capsule) showed no significant effect on body weight, BMI, waist/hip circumference or fat distribution versus placebo.
Randomized placebo-controlled trial Alexandrovich 2003 (Altern Ther Health Med) ✓ PubMed
Fennel seed oil emulsion eliminated infantile colic in 65% of treated infants versus 23.7% on placebo (p<0.01) by reducing crying time.
Narrative pharmacological review Rather 2016 / Badgujar 2014 review ✓ PubMed
Reviews Foeniculum vulgare phytochemistry (trans-anethole, fenchone, estragole) and pharmacology, summarizing antioxidant, antispasmodic and estrogenic activities underpinning clinical use.
Review 2006 ✓ PubMed
Reference monograph on fennel, covering its safety profile including use during breastfeeding.
Review 2006 ✓ PubMed
Goat's Rue
9 sources cited · 9 verified Search all studies on PubMed ↗

Common questions about Fennel

What is Fennel used for?

Fennel is most often taken for Reduces primary dysmenorrhea (menstrual) pain, Improves menopausal symptom scores, May reduce infant colic crying time, Hydrating, low-calorie source of potassium and vitamin K. A crisp, anise-scented bulb best evidenced for easing menstrual and menopausal symptoms.

Does Fennel work — what does the evidence say?

Moderate evidence. Several controlled trials; effects real but modest or context-dependent. Fennel bulb is a low-calorie, hydrating vegetable supplying potassium, vitamin C, vitamin K and the phytoestrogenic essential-oil compound trans-anethole. Its strongest human evidence is in gynecologic symptom relief: meta-analyses of randomized trials show fennel meaningfully reduces primary dysmenorrhea pain (comparable to NSAIDs) and improves menopausal symptom scores, though most trials are small, Iran-based and at risk of bias. Cardiometabolic and weight effects remain unproven in controlled trials.

What is the typical dose of Fennel?

Standard serving: 1 cup sliced, raw (87 g). Eat whole (with skin where edible); favour whole fruit over juice.

Is Fennel safe? Any cautions or side effects?

Concentrated fennel essential oil/extract carries higher exposure to estragole (a rodent hepatocarcinogen) than culinary amounts; supplements should be avoided in pregnancy and in estrogen-sensitive conditions given anethole's mild phytoestrogenic activity. Rare IgE allergy occurs, often cross-reacting with celery, carrot and mugwort/birch pollen. Vitamin K content is modest but relevant for those on warfarin. Culinary bulb amounts are considered safe.

How many studies support Fennel?

NutriDex cites 9 sources for Fennel, graded "Moderate".

Cite this page
APA

Peh, D. (2026). Fennel: Benefits, Dosage, Side Effects & Evidence. NutriDex — The Supplement Research Compendium. Retrieved 16 Sept 2026, from https://nutridex.info/s/fennel

BibTeX
@misc{nutridex_fennel,
  author       = {Peh, Daryl},
  title        = {Fennel: Benefits, Dosage, Side Effects \& Evidence},
  year         = {2026},
  howpublished = {NutriDex --- The Supplement Research Compendium},
  url          = {https://nutridex.info/s/fennel},
  note         = {Reviewed by Dr Daryl Peh, MBBS Singapore, MMed FM. Accessed 2026-09-16}
}

For medical claims, citing the underlying primary studies linked above is preferred. NutriDex is an educational reference, not medical advice.

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