What is fennel tea good for?

Strong = multiple human trials or a meta-analysis. Moderate = a few small trials. Preliminary = early, traditional or animal data.

1. 1

   Relieves infant colic (as a measured extract)

   Moderate evidence

   Three placebo-controlled trials support fennel for colic. A 0.1% fennel seed oil emulsion given to 125 colicky infants for one week eliminated colic in 65% versus 23.7% on placebo. A standardized chamomile, fennel and lemon balm extract reduced crying time in 85.4% of 93 breastfed infants versus 48.9% on placebo over one week. An earlier blended herbal tea including fennel resolved colic in 57% versus 26%. These used measured extracts, not home-brewed tea, and European regulators advise against fennel tea in children under four because of estragole.

   Key evidenceAlexandrovich et al., Altern Ther Health Med 2003: 125-infant RCT, 65% vs 24% colic-free

2. 2

   Eases period cramps

   Moderate evidence

   In a 60-woman trial, 30 mg of fennel extract every six hours at the start of menstruation relieved primary dysmenorrhea about as well as mefenamic acid 250 mg, though fennel worked slightly less at the two-hour mark. A later placebo-controlled trial found fennel 30 mg every four hours reduced pain intensity significantly. The 2016 Cochrane review of dietary supplements for dysmenorrhea judged the fennel evidence low quality because the trials were small and short, but the direction of effect was consistently positive.

   Key evidenceNamavar Jahromi et al., Int J Gynaecol Obstet 2003: fennel vs mefenamic acid, 60 women

3. 3

   Reduces menopause symptoms

   Moderate evidence

   A triple-blind trial randomized 90 postmenopausal women to fennel 100 mg soft capsules twice daily or placebo for eight weeks. Menopause Rating Scale scores fell significantly more with fennel at four and eight weeks, with improvements in hot flashes, sleep and mood domains, and no serious adverse effects. The plausible mechanism is anethole and related phytoestrogens. One trial is not a consensus, and the dose was a standardized capsule rather than tea.

   Key evidenceRahimikian et al., Menopause 2017: 90-woman triple-blind RCT, 8 weeks

4. 4

   Eases gas and bloating

   Preliminary evidence

   Fennel's carminative reputation rests on tradition and mechanism rather than trials of the tea. Anethole and fenchone relax intestinal smooth muscle and reduce spasm in animal and tissue studies, which would allow trapped gas to pass. The only relevant human trial combined fennel essential oil with curcumin in 121 people with irritable bowel syndrome for 30 days, with a significant drop in symptom scores and bloating versus placebo, but curcumin confounds the result. Most people notice relief within 20 to 30 minutes of a cup after a heavy meal, and that is a reasonable thing to try.

   Key evidencePortincasa et al., J Gastrointestin Liver Dis 2016: curcumin plus fennel oil in IBS, 121 patients

5. 5

   Helps with mild constipation

   Preliminary evidence

   A randomized trial of a herbal tea containing fennel, anise, elderflower and senna in 20 people with chronic constipation increased bowel movements and reduced colonic transit time over five days. Senna is a proven laxative, so the trial cannot credit fennel. On its own, fennel's muscle-relaxing effect is more antispasmodic than laxative, so it may ease the cramping of constipation without doing much to speed things up.

6. 6

   Boosts breast-milk supply

   Preliminary evidence

   Fennel is a traditional galactagogue in Europe, the Middle East and South Asia, and small studies of multi-herb lactation teas have reported modest increases in milk volume. No trial has isolated fennel, and the reviews that exist rate the evidence as poor. Anethole is estrogenic, and in one Turkish case series, infant girls given fennel tea directly developed early breast development that resolved when the tea was stopped, so it should not be given to babies.

   Key evidenceTurkyilmaz et al., J Pediatr Surg 2008: premature thelarche in infants given fennel tea

7. 7

   Antioxidant and antimicrobial activity

   Preliminary evidence

   Fennel seed is rich in rosmarinic acid, quercetin and chlorogenic acid, and its extracts inhibit a range of bacteria and fungi in culture, including Helicobacter pylori and Candida albicans. Animal studies show liver-protective and anti-inflammatory effects at doses far above what a cup provides. These findings justify research interest but say nothing yet about what fennel tea does in a person.

Is fennel tea good for you?

• Yes, for most adults: one to three cups a day is a safe, pleasant way to ease gas and bloating after meals, with a plausible mechanism and good tolerability.
• The best-proven uses are measured extracts for infant colic, period pain and menopause symptoms; the tea gives a lower, less predictable dose of the same oils.
• Go easy if you have a hormone-sensitive condition such as estrogen-receptor-positive breast cancer, endometriosis or fibroids, since fennel compounds act weakly like estrogen.
• Do not give fennel tea to infants or children under four, and avoid medicinal amounts in pregnancy; culinary fennel is fine.
• People allergic to celery, carrot, dill or mugwort can react to fennel, which is in the same plant family.

• Crush the seeds with the back of a spoon just before brewing; whole seeds release little anethole.
• Keep the cup covered while steeping, since the active oils evaporate with the steam.
• Fresh seeds are sweet; stale ones taste flat and bitter, so buy small amounts.

Frequently asked questions

1. Alexandrovich I, Rakovitskaya O, Kolmo E, Sidorova T, Shushunov S. The effect of fennel (Foeniculum vulgare) seed oil emulsion in infantile colic: a randomized, placebo-controlled study. Alternative Therapies in Health and Medicine (2003)
2. Savino F, Cresi F, Castagno E, Silvestro L, Oggero R. A randomized double-blind placebo-controlled trial of a standardized extract of Matricariae recutita, Foeniculum vulgare and Melissa officinalis (ColiMil) in the treatment of breastfed colicky infants. Phytotherapy Research (2005)
3. Namavar Jahromi B, Tartifizadeh A, Khabnadideh S. Comparison of fennel and mefenamic acid for the treatment of primary dysmenorrhea. International Journal of Gynaecology and Obstetrics (2003)
4. Omidvar S, Esmailzadeh S, Baradaran M, Basirat Z. Effect of fennel on pain intensity in dysmenorrhoea: a placebo-controlled trial. Ayu (2012)
5. Pattanittum P, Kunyanone N, Brown J, et al.. Dietary supplements for dysmenorrhoea. Cochrane Database of Systematic Reviews (2016)
6. Rahimikian F, Rahimi R, Golzareh P, Bekhradi R, Mehran A. Effect of Foeniculum vulgare Mill. (fennel) on menopausal symptoms in postmenopausal women: a randomized, triple-blind, placebo-controlled trial. Menopause (2017)
7. Portincasa P, Bonfrate L, Scribano ML, et al.. Curcumin and fennel essential oil improve symptoms and quality of life in patients with irritable bowel syndrome. Journal of Gastrointestinal and Liver Diseases (2016)
8. Turkyilmaz Z, Karabulut R, Sonmez K, Can Basaklar A. A striking and frequent cause of premature thelarche: Foeniculum vulgare. Journal of Pediatric Surgery (2008)
9. Zhu M, Wong PY, Li RC. Effect of oral administration of fennel (Foeniculum vulgare) on ciprofloxacin absorption and disposition in the rat. Journal of Pharmacy and Pharmacology (1999)
10. Badgujar SB, Patel VV, Bandivdekar AH. Foeniculum vulgare Mill: a review of its botany, phytochemistry, pharmacology, contemporary application, and toxicology. BioMed Research International (2014)
11. Committee on Herbal Medicinal Products (HMPC). Community herbal monograph on Foeniculum vulgare Miller subsp. vulgare var. vulgare, fructus. European Medicines Agency (2007)