Anise seed: one striking trial, never repeated

The best evidence for anise seed is a single trial. In Iran, 107 adults with functional dyspepsia, the fullness and discomfort after meals that has no visible cause, took 3 g of anise powder after each meal for 4 weeks. Their symptom score fell from 10.6 to 2.44, while the placebo group went from 10.96 to 13.05. The trial ran at one center with unequal groups of 47 and 60, and a drop that large is hard to accept from one study. A Cochrane review rated the finding low certainty for that reason: one trial of 107 people, never repeated. The dose was powder taken three times a day, 9 g in all, which is a supplement regimen. A teaspoon of whole seed weighs 2.1 g. The European Medicines Agency advises against preparations with more than 5 g of seed for longer than two weeks without medical advice.

The numbers, per 3.5 oz (100 g)

How much is actually in it

• USDA lists anise seed at 337 calories, 17.6 g protein, 14.6 g fiber and 37 mg iron per 3.5 oz (100 g), but a teaspoon weighs only 2.1 g, so it adds about 0.8 mg iron and 7 calories. — US food composition Evidence E source
  Per 100 g: 337 calories, protein 17.6 g, fat 15.9 g, fiber 14.6 g, calcium 646 mg, iron 36.96 mg, potassium 1441 mg; 1 tsp whole = 2.1 g
• UK food tables give anise seeds 37 mg iron, 650 mg calcium and 17.6 g protein per 3.5 oz (100 g), matching the US record almost exactly, which suggests both tables share one original analysis. — UK food composition Evidence E source
  Per 100 g: iron 37.00 mg, calcium 650 mg, protein 17.6 g, fat 15.9 g, potassium 1440 mg, zinc 5.3 mg

What a real portion looks like

• EMA describes the usual traditional dose as 1 to 3.5 g of crushed aniseed steeped in 5.1 fl oz (150 ml) of water three times a day, and advises against high-content preparations above 5 g for more than two weeks. — adults and children over 12, traditional herbal use Evidence E source
  1-3.5 g per cup, 3 times daily; > 5 g preparations not beyond 2 weeks without medical advice

What your body absorbs

• When volunteers swallowed 1, 50 or 250 mg of trans-anethole, the main flavor compound of anise, 54-69% left in urine and 13-17% as exhaled CO2, regardless of dose. — human volunteers, single doses in randomized order Evidence C source
  Urinary excretion 54-69% of dose, exhaled 14CO2 13-17%; >90% of urinary label as 4-methoxyhippuric acid

What it does to your health

• In an RCT on 107 adults with functional dyspepsia, 3 g of anise powder after each meal for 4 weeks cut the symptom score from 10.6 to 2.44, while placebo rose to 13.05. — 107 adults aged 18-65 with postprandial distress syndrome in Iran, 4 weeks of treatment, followed to week 12 (n = 107) Evidence B source
  FD severity score week 4: 2.44 vs 13.05 (P = 0.0001); week 12: 1.08 vs 13.30
• In a crossover RCT on 20 adults with chronic constipation, a tea mixing anise, fennel, elder and senna cut colonic transit time to 15.7 hours from 42.3 on placebo over 5 days. — 20 adults with chronic constipation in Brazil, 5-day periods (n = 20) Evidence B source
  Colonic transit time 15.7 h (95% CI 11.1-20.2) vs 42.3 h (95% CI 33.5-51.1), p < 0.001

Safety, limits and interactions

• The European Medicines Agency advises people allergic to celery, fennel, coriander, dill or caraway to avoid aniseed preparations, because these plants share cross-reacting allergens. — people sensitized to Apiaceae plants Evidence E source
  Contraindication for known Apiaceae or anethole sensitivity; aniseed allergenic potential described as relatively weak
• In a 2001 Dutch outbreak, 63 people fell ill and 16 had seizures after drinking a herbal tea contaminated with Japanese star anise, which contains the neurotoxin anisatin. — 63 consumers of one herbal tea, Netherlands 2001 (n = 63) Evidence D source
  63 with symptoms, 22 hospitalized, 16 with generalized tonic-clonic seizures

What people believe that the data does not support

• Star anise is a different plant from anise seed, and 7 infants given star anise tea for colic developed neurological reactions linked to contamination with toxic Japanese star anise. — 7 infants given star anise tea at home, USA (n = 7) Evidence D source
  7 cases of adverse neurologic reactions; evidence of Chinese star anise contaminated with Japanese star anise

Who this works differently for

• In an RCT on 145 mothers of preterm babies, tea with 2 g of anise three times a day for 7 days raised pumped milk volume from day 3 onward, without changing infant weight. — 145 mothers of preterm infants in Iran, 7 days (n = 145) Evidence B source
  Milk volume higher than placebo and control on days 3-7 (p < 0.05); infant weight no difference
• In an RCT on 60 menopausal women, 4 g of anise a day for 8 weeks lowered depression, anxiety and stress scores more than placebo, a single small trial still awaiting replication. — 60 menopausal women, 8 weeks (n = 60) Evidence B source
  DASS-21 lower than placebo at 8 weeks (p < 0.0001); no adverse effects reported
• In a double-blind RCT on 60 breastfeeding mothers, a herbal tea containing anise, fennel and fenugreek for 30 days caused no adverse effects in mothers or infants followed to 12 months. — 60 healthy exclusively breastfeeding mothers and their infants, 30 days, follow-up to 12 months (n = 60) Evidence B source
  No adverse effects attributable to the tea; no group differences in infant growth (all p > .05)
• The European Medicines Agency does not recommend aniseed medicines for children under 12 or in pregnancy and breastfeeding, citing missing safety data and the estragole it contains. — children under 12, pregnant and breastfeeding women Evidence E source
  Precautionary: not recommended under 12 years and in pregnancy and lactation

What is still unknown

• A Cochrane review rated the evidence that anise eases functional dyspepsia as low certainty, because it rests on a single trial of 107 people. — adults with functional dyspepsia, herbal medicine trials (n = 107) Evidence B source
  Pimpinella anisum vs placebo SMD -2.30 (95% CI -2.79 to -1.80), 1 study, low certainty

The bottom line

Food tables make anise look like an iron source, at 37 mg per 3.5 oz (100 g) in both the US and the UK records. The two numbers match almost to the decimal, which suggests one original analysis behind both, and iron in spices is often inflated by soil contamination. A teaspoon adds about 0.8 mg of iron and 7 calories, and we found no study of how much of that iron the body takes up. For trans-anethole, the main flavor compound, there is a human study, but of the pure substance. Volunteers given 1 to 250 mg passed 54 to 69 percent in urine and 13 to 17 percent as exhaled CO2, whatever the dose. The European Medicines Agency describes the usual traditional tea as 1 to 3.5 g of crushed seed in 5.1 fl oz (150 ml) of water, three times a day. The agency presents this as usual practice and cites no trial for it. It also advises against preparations with more than 5 g of seed for longer than two weeks without medical advice, as a precaution with no established harm threshold behind it. The other trials are smaller or less clean. In 145 mothers of preterm babies in Iran, tea with 2 g of anise three times a day raised the volume of pumped milk from day 3 to day 7 compared with black tea, and the babies' weight did not differ. It lasted one week, five women dropped out over the taste, and the figures we have give no absolute volumes. The European Medicines Agency does not recommend aniseed preparations while breastfeeding, as set out below. In 60 menopausal women, 4 g a day for 8 weeks lowered depression, anxiety and stress scores more than placebo. The abstract gives no effect size, and this small trial is still waiting for a second one. A tea that cut colonic transit time in 20 constipated adults from 42.3 to 15.7 hours also contained senna, and the trial did not separate any share for anise, so the result cannot be credited to anise. Who should be careful. People allergic to celery, fennel, coriander, dill or caraway share cross-reacting allergens with anise, and the European Medicines Agency advises them to avoid aniseed preparations, while calling the allergenic potential relatively weak. The same agency does not recommend aniseed for children under 12, in pregnancy or while breastfeeding, because adequate safety data are missing. That position covers medicinal preparations of the seed, and there are no clinical data on pregnancy at all. One trial of a mixed tea with fennel, anise, coriander and fenugreek in 60 breastfeeding mothers found no adverse effects in mothers or infants followed to 12 months. It tested a blend, so it says little about anise on its own. Star anise is a different plant, and the serious poisonings belong to it. Chinese star anise sold for tea has been found contaminated with Japanese star anise, which contains the nerve toxin anisatin. In the Netherlands in 2001, 63 people fell ill after drinking one contaminated herbal tea and 16 had seizures. In the US, 7 infants given star anise tea at home for colic had neurological reactions. None of these cases involved anise seed.

Sources

1. anis-daily-r7-01 · food composition dataset
   Spices, anise seed | Energy 337 KCAL per 100 g | Protein 17.6 G | Fat 15.9 G | Fiber 14.6 G | Calcium 646 MG | Iron 36.96 MG | Potassium 1441 MG | 1 tsp, whole 2.1 g
   USDA SR Legacy 2019, Spices, anise seed (FDC 171316, NDB 2002) · checked 2026-10-01
2. anis-daily-r7-02 · food composition dataset
   Anise seeds | Iron (mg) 37.00 | Calcium (mg) 650 | Protein (g) 17.6 | Fat (g) 15.9 | Potassium (mg) 1440 | Zinc (mg) 5.3
   CoFID 2021 (Public Health England, OGL v3.0), code 13-802 Anise seeds · checked 2026-10-01
3. anis-daily-r7-10 · regulatory assessment
   The following posology may be considered as usual in the practice: 1 to 3.5 g of whole or (freshly1) comminuted or crushed aniseed in 150 ml of water as a herbal tea, three times daily. ... Preparations with high aniseed content (> 5 g) should not be taken for more than two weeks without medical advice.
   European Medicines Agency, HMPC assessment report on Pimpinella anisum L., fructus and aetheroleum (EMA/HMPC/321181/2012), 2013 · checked 2026-10-01
4. anis-daily-r7-11 · pharmacokinetic trial
   The doses chosen were: 1 mg; close to the daily intake in the diet from foods, 50 mg; approximating to the amount present in a normal measure of an anise-flavoured beverage, and 250 mg. The order of administration was randomized. The major routes of elimination of 14C were in the urine (54-69% of the administered dose) and as exhaled 14CO2 (13-17%). Dose size had no systematic effect on either rate or route of excretion.
   Food Chem Toxicol, 1988 · checked 2026-10-01
5. anis-daily-r7-03 · randomized controlled trial
   Anise group included 47 patients and received anise powders, 3 g after each meal (3 times/day). ... Mean (standard deviation) total scores of FD severity scale before intervention in the anise and control groups were 10.6 (4.1) and 10.96 (4.1), respectively (P = 0.6). They were 7.04 (4.1) and 12.30 (4.3) by week 2, respectively (P = 0.0001), 2.44 (4.2) and 13.05 (5.2) by week 4, respectively (P = 0.0001), and 1.08 (3.8) and 13.30 (6.2) by week 12, respectively (P = 0.0001).
   Journal of Research in Medical Sciences, 2015 · checked 2026-10-01
6. anis-daily-r7-12 · randomized controlled trial
   This randomized, crossover, placebo-controlled, single-blinded trial included 20 patients presenting with chronic constipation according to the criteria of the American Association of Gastroenterology. ... Mean CTT assessed by X ray was 15.7 hours (95%CI 11.1-20.2) in the active treatment period and 42.3 hours (95%CI 33.5-51.1) during the placebo treatment (p < 0.001).
   BMC Complement Altern Med, 2010 · checked 2026-10-01
7. anis-daily-r7-09 · regulatory assessment
   The allergenic potential of aniseed is relatively weak and it shows up occasionally with allergic reactions at dermal, respiratory and gastro-intestinal level ... People with known sensitivity to aniseed or to Apiaceae (Umbelliferae) (caraway, celery, coriander, dill and fennel) or to anethole should avoid the use of aniseed preparations and anise oil.
   European Medicines Agency, HMPC assessment report on Pimpinella anisum L., fructus and aetheroleum (EMA/HMPC/321181/2012), 2013 · checked 2026-10-01
8. anis-daily-r7-14 · case series
   A total of 63 persons reported symptoms of general malaise, nausea and vomiting 2-4 hours following consumption of the herbal tea. Twenty-two persons required hospitalisation, of whom 16 due to generalised tonic-clonic seizures. ... NMR analysis of the herbal tea confirmed the presence of the neurotoxin anisatin, a non-competitive GABA-antagonist which can cause hyperactivity of the central nervous system and tonic-clonic seizures.
   Ned Tijdschr Geneeskd, 2002 · checked 2026-10-01
9. anis-daily-r7-13 · case series
   We report 7 cases of adverse neurologic reactions in infants seen with the home administration of star anise tea. In addition, we have found evidence that Chinese star anise has been contaminated with Japanese star anise.
   Pediatrics, 2004 · checked 2026-10-01
10. anis-daily-r7-05 · randomized controlled trial
    Overall, 145 participants with preterm infants participated in the study (50 in the intervention group, 49 in the placebo group, and 46 in the control group). ... Participants in the intervention group received Pimpinella Anisum herbal tea (2 g of dried Anise plant plus 1 g of black tea). Those in the placebo group received black tea containing 3 g of dried black tea only. In both groups, tea was ingested 3 times [ 32 – 34 ] a day for a week at breakfast, lunch, and dinnertime. ... On the third, fourth, fifth, sixth and seventh days, the mean volume of pumped milk in the intervention group was significantly higher than the placebo and control groups ( p < 0.05). There was no statistically significant difference in terms of preterm infant weight on days 0, 3 and 7 between the three groups.
    BMC Complementary Medicine and Therapies, 2023 · checked 2026-10-01
11. anis-daily-r7-06 · randomized controlled trial
    A total of 60 menopausal women received either 4 g of anise per day or a matched placebo, administered in two divided doses over an eight-week period. ... Anise significantly reduced the DASS-21 scores compared to placebo at 8 weeks (p < 0.0001).
    Current Pharmaceutical Design, 2026 · checked 2026-10-01
12. anis-daily-r7-07 · randomized controlled trial
    Healthy, exclusively/fully breastfeeding women ( N = 60) with no milk insufficiency were randomized into (1) an all-natural tea containing fruits of bitter fennel, anise, and coriander; fenugreek seed; and other herbs (Mother's Milk® herbal tea; test) group or (2) a lemon verbena leaf (placebo) group. ... RESULTS: No adverse effects attributable to the interventions were reported at any time point.
    J Hum Lact, 2019 · checked 2026-10-01
13. anis-daily-r7-08 · regulatory assessment
    As a precautionary measure, the use of aniseed is not recommended in children under 12 years of age due to the lack of adequate data for safety assessment. ... In the absence of sufficient data, the use of aniseed and aniseed preparations during pregnancy and lactation is not recommended.
    European Medicines Agency, HMPC assessment report on Pimpinella anisum L., fructus and aetheroleum (EMA/HMPC/321181/2012), 2013 · checked 2026-10-01
14. anis-daily-r7-04 · systematic review
    Pimpinella anisum (SMD -2.30, 95% CI -2.79 to -1.80; 1 study, 107 participants; low CoE).
    Cochrane Database of Systematic Reviews, 2023 · checked 2026-10-01