Fennel is used as both a cooking ingredient and a traditional remedy, with its bulb, seeds, and fronds each serving different purposes in the kitchen and in herbal medicine. Its most well-supported health uses center on digestive relief, menstrual pain, and infant colic, though it also appears in traditional treatments for respiratory complaints and low breast milk supply. The plant contains 4 to 6% volatile oil, with the compound anethole making up 50 to 60% of that oil and driving most of its medicinal and flavor properties.
Digestive Relief: Bloating, Gas, and IBS
Fennel’s oldest and best-known use is settling the stomach. Crushed fennel seeds steeped in boiling water produce fennel water, a classic remedy for flatulence that works through the oil’s carminative properties, meaning it helps the body expel trapped gas. The mechanism is more nuanced than simple gas relief, though. Lab research published in Neurogastroenterology & Motility found that fennel tea has region-specific effects on stomach muscle: it relaxes the upper portions of the stomach (reducing cramping and spasm) while simultaneously increasing contractions in the lower stomach, which helps push food along. That combination explains why fennel can ease both the bloating feeling and the sluggish digestion that often accompanies it.
For people with irritable bowel syndrome, one clinical trial found that 30 days of treatment with fennel oil combined with curcumin extract significantly decreased abdominal pain and distension while improving quality of life, with no notable side effects. Fennel tea on its own is commonly used for milder everyday complaints like post-meal bloating or nausea.
Infant Colic
One of fennel’s most studied pediatric applications is for colic in newborns. A randomized, placebo-controlled trial found that a fennel seed oil emulsion eliminated colic (defined by the standard Wessel criteria of crying more than three hours a day) in 65% of treated infants, compared to just 24% in the placebo group. No side effects were reported during the trial. Separately, fennel tea given three times daily at 35 mL significantly reduced crying hours within one week. These are small studies, but the consistency of results across them is notable, and fennel-based “gripe water” products remain widely available for this reason.
Menstrual Pain
Fennel extract performs surprisingly well against conventional painkillers for period cramps. A clinical trial published through the WHO’s Eastern Mediterranean Health Journal compared fennel extract to mefenamic acid (a prescription-strength anti-inflammatory commonly used for menstrual pain) in adolescent girls with primary dysmenorrhea. After treatment, 80% of the fennel group reported complete pain relief or significant pain reduction, compared to 73% in the mefenamic acid group. The difference between the two treatments was not statistically significant, meaning fennel worked about as well as the pharmaceutical. Girls in the fennel group were also more likely to resume normal activity without needing rest.
Breast Milk Production
Fennel has a long history as a galactagogue, a substance believed to increase breast milk supply. The clinical evidence here is weaker than for digestive or menstrual uses. Two small studies found increases in milk volume, fat content, and infant weight gain with fennel, but both had significant design limitations: small sample sizes, unclear blinding, and in one case, no randomization at all. A larger study of 158 breastfeeding mothers in Iran using an herbal mixture containing fennel, anise, cumin, and other herbs found no difference in infant weight gain compared to placebo. Another trial using a commercial lactation tea containing fennel alongside fenugreek, goat’s rue, and other herbs did show increased milk production on the third day postpartum, but since the tea contained multiple ingredients, fennel’s individual contribution is impossible to isolate. The tradition persists, and fennel tea is unlikely to cause harm in moderate amounts, but the evidence doesn’t strongly support it as a standalone solution for low milk supply.
Estrogenic Effects and Safety Concerns
Fennel contains compounds that can mimic estrogen in the body, which is relevant both to its benefits (likely explaining its effects on menstrual symptoms) and its risks. If you have a hormone-sensitive condition like breast cancer, ovarian cancer, endometriosis, or uterine fibroids, fennel in medicinal amounts could potentially worsen those conditions. Large amounts of fennel may also interfere with medications that interact with estrogen, including tamoxifen and hormonal birth control pills. If you take birth control pills and consume fennel in supplement-level quantities, using a backup contraceptive method is a reasonable precaution. Culinary amounts, like fennel bulb in a salad or a pinch of seeds in cooking, are generally not a concern.
Typical Doses
For digestive purposes, fennel seeds are traditionally used in doses of 5 to 7 grams, either chewed directly or steeped as tea. Fennel seed oil is used at much smaller amounts, typically 0.1 to 0.6 mL. For postmenopausal symptoms, clinical studies have used essential fennel oil capsules at 200 mg per day. These are the ranges found in the existing clinical literature, not standardized prescriptions, so individual responses will vary.
Cooking With Fennel
Unlike most herbs, fennel offers three distinct edible parts. The bulb has a crisp, celery-like texture and a mild licorice flavor that mellows when roasted or sautéed. Raw, it works well shaved thin in salads. The seeds are more intensely flavored and are used to season sausage (particularly Italian varieties), form crusts for fish or beef, and pickle vegetables. The feathery fronds make a delicate garnish with a light anise taste, suitable for finishing soups or topping fish dishes.
Fennel seeds pair especially well with seafood and pork. The bulb is a good source of fiber, with one raw bulb providing over 7 grams, along with meaningful amounts of potassium, calcium, and phosphorus. Roasting the bulb caramelizes its natural sugars and significantly softens the licorice notes, making it a good entry point for people who find raw fennel’s flavor too assertive.
Blood Sugar Research
Early animal research suggests fennel leaf extract may help lower blood sugar levels. In one study, diabetic rats given fennel leaf extract at various doses showed significant reductions in blood glucose over 30 days, along with increased insulin levels and physical improvement in the insulin-producing cells of the pancreas. Researchers attribute this to phenolic acids in the leaves, including caffeic acid and chlorogenic acid, both of which have shown blood-sugar-lowering properties in other research. This is strictly animal data at this point, with no human clinical trials to confirm the effect or establish a useful dose.