Fennel has been used for centuries as a traditional remedy to boost breast milk, but there is no reliable scientific evidence that it works. The Academy of Breastfeeding Medicine reviewed the available research and concluded it cannot recommend fennel or any other herbal galactagogue (a substance believed to increase milk production) due to insufficient evidence of effectiveness and potential safety concerns.
Why Fennel Is Believed to Help
The idea behind fennel as a milk booster centers on a compound called anethole, which gives fennel its licorice-like flavor. Anethole has a chemical structure that loosely resembles estrogen, and some traditional practitioners have theorized it could stimulate hormones involved in milk production. This theory has never been confirmed in well-designed human studies. The Academy of Breastfeeding Medicine notes that the mechanisms of action for most herbal galactagogues are simply unknown.
What the Research Actually Shows
Despite fennel’s long history of traditional use, clinical studies testing whether it increases milk volume are scarce, small, and poorly designed. The available research on herbal galactagogues in general suffers from small numbers of participants, lack of randomization, and missing controls. None of the stronger studies on milk volume in mothers of preterm infants found fennel specifically among the herbs with even low-certainty evidence of benefit. Other herbs like anise seed tea and barley malt showed modest increases in milk volume by day 7, on the order of 80 to 150 ml per day, but fennel was not among them.
The fact that fennel has been used for centuries without widespread reports of harm is somewhat reassuring, but “long history of use” is not the same as evidence that something works. Many traditional remedies persist through cultural momentum and the placebo effect rather than proven results.
Safety Risks Worth Knowing About
The bigger concern with fennel during breastfeeding is not whether it works but whether it’s safe in large amounts. In one documented case, two newborns (15 and 20 days old) were hospitalized after their mothers drank excessive amounts of an herbal tea containing fennel and anise. Both infants showed concerning symptoms: lethargy, weak muscle tone, vomiting, a weak cry, poor sucking, and reduced responses to pain. One of the mothers also reported feeling drowsy and weak herself. Both infants improved within 24 to 36 hours after their mothers stopped the tea and breastfeeding. The suspected cause was anethole passing through breast milk, though levels were never directly measured.
This case involved heavy consumption of a blended herbal tea, not a single cup of fennel tea. Still, it illustrates that anethole can reach the infant through breast milk in quantities large enough to cause real harm. Fennel is not regulated as a medication, so the concentration of active compounds varies widely between products.
Allergic Reactions
Fennel belongs to the same plant family as carrots, celery, and parsley. If you or your baby has a known allergy to any of these foods, fennel may trigger a cross-reaction. Allergic responses can affect the skin or respiratory system, and fennel has also been associated with increased sun sensitivity.
Fennel Tea vs. Fennel Essential Oil
There is an important distinction between sipping fennel seed tea and using concentrated fennel essential oil. Essential oils contain far higher concentrations of anethole than a cup of tea made from whole seeds. The toxicity case described above involved herbal tea, not essential oil, which means even tea-strength preparations can pose risks in large quantities. Concentrated fennel oil taken orally during breastfeeding carries a much higher risk of exposing your baby to problematic levels of anethole.
What Works Better for Low Milk Supply
If you’re worried about your milk supply, the most effective interventions are not herbal. Frequent, effective breast emptying is the primary driver of milk production. That means nursing or pumping at least 8 to 12 times per day in the early weeks, ensuring your baby has a good latch, and avoiding long stretches without emptying the breast. Skin-to-skin contact also supports the hormonal signals that drive milk production.
For mothers who have tried optimizing breastfeeding technique and still have genuinely low supply, prescription medications exist that have somewhat more evidence behind them, though even those come with caveats. The Academy of Breastfeeding Medicine emphasizes that no galactagogue, pharmaceutical or herbal, should replace proper breastfeeding evaluation and support. A lactation consultant can help identify whether you truly have a supply issue or whether something else, like latch problems or feeding frequency, is the root cause.
Many mothers who feel their supply is low are actually producing enough milk. Perceived low supply is more common than actual low supply, and the anxiety itself can become a barrier to comfortable breastfeeding. Before reaching for fennel tea or any supplement, getting a professional assessment of how feeding is going can save time, money, and worry.