From Westfall RE. Galactagogue herbs: a qualitative study and review. Canadian Journal of Midwifery Research and Practice. 2003, 2(2):22-27.
Medicinally, fennel is widely used as a digestive aid and as a treatment for dyspepsia (Blumenthal et al., 2000). It has mild estrogenic properties (Bingel and Farnsworth, 1991). Fennel is also used to counteract infant colic, whether consumed by the mother or given directly to the infant (Weed, 1986; Weizman et al., 1993). The effectiveness of an herbal colic remedy containing fennel, chamomile, vervain, licorice, and lemon balm has been demonstrated in a clinical trial (Weizman et al., 1993). However, this formula was given directly to the babies, so it remains clinically unproven that the beneficial effects of the herbs would reach the infant through the mother’s milk.
The Wise Woman Herbal (Weed, 1986) suggests that breastfeeding women use the seeds of fennel (Foeniculum vulgare Miller [Apiaceae]) or any of its close relatives (anise, cumin, caraway, coriander and dill) to improve their milk supply. Although clinical evidence for its efficacy is lacking, fennel seed has enjoyed centuries of use as a galactagogue. Its mechanism of action is unknown.
In Italy, a galactagogue tea is made from the seeds of fennel and anise (Pimpinella anisum L. [Apiaceae]) (Rosti et al., 1994). Two case reports from that country (Rosti et al., 1994) describe temporary central nervous system depression in infants, 15 and 20 days old, whose mothers were consuming large quantities of fennel and anise tea. All symptoms disappeared once the women stopped drinking the tea. However, these appear to have been isolated cases, so it is possible that a particular batch of the tea was adulterated with another, more toxic herb. In the absence of further evidence, one can assume that this age-old remedy is safe.
There are no known contraindications for use of fennel seed or fennel oil during lactation, but it is not recommended for use for more than a few weeks at a time (Blumenthal, 2000).