Herbs & Botanicals
Fennel (xiao hui xiang)
What is fennel?
Fennel is a bulbous plant native to southern Europe and western Asia.
It is a member of the celery family and is well-known for its distinctive
flavor. Although the entire plant is edible, only fennel seeds and essential
oils are used for their medicinal properties.
Why do we need fennel? What is it used for?
Fennel seeds contain an essential oil, which is composed of anethole,
fenchone, estragole, and other vital enzymes and compounds. Anethole may
have estrogen-like qualities and can reduce spasms in smooth muscles,
such as those in the intestinal tract.
Recent studies have found that fennel seeds contain diuretic, pain-reducing,
fever-reducing and antimicrobial properties. Some practitioners believe
it can be used to aid indigestion and increase the production of milk
in nursing women.
Studies on fennel's essential oil are less clear. Some studies have linked
the oil to possible liver damage, while other studies have found that
a compound made from anethole protects against liver toxicity.
How much fennel should I take?
The German Commission E Monographs recommend between 5-7 grams of fennel
seeds daily. The plant can also be ingested as a tincture (2-4 milliliters,
three times daily).
What forms of fennel are available?
Whole fennel seeds are available at health food stores and many supermarkets.
Patients can also purchase fennel tinctures, which contain a percentage
of the oil in an alcohol base.
What can happen if I take too much fennel? Are
there any interactions I should be aware of? What precautions should I
While no significant adverse reactions have been reported, in rare cases,
fennel seeds can cause allergic reactions on the skin and respiratory
problems. Excess amounts of fennel oil may cause nausea, vomiting and
seizures. In addition, anyone suffering from an estrogen-dependent form
of cancer should avoid any large quantities of fennel and consult their
At present, there are no well-known drug interactions associated with
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- Mills SY. Out of the Earth: The Essential Book
of Herbal Medicine. Middlesex, UK: Viking Arkana, 1991, pp. 4246.
- Albert-Puleo M. Fennel and anise as estrogenic agents.
J Ethnopharm 1980;2(4):33744.
- Tanira MOM, Shah AH, Mohsin A, et al. Pharmacological
and toxicological investigations on foeniculum vulgare dried
fruit extract in experimental animals. Phytother Res 1996;10:336.
- Blumenthal M, Busse WR, Goldberg A, et al. (eds).
The Complete Commission E Monographs: Therapeutic Guide to Herbal
Medicines. Boston, MA: Integrative Medicine Communications, 1998,