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Botanical Description & Habitat

Foeniculum officinale


Common names

Bitter fennel
Common fennel
Florence fennel
Garden fennel
Large fennel
Sweet fennel
Wild fennel

Found in southern Europe, India, and the United States, although it is purported to have originated in the Mediterranean area.

It has a perennial root producing a bright green annual stem. The stem grows three to four feet in height, and is smooth, erect, and glaucous.

The leaves are pinnate, grow alternately along the stem, and possess long, pointed, smooth, deep green leaflets. Yellow flowers grow in large compound umbels from July to October. The seeds are grayish-green in color and are oblong oval.

It resembles poison hemlock in appearance.

Medicinal parts
fruits - dried, from cultivated plant.

Historical Properties & Uses

Fennel is one of the most popular aromatic herbs. Its seeds contain essential oils very similar in structure and activity to those of catnip and peppermint. Whereas catnip oils are considered better suited for infant colic, fennel is the best adult choice for indigestion and flatulence.

Fennel is a popular carminative wherever it grows, including North America, Europe, Asia, and Australia. Its essential oil imparts characteristic aromatic actions, including carminative, stomachic, cholagogue, expectorant, and antispasmodic effects. The herb's galactagogue and emmenagogue properties have not been experimentally investigated. However, much excellent research demonstrates its estrogenic activity.

Fennel seed was used as a dietary aid as long ago as the first century. It probably does not directly affect weight, but rather has a healthful tonic effect on the gastrointestinal tract during dieting.It is reputed to suppress appetite.

Fennel seed and oil have approval status by the German Commission E for peptic discomforts, flatulence and catarrh.


Blumenthal, M (Ed.): The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. American Botanical Council. Austin, TX. 1998.

Method of Action

Fennel Seed has a variety of effects dependent on its oil
The carminative, stomachic, cholagogue, gastric stimulant and antispasmodic properties of this herb are probably due to the ability of its essential oil to stimulate bile secretion through an action on the vagus nerve.

The spasmolytic property the essential oil of fennel has been observed in mice. The essential oil also has a general depressive effect on motor activity in mice.

Fennel has good antibacterial properties
Antibacterial properties have been discovered in fennel oil. It is active against both gram negative and gram positive bacteria, including Streptococcus faecalis, Bacillus cereus, Salmonella enteritidis and Staphylococcus aureus.

Fennel has estrogenic effects
The galactagoggue and emmenagogue properties, known and taken advantage of during the past several centuries, have not been directly investigated. However, it is interesting to note that as late as 1916, the National Standard Dispensatory described how an infusion of fennel could be used "to increase the lacteal secretion, and to establish menstrual flow."

The galactagogue and emmenagogue properties may rely on estrogenic substances present in fennel. Estrogenic activity was first demonstrated in 1938, at which time fennel was selected for study by Sir Charles Dodds, who developed the first humanly synthesized, orally effective estrogen.

The estrogenic activity of fennel constituent anethole was repeatedly demonstrated in subsequent years. Anethole causes the growth of the lobule-alveolar system in the mammary glands of immature female rabbits, and induces estrus in mice and other experimental animals, among other estrogenic effects. Fennel oil has been shown to be five times more active than synthesized, or pure, anethole. This may be related to the degree of polymerization in the natural oil.

Drug Interactions & Precautions

Possible Interactions
The adrenocortical or corticosteroidal action of fennel may be antagonized by the use of heparin. However, the presence of estrogen like substances in this herb may increase the production of procoagulant factors which, in turn, may inhibit the anticoagulant action of heparin or coumarin.

Conversely, the estrogenic constituents of this plant may also potentiate oral antidiabetics, folic acid agonists, and some corticosteroids.

The presence of estrogen in fennel can inhibit antihypercholesterolemics by inducing hyperlipemia, and can also inhibit the activity of most parenteral medications by reducing the rate of spreading.

The estrogenic activity of fennel may be inhibited by meprobamate and phenobarbital. Due to the presence of estrogenic substance, oxytocin may augment the neural conductivity and conductivity activity of uterine smooth muscle, while the estrogen in fennel may raise blood glucose levels enough to alter insulin requirements in diabetics.

Since fennel is high in iron, it may interfere with the absorption of tetracyclines if large quantities are ingested within two hours of taking the drug. Furthermore, animal studies indicate iron plus allopurinol may lead to increased hepatic iron concentration.

The use of large amounts of fennel on a continuous basis may partially block the digestion, absorption or resorption of a wide variety of drugs and fat-soluble vitamins.

Fennel may potentiate the effects of oral anticoagulants, to the extent it stimulates the liver to catabolize and excrete cholesterol and its by-products via the biliary route.

Conversely, due to the presence of apiole fennel may inhibit certain liver microsomal hydroxylating systems, and may thereby produce toxicity from drugs normally metabolized by those systems.

There is evidence to show combining bactericidal and bacteriostatic agents will lower the effectiveness of the bacteriostatic agent. However, how this finding applies to herbal anti-infectives is still unknown.

Safety Factors & Toxicity

Oral administration of 50 grams of the fresh plant to a rabbit produced no toxic symptoms.

Fennel is generally regarded as safe by the FDA.

Occasional allergic reactions have been reported, ingestion of the volatile oil directly can produce toxicity.

Fennel seed and oil have approval status by the German Commission E.

The German Commission E recommends a limited duration for the use of fennel oil of several weeks, only.

Similarly, the seed should be used for a similar period, unless authorized by a physician or pharmacist.


Blumenthal, M (Ed.): The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. American Botanical Council. Austin, TX. 1998.

Preparation & Administration

Recommended daily dosages in Germany are as follows:

Fennel oil: 0.1 - 0.6 ml or 0.1 - 0.6 g of herb.

Fennel honey syrup (for children) contains 0.5 g fennel oil/kg.

Fennel seed preparations contain:

5 - 7 g herb.
10 - 20 g fennel syrup or honey.
5 - 7.5 g fennel tincture.

The German Commission E recommends a limited duration for the use of fennel oil of several weeks, only.

Similarly, the seed should be used for a similar period, unless authorized by a physician or pharmacist.


Blumenthal, M (Ed.): The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. American Botanical Council. Austin, TX. 1998.


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Essential Oil

See Fennel Essence under Aromatherapy


Foeniculum officinale

? Southwest School of Botanical Medicine