What Is It?
Health Benefits

Dosage Information

Guidelines for Use

General Interaction

Possible Side Effects



Evidence Based Rating Scale

What Is It?

Most cooks--even unadventurous ones--can easily identify the yellowish-brown crescents known as fennel seeds. That is because these tiny seeds, which actually represent the dried ripe fruits of the aromatic fennel plant (Foeniculum vulgare), have been handed down through the ages as a spice and food preservative. Their heady and memorable flavor, reminiscent of licorice and anise, is familiar to most people because fennel seeds are used in various foods including breads, Italian sausages, and sauerkraut. The stems and leaves of the fennel plant are edible and are added to various foods such as fish, meats, vegetables and salads. The large leafstalk base of one variety is eaten as a vegetable, both raw and cooked. Seeds and leaves can be used to make a tea. Fennel is a member of the Apiaceae family, which also includes carrots and parsley. (1)

There are many varieties of fennel but the two main varieties are sweet fennel and bitter fennel. Sweet fennel (Foeniculum vulgare var. dulce) is native to the Mediterranean and is cultivated in France, India, Iran, Italy, Morocco, and the United States. Bitter fennel (Foeniculum vulgare var. Mill) is grown in Argentina, central Europe, Germany, Hungary, Russia, and the United States. Bitter fennel is the most common variety in the United States. (2) The official fennel oil of the European Pharmacopeia is derived from the seed of the bitter fennel variety. It has a higher concentration of the main therapeutic constituents of fennel. (3)

In addition to keeping fennel as a kitchen staple, people in China, Europe, and other parts of the world continue to use fennel seeds in teas, tinctures, and compresses to relieve myriad ailments, including stomach upset, gas, and coughs. Scientists have even looked into fennel's value as a source for synthetic estrogen. Although evidence to support these and other uses is spotty, fennel seeds appear to help certain conditions.

Chewing on fennel seeds has traditionally been used to vanquish bad breath. You may have noticed them (sometimes candy coated) in a small bowl near the exit of Indian restaurants. Specially made fennel-flavored syrups appear to help ease coughs, and are widely used for this purpose in Europe. One source indicates a tea containing fennel and seven other herbs improved sleep discomfort, cough frequency, and cough intensity in patients with allergic asthma. (4) And relief from stomach upset may be found with a gentle fennel tea made by simmering 1 to 2 teaspoons of bruised seeds in 8 ounces of water.

Health Benefits

Fennel has been shown to have antioxidant and preservative properties. In large animal breeding, semen is often preserved by cryopreservation (freezing) for later use. Freezing “extenders” may be added in order to increase the time that specimens can be kept alive. A 2011 animal study evaluated the effect of various concentrations of fennel added to the freezing extender of boar semen for cryopreservation. Higher concentrations of fennel improved sperm viability and motility upon thawing when compared to samples without fennel. Studies are needed to determine benefit for men who wish to preserve semen, e.g., when undergoing cancer treatment. (5)

Fennel has been used to treat colic in breast-fed infants. When a healthy baby has sustained bouts of crying (more than three hours a day) over several weeks, it may be from “colic”. A small study was done to evaluate the safety and efficacy of ColiMil®, a compound containing 164 milligrams of fennel, 97 milligrams of lemon balm, and 178 milligrams of German chamomile. Ninety-three colicky breast-fed infants were observed for three days then given either ColiMil or placebo twice a day for one week. Results showed crying time was reduced by 85% in the ColiMil® group compared to 48% in the placebo group. ColiMil was found to be safe in breast-fed infants when used for one week. (6)

Traditionally, fennel has been used to treat dyspepsia, or upset stomach, and upper respiratory inflammation. The seeds and oil are approved by the German Commission E for the short-term treatment of these conditions. (1)

Specifically, fennel may help to:

Relieve constipation. An herbal compound containing anise, elderberry, bitter fennel, and senna that is used in Brazil for the treatment of constipation was evaluated for its safety and efficacy in a 2010 study. Twenty patients with chronic constipation received either the compound or placebo for a five-day period. After five days, there was a nine-day period of no treatment followed by another five-day period when patients received the opposite treatment. The study results indicate the compound is a safe and effective laxative for the treatment of constipation. (7)

Treat flatulence. Fennel is traditionally used to eliminate flatulence and regulate intestinal function. It is approved by the German Commission E for the treatment of flatulence. (1) However, one source described premature thelarche, a disorder characterized by breast development in children younger than six years of age, in four children with long-term use of fennel preparations. Their estrogen levels were found to be elevated, and the premature breast development receded with discontinuation of the herb. Long-term use of fennel and other herbal preparations should be avoided in children. (8)


  • oil
  • powder (capsules)
  • seed
  • syrup
  • tablet
  • tea
  • tincture

Dosage Information

There are no typical dosages of fennel. Traditionally, a tea is prepared from 1-2 grams of crushed dried seeds in 150 milliliters of boiling water (about 2/3 cup) that may be taken 2-3 times daily between meals. Use should be limited to 5-7 total grams per day of crushed or ground seeds.

The common dose of the tincture (1:5 grams/milliliter) is 5-15 milliliters (1-3 teaspoons) 2-3 times daily between meals

Fennel oil in the amount of 0.1-0.6 milliliters should only be used for up to two weeks without evaluation by a physician and should be avoided during pregnancy due to risk of miscarriage.

Fennel honey syrup containing 500 milligrams of fennel oil per kilogram is usually dosed at 10-20 grams per day.

The common dose of the fluid extract 1:1 (grams/milliliter): 1-3 milliliters 2-3 times daily between meals

Guidelines for Use

Fennel oil can cause nausea, vomiting, and seizures in amounts as small as one milliliter and should not be used by home cooks. (1) Fennel oil in the amount of 0.1-0.6 milliliters should only be used up to two weeks without professional evaluation.

General Interaction

  • Consuming fennel while taking ciprofloxacin may reduce the effectiveness of the drug and slow its elimination.

  • Fennel may interfere with hormonal therapy including birth control medications by competing for estrogen sites.

  • Consuming large doses of fennel may reduce the anti-estrogenic effect of tamoxifen and other estrogen receptor modulators.

Possible Side Effects  

Fennel can cause allergic reactions in the skin and respiratory system. Photodermatitis, a rash that occurs after exposure to sunlight also known as sun poisoning, may also occur. Fennel may cause allergic reactions in people who are sensitive to carrot, celery, or mugwort.  


Fennel seeds pose no risk when used as a culinary spice or fragrance. And centuries of use suggest that taking recommended amounts of fennel seeds for healing is safe as well.  

While most fennel preparations made from the seeds (teas, syrups, tinctures) pose no apparent health risks, avoid ingesting pure fennel oil because it can cause nausea, breathing problems, and other complications.  

Because pure fennel oil contains concentrated levels of a substance with estrogen-like action, women who have a hormone-sensitive condition such as uterine fibroids or endometriosis; who have an estrogen sensitive cancer; or who are pregnant or breast-feeding should avoid medicinal quantities. (9) One case report from the 1990s indicates that the consumption of herbal teas containing fennel may poison the nervous system of breast-feeding infants. This condition is known as neurotoxicity. However, the full report is not readily available, and it is unknown what quantities were consumed and how the association was confirmed. (10) 


1. The Herb Society of America—Fennel. Available at Accessed March 11, 2012.
2. Raghavan S. Handbook of spices, seasonings, and flavorings. 2nd ed. Boca Raton, FL:CRC Press Taylor and Francis Group, LLC;2007:107-108.
3. American Botanical Council Herbalgram—Fennel Oil. Available at Accessed March 20, 2012.
4. Haggag EG, Abou-Moustafa MA, Boucher W, Theoharides TC. The effect of a herbal water-extract on histamine release from mast cells and on allergic asthma. J Herb Pharmacother. 2003;3(4):41-54.
5. Malo C, Gil L, Cano R, González N, Luño V. Fennel (Foeniculum vulgare) provides antioxidant protection for boar semen cryopreservation. Andrologia. 2011 Nov 23. doi: 10.1111/j.1439-0272.2011.01254.x.
6. Savino F, Cresi F, Castagno E, et al. A randomized double-blind placebo-controlled trial of a standardized extract of Matricariae recutita, Foeniculum vulgare and Melissa officinalis (ColiMil) in the treatment of breastfed colicky infants. Phytother Res 2005;19:335-40.
7. Picon PD, Picon RV, Costa AF, Sander GB, Amaral KM, Aboy AL, Henriques AT. Randomized clinical trial of a phytotherapic compound containing Pimpinella anisum, Foeniculum vulgare, Sambucus nigra, and Cassia augustifolia for chronic constipation. BMC Complement Altern Med. 2010 Apr 30;10:17.
8. Türkyilmaz Z, Karabulut R, Sönmez K, Can Başaklar A. A striking and frequent cause of premature thelarche in children: Foeniculum vulgare. J Pediatr Surg. 2008 Nov;43(11):2109-11.
9. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.
10. Rosti L, Nardini A, Bettinelli ME, Rosti D. Toxic effects of a herbal tea mixture in two newborns. Acta Paediatrica 1994;83:683.

Evidence Based Rating Scale

The Evidence Based Rating Scale is a tool that helps consumers translate the findings of medical research studies and what our clinical advisors have found to be efficacious in their personal practice into a visual and easy to interpret format. This tool is meant to simplify the information on supplements and therapies that demonstrate promise in the treatment of certain conditions.








Traditional use and a tea containing fennel and seven other herbs improved sleep discomfort, cough frequency, and cough intensity in patients with allergic asthma. (4)

Bad Breath  

Traditional use but no studies supporting its efficacy.


Traditional use and approved by German Commission e for respiratory inflammation. No studies specifically for cough using it as a single herb. (1, 4) 

One small study indicates it is a safe and effective laxative in combination with other herbs. (7)
Approved by German Commission E; however, long-term use in children should be avoided. (1, 8)
Infertility, Male  
Extends the life of frozen semen in animals. Human studies are needed. (5)

Date Published: 04/18/2005
Previous  |  Next
> Printer-friendly Version Return to Top