Overview

Fennel (Foeniculum vulgare) is an herb with yellow flowers. The dried seeds are used in food. The dried seeds and oil are also used as medicine.

Fennel is native to the Mediterranean, but is now found throughout the world. As medicine, it might relax the colon, and also appears to contain an ingredient that may act like estrogen in the body. As a spice, fennel has an anise-like taste.

People use fennel for menstrual cramps. It is also used for excessive crying in infants (colic), indigestion, and symptoms of menopause, but there is no good scientific evidence to support most of these uses.

Uses & Effectiveness

Possibly Effective for

There is interest in using fennel for a number of other purposes, but there isn't enough reliable information to say whether it might be helpful.

Side Effects

When taken by mouth: Fennel is commonly consumed in foods. It is possibly safe when used as medicine at appropriate doses for a short period of time. There isn't enough reliable information to know whether fennel is safe when used long-term. Although rare, side effects might include stomach upset and seizures.

When applied to the skin: Fennel is possibly safe. Fennel can make skin extra sensitive to the sun and make it easier to get a sunburn. Wear sunblock if you are light-skinned.

Special Precautions and Warnings

When taken by mouth: Fennel is commonly consumed in foods. It is possibly safe when used as medicine at appropriate doses for a short period of time. There isn't enough reliable information to know whether fennel is safe when used long-term. Although rare, side effects might include stomach upset and seizures.

When applied to the skin: Fennel is possibly safe. Fennel can make skin extra sensitive to the sun and make it easier to get a sunburn. Wear sunblock if you are light-skinned.

Pregnancy: Fennel is possibly unsafe to use when pregnant. Regularly using fennel has been linked to preterm birth.

Breast-feeding: Fennel is possibly unsafe. There are some reports of breast-feeding infants with damage to their nervous systems after they were exposed to herbal tea containing fennel through breastmilk.

Children: Fennel is possibly safe when used at appropriate doses for up to one week in young infants with colic.

Allergy to celery, carrot or mugwort: Fennel might cause an allergic reaction in people who are sensitive to these plants.

Bleeding disorders: Fennel might slow blood clotting. Taking fennel might increase the risk of bleeding or bruising in people with bleeding disorders.

Hormone-sensitive condition such as breast cancer, uterine cancer, ovarian cancer, endometriosis, or uterine fibroids: Fennel might act like estrogen. If you have any condition that might be made worse by estrogen, do not use fennel.

Interactions

    Moderate Interaction

    Be cautious with this combination

  • Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs) interacts with Fennel

    Fennel might slow blood clotting. Taking fennel along with medications that also slow blood clotting might increase the risk of bruising and bleeding.

  • Medications changed by the liver (Cytochrome P450 3A4 (CYP3A4) substrates) interacts with Fennel

    Some medications are changed and broken down by the liver. Fennel might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.

  • Birth control pills (Contraceptive drugs) interacts with Fennel

    Some birth control pills contain estrogen. Large amounts of fennel might affect estrogen levels in the body. Taking fennel along with birth control pills might decrease the effects of birth control pills. If you take birth control pills along with fennel, use an additional form of birth control such as a condom.

  • Ciprofloxacin (Cipro) interacts with Fennel

    Ciprofloxacin is an antibiotic. Fennel might decrease how much ciprofloxacin the body absorbs. Taking fennel along with ciprofloxacin might decrease the effects of ciprofloxacin. To avoid this interaction, take fennel at least one hour after ciprofloxacin.

  • Estrogens interacts with Fennel

    Large amounts of fennel might have some of the same effects as estrogen. Taking fennel along with estrogen might decrease the effects of estrogen.

  • Tamoxifen (Nolvadex) interacts with Fennel

    Large amounts of fennel seem to affect estrogen levels in the body. Taking fennel along with tamoxifen might decrease the effects of tamoxifen.

Dosing

Fennel is available in many different types of products, including essential oils, seed extracts, seed powders, teas, and creams. There isn't enough reliable information to know what an appropriate dose of fennel might be. Keep in mind that natural products are not always necessarily safe and dosages can be important. Be sure to follow relevant directions on product labels and consult a healthcare professional before using.
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CONDITIONS OF USE AND IMPORTANT INFORMATION: This information is meant to supplement, not replace advice from your doctor or healthcare provider and is not meant to cover all possible uses, precautions, interactions or adverse effects. This information may not fit your specific health circumstances. Never delay or disregard seeking professional medical advice from your doctor or other qualified health care provider because of something you have read on WebMD. You should always speak with your doctor or health care professional before you start, stop, or change any prescribed part of your health care plan or treatment and to determine what course of therapy is right for you.

This copyrighted material is licensed from Therapeutic Research Center, LLC. Information from this source is evidence-based and objective, and without commercial influence. For professional medical information on natural medicines, see Natural Medicines Comprehensive Database Professional Version.
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