Side Effects of Fennel

Fennel is an herb belonging to the carrot family used to treat respiratory congestion, flatulence, constipation and bad breath, according to Health-care-tips.org. It is sometimes found in cold remedies as it is shown to have a soothing effect on sore throat and relieve cough, according to the website.

Nervous System Disruption

• Fennel, when taken in excess, may have an adverse effect on the nervous system, triggering seizures or hallucinations according to Heath-care-tips.org. People who suffer from epilepsy and other seizure disorders should not take fennel without consulting a doctor, according to Drugs.com.

Bleeding

• Fennel may interact with blood-thinning drugs to further increase the risk of bleeding, according to Healthline.com. Fennel should not be taken with aspirin, anticoagulants, blood-thinners or anti-inflammatory drugs such as ibuprofen or naproxen. Fennel may also interact with other herbs and supplements, such as ginkgo biloba, garlic and saw palmetto increasing the risk of bleeding, according to the website.

Dermatitis

• Atopic dermatitis (including itchy skin, redness and rash) and photosensitivity (increased skin sensitivity to the sun) are the most common reactions to fennel, according to Healthline.com.

Respiratory Reaction

• Bronchial asthma, hay fever and inflammation of the nasal membranes and lining of the eyes and eyelids have been reported in some fennel users, according to Healthline.com. Consult a doctor before taking fennel if you suffer from asthma or respiratory allergy symptoms.

Allergic Reaction

• Allergic reactions to fennel are rare, according to Drugs.com, but can occur and may include severe symptoms such as breathing difficulty, swelling of tongue, lips or face, and closing of throat. This type of allergic response, known as anaphylaxis, can be life-threatening and requires emergency medical attention. Other allergy symptoms include vomiting, upset stomach, convulsions and severe skin reactions such as extreme itching or hives. People with known allergies to celery or carrots should not take fennel, according to Healthline.com.