Fennel, one of the oldest plants used in herbal medicine, is a native herb of the Mediterranean region. Cultivated since the Middle Ages, fennel has been used medicinally and in cooking across the USA, Europe, Asia and Africa. The fennel plant grows flower clusters, which contain new seeds. Mature flowers provide the seeds that are harvested, dried, crushed and brewed to produce a medicinal tea. Before you begin using fennel tea, consult with your health care provider to determine if and how much fennel tea is safe for you to drink.
Fennel tea has been used medicinally to treat or prevent many conditions, including coughs, bronchitis, sinus congestion, gastrointestinal discomfort and other ailments. However, in some cases, drinking fennel tea, especially in excess, can be harmful. Drinking large amounts of fennel tea can trigger muscle spasms and, in rare cases, hallucinations, according to Bitterroot Restoration.
Fennel may decrease your body's ability to absorb the antibiotic Ciprofloxacin. It might also interfere with benefits of anti-seizure medications, according to Drugs.com. Fennel may increase the risk of seizures, so if you have a seizure disorder, such as epilepsy, do not take fennel without first discussing it with your health practitioner. While there is no recommended limit on fennel tea, try to drink one cup at a time until you know how you react to fennel. If you begin to experience muscle spasms or weakness, discontinue use and contact your health care provider.
Do not use fennel tea simultaneously with other formulations of fennel, such as tablets, extracts or herbal blends, as combining these can increase the risk of a fennel overdose. An overdose of liquid fennel seed extract or drinking too much fennel tea can lead to itchiness, a rash or photodermatitis, an abnormal skin reaction to ultraviolet rays that causes your skin to become photosensitive, which means your skin is very sensitive to sunlight and more susceptible to sunburn. If you notice unusual skin changes, contact your health practitioner and stop using fennel.
Although small amounts of fennel are safe when derived from the fruit and seeds of the fennel plant, the oil from fennel seeds should be avoided. Fennel seed oil can be toxic and may cause seizures, nausea and respiratory problems, according to Herbs and Breastfeeding, an article by Ruth A. Laurence, M.D. Drinking large amounts of fennel tea can also trigger muscle spasms and, in rare cases, hallucinations, according to Bitterroot Restoration.
Problems for Women
Fennel contains phytoestrogens -- plant compounds that mimic the effects of estrogen in the body. Large quantities of fennel tea or herbal remedies containing fennel can act as a uterine stimulant, which is one reason why pregnant women should avoid fennel products. In folk medicine, fennel tea was used to stimulate lactation, but the effects of fennel on babies is unknown, so breastfeeding mothers should talk to their health care professional before drinking any fennel tea.