Side Effects of Fennel Seed Tea

Fennel, a dill-like member of the carrot family, is widely known for its licorice-like flavor. Like anise, star-anise and licorice, fennel seed contains anethole-- a natural medicinal compound chemically similar to estrogen. Fennel seed's multifaceted effect on the human body has earned it a reputation as a virtual panacea for women's health. Modern herbalists recommend fennel seed as a treatment for dozens of conditions, ranging from low breast milk supply to colic and menopause.

Unfortunately, like all effective remedies, fennel may be associated with certain risks. The following fennel seed side effects are most likely to occur after prolonged or improper use.

Premature Breast Development

Fennel tea is a popular, traditional remedy for colic in infants, but it shouldn't be used for extended peridos of time. One of the side effects of fennel seed is thelarche, or premature breast development, according to a 2008 report published in the Journal of Pediatric Surgery. Several newborns taking large quantities of fennel seed tea have developed breasts before age two.

Neurotoxicity

The seeds, leaves, roots and stems of the fennel plant are ultimately nontoxic, but fennel seed oil contains a potent concentration of volatile oils, which may be toxic. Lactation expet Kelly Bonyata warns that even small doses of fennel oil may cause seizures and respiratory problems. There is one case report of a baby developing brain damage while his mother was drinking fennel seed tea, but it's not clear if the fennel seed tea was the cause.

Drug Interactions

People taking drugs to treat epilepsy, including gabapentin and phenytoin, should avoid fennel seed. Seizures are a common side effect of fennel seed for people taking antiseizure medications. Other drug interactions are possible, but none have been documented.

Allergic Reaction

Almost all drugs, compounds and herbs can cause an allergic reaction. Some of the common side effects of fennel seed tea include allergic reactions like dermatitis, hives, wheezing and gastrointestinal problems. Rarely, fennel may trigger anaphylaxis, a life-threatening allergic reaction.