Fennel refers to a flavoring obtained from the fruit of Foeniculum vulgare. Fennel oil is used in perfumes.
Foeniculum vulgare has been used as a folk medicine for its estrogenic properties. Ferula communis (giant fennel) contains a potent anticoagulant and induces severe haemorrhagic diathesis in grazing ewes, or similar changes in utero in lambs.
These and other teratogenic changes have been seen in babies from mothers receiving the anticoagulant warfarin during pregnancy. The reproductive toxicity of plant estrogens in humans has not been established; however, adverse fertility effects in animals suggest that some of these agents might have clinically relevant fertility effects on humans.
You should never use an herb without first discussing it with your doctor.