A herbal medicine usually taken by women for menstrual disorders may interact with the contraceptive pill and has been linked with at least one unintended pregnancy, the TGA has warned.

In a safety advisory, the regulator says it has received a report of an unintended pregnancy following concurrent use of Vitex agnus castus with norethisterone, a progesterone-only contraceptive pill.

One other similar case has been reported overseas with the herb — also known as Chaste Tree, Chasteberry and Monk’s Pepper — and even though studies are limited, the potential for interaction between the two has been recognised internationally, the TGA says.

“Health professionals should be aware that some studies indicate Vitex agnus-castus may bind [oestrogen] and dopamine receptors which suggests the potential for interaction with medications that have [oestrogenic] and/or dopaminergic actions,” the TGA said in its safety advisory issued on Friday.