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Safety advisory - potential for interaction with oral contraceptives
Vitex agnus-castus is a herb, also known as Chaste Tree, Chasteberry and Monk's Pepper. It is mostly marketed for menstrual disorders, including symptoms of premenstrual syndrome and/or menopause, as well as for acne.
Vitex agnus-castus is permitted for use in listed medicines in Australia. Listed medicines are identified by an 'AUST L' number on the label. Listed medicines that contain Vitex agnus-castus are available from a range of suppliers including through pharmacies, health food stores and supermarkets.
The TGA has received one report of an unintended pregnancy following concurrent use of Vitex agnus-castus and norethisterone, a progesterone-only oral contraceptive pill. One other similar case has also been reported internationally.
There are limited studies into the interactions between Vitex agnus-castus and oral contraceptives. However, the potential for such an interaction is recognised internationally. Health Canada and the European Medicines Agency (EMA) advise consumers to consult a health practitioner prior to using Vitex agnus-castus-containing products if they are taking hormone-containing medications such as progesterone preparations, oral contraceptives or hormone replacement therapy.
Information for consumers
Consumers taking an oral contraceptive to prevent pregnancy should be aware that Vitex agnus-castus may interfere with how well the contraceptive works.
Consumers taking medicines with contraceptive, hormonal and/or dopaminergic actions should consult their health professional prior to combined use with Vitex agnus-castus.
Information for health professionals
Health professionals should be aware that some studies indicate Vitex agnus-castus may bind estrogen1 and dopamine receptors2, which suggests the potential for interaction with medications that have estrogenic and/or dopaminergic actions.
Combined use with certain medicines, including oral contraceptives and other medicines with hormonal and/or dopaminergic actions, may result in decreased efficacy or additive effects, although there is limited evidence to verify the extent of these effects.
Information for sponsors
Sponsors should be aware of the potential for Vitex agnus-castus to interact with oral contraceptives and other medicines, and should consider appropriate risk communication strategies to inform consumers. The TGA is currently considering label warning requirements for Vitex agnus-castus when used in listed medicines.
Sponsors are also reminded of their obligation to report all serious adverse events to the TGA within required timeframes.
Consumers and health professionals are encouraged to report problems with medicines or vaccines. Your report will contribute to the TGA's monitoring of these products.
The TGA cannot give advice about an individual's medical condition. You are strongly encouraged to talk with a health professional if you are concerned about a possible adverse event associated with a medicine or vaccine.
1Liu, J, et al (2001). Evaluation of Estrogenic Activity of Plant Extracts for the Potential Treatment of Menopausal Symptoms. Journal of Agricultural and Food Chemistry, 49(5): 2472-2479.
2Laboratory testing for activity, potency or efficacy is not equivalent to clinical safety and efficacy studies, which are evaluated as part of the application to register therapeutic goods on the ARTG