Published: 6 June 2014

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St John's wort and implanted hormonal contraceptives

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Prescriber Update 35(2)
6 June 2014

St John's wort (Hypericum perforatum) is a herbal medicine traditionally used to relieve low mood. The interaction between St John's wort and contraceptives was highlighted by Medsafe in 2000¹.

In addition to potentially interacting with oral hormonal contraceptives, St John's wort has now been noted to interact with implanted hormonal contraceptives.

There have been overseas reports of unplanned pregnancies associated with use of St John's wort in women who have implanted hormonal contraceptives. Prescribers should advise women using any hormonal contraceptives for pregnancy prevention to avoid herbal products containing St John's wort or to use an additional form of contraception when they are using such products^{2, 3}.

In New Zealand although there have not been any reports of pregnancy in women using hormonal contraceptives and St John's wort concomitantly, there have been three reports of breakthrough bleeding.

Prescribers are encouraged to report suspected adverse events related to complementary medicines to CARM. Doctors are encouraged to ask patients explicitly about complementary medicine use, as such use may not be volunteered when patients are asked about the medications they are using.

References

1. Medsafe. 2001.  Interactions with St John's wort (Hypericum perforatum) preparations. Prescriber Update, 20: 42-48.
2. MHRA. St John's wort: interaction with hormonal contraceptives, including implants - reduced contraceptive effect. Drug Safety Update 7: A2, No. 8, 13 Mar 2014. Available from: URL: www.mhra.gov.uk/home/groups/dsu/documents/publication/con392897.pdf
3. Stockley IH. 2002. Stockley's Drug Interactions. London: Pharmaceutical Press.