The interaction between oral contraceptives and St John's Wort appears to be established. Its incidence is not known, but the limited poor quality evidence so far, suggests that breakthrough bleeding may be a problem. Pregnancy resulting from this interaction appears to be uncommon. It is not known who is most likely to be at risk of this interaction. There is very little information relating to the effect of SJW on other forms of hormonal contraception.

The recommendation of the CSM/MCA and the Faculty of Family Planning and Reproductive Health Care (FFPRHC) in the UK is that women taking oral contraceptives (both combined and progestogen-only pills) should either avoid St John's Wort or they should use an additional form of contraception.

The FFPRHC Clinical effectiveness unit also recommends that, if St John's Wort must be continued, the following general guidelines for the use of liver enzyme inducers with hormonal contraceptives should be followed:

• Women taking combined oral contraceptives should use an ethinylestradiol dose of at least 50 micrograms daily. The dose may be increased further above 50 micrograms if breakthrough bleeding occurs. Omitting or reducing the pill-free interval has not been shown to reduce therisk of ovulation with liver enzyme inducers. Additional non-hormonal methods of contraception, such as condoms, should also be used by patients using combined hormonal contraceptives, both when taking the liver enzyme inducers and for at least 4 weeks after stopping the drug. Alternatives to combined hormonal contraceptives should be considered with long-term use of liver enzyme inducers.
• The progestogen-only oral contraceptive is not recommended for use with liver enzyme inducers. Alternative methods of contraception are advised.

The FFPRHC Clinical effectiveness unit gives the following advice about alternative forms of hormonal contraception:

• The depot progestogen-only injection, copper and levonorgestrel-releasing intrauterine devices (IUD) do not appear to be affected by enzyme-inducing drugs, such as St John’s wort, and may be used as alternative contraceptive methods, particularly for women requiring hormonal contraception who are likely to be taking the enzyme inducer in the long-term, as these are unaffected by liver enzyme inducers.
• The combined contraceptive patch may be continued, however additional, non-hormonal methods of contraception, such as condoms, should also be used by patients using the combined contraceptive patch, both when taking the liver enzyme inducers and for at least 4 weeks after stopping the drug. Using more than one patch is not recommended.
• The progestogen-only implant may be continued with short courses of enzyme inducers. Additional non-hormonal methods of contraception, such as condoms, should also be used by patients using the progestogen-only implant, both when taking the liver enzyme inducers and for at least 4 weeks after stopping the drug. Alternatives to the progestogen-only implant should be considered with long-term use of liver enzyme inducers.
• The effectiveness of emergency hormonal contraceptive will be reduced in women taking liver enzyme inducers. The FFPRHC Clinical effectiveness unit states that there appears to be no good evidence on how to manage the interaction between emergency hormonal contraception and enzyme inducers such as St John's wort, but current clinical practice is to increase the contraceptive dose by approximately 50%.The British National Formulary recommends giving a single 3-mg dose of levonorgestrel, although this is unlicensed. A copper IUD may also be used as an effective alternative. In the UK, it is possible to buy the progestogen-only emergency hormonal contraception without a prescription; however, it has been advised that patients taking enzyme inducers should be referred to a doctor or family planning service.