St John’s Wort can make hormonal contraception less effective, with a real risk of unintended pregnancy. This is one of the most commonly missed interactions in either direction: people on the pill do not think a herbal supplement could affect it, and people buying the supplement are not asked what contraception they use.
It works by speeding up the liver enzymes that break down the contraceptive hormones, so less remains in your system. There is usually no warning sign. Breakthrough bleeding sometimes occurs, but effectiveness can be reduced without it.
Common side effects reported with this supplement or ingredient
On its own, mild: stomach upset, tiredness, restlessness, headache, and increased sensitivity to sunlight. See St John’s Wort side effects.
Possible interactions with medicines, chronic conditions or pregnancy
Methods that rely on hormones absorbed and circulated through the body can be affected, including the combined pill, the progestogen-only pill, the implant, the patch and the vaginal ring.
Methods less likely to be affected include the copper coil, which contains no hormones at all, and the hormonal intrauterine system, which acts mainly where it is placed rather than throughout the body. If you are considering St John’s Wort and contraception is a concern, this distinction is worth raising with a clinician, since it may change which method suits you.
The effect does not stop the moment you stop the supplement. Enzyme activity takes time to return to normal, so additional contraception may be advised for a period afterwards. Ask how long rather than assuming it is immediate.
See supplements that affect birth control and hormonal contraception side effects.
Who should speak to a healthcare professional before using it?
Anyone using hormonal contraception who is considering St John’s Wort, and anyone already taking both. Tell your contraception provider rather than your supplement seller, and mention it at your next contraception review even if you have since stopped.
If you are taking it for low mood, that is worth addressing properly rather than treating a symptom with a product that quietly undermines something else you rely on.
Dose, product-quality and stacking risks
Herbal products vary in strength, so the extent of the effect is unpredictable. Assume the interaction applies rather than hoping a particular product is weak enough not to matter.
St John’s Wort is also present inside some combination mood and stress formulas without being obvious on the front of the pack. Read the full ingredient list.
When to stop and get medical advice
If you have been taking both, use additional contraception such as condoms and speak to your contraception provider promptly. Do not simply stop the contraception.
If you think you may already be pregnant, take a test and seek advice. If you need emergency contraception, be aware that St John’s Wort can also reduce the effectiveness of the emergency pill, so mention it when you ask, since a different option may be recommended. See emergency contraceptive pill side effects.
Related supplement safety guides
- Supplement and medicine interactions
- St John’s Wort interactions
- Supplement side effects
- When to see a doctor about a supplement
- Report a supplement side effect
Medical Disclaimer: This content is for informational and educational purposes only and does not constitute medical diagnosis, prescription, or professional advice. Always read the patient information leaflet and consult a qualified doctor or pharmacist regarding any medicine or health concern.