Yes. St. John’s wort can make emergency contraceptive pills less effective, including pills containing levonorgestrel and ulipristal acetate. It speeds up the body’s processing of these medicines, lowering the amount available to work. The interaction may still matter for up to four weeks after you stop the herb. Ask a pharmacist or clinician promptly about the best option, especially if you had unprotected sex recently.
How does St. John's wort affect emergency contraception?
St. John’s wort is an herbal supplement commonly used for mood-related concerns, including depression. Although it is available without a prescription in many places, it can interact with medicines, including hormonal contraceptives.
The herb can increase the activity of certain liver enzymes, particularly CYP3A4, which help the body break down medicines. This can lower the amount of some emergency contraceptive medicines in the bloodstream and may reduce their ability to prevent pregnancy. The interaction does not mean that emergency contraception will definitely fail, but it makes choosing the right method particularly important.
The UK Medicines and Healthcare products Regulatory Agency (MHRA) specifically identifies St. John’s wort as a herbal product that can reduce blood levels of levonorgestrel and potentially lower the effectiveness of levonorgestrel emergency contraception. The MHRA also warns that the effects of enzyme-inducing medicines can persist for up to four weeks after stopping them. Read the MHRA guidance.
Which emergency contraceptive pills can interact with St. John's wort?
Levonorgestrel emergency contraception
Levonorgestrel is a hormone used in emergency contraceptive pills, including Plan B One-Step in the United States and Levonelle in the United Kingdom. It works mainly by delaying or preventing ovulation, the release of an egg from an ovary.
St. John’s wort may cause the body to break down levonorgestrel more quickly, reducing the amount available to have its intended effect. As a result, a standard dose may not provide the expected level of protection when the herb is being taken or has been used recently. This interaction matters even if the herbal supplement is not taken at exactly the same time as the emergency contraceptive pill.
Ulipristal acetate emergency contraception
Ulipristal acetate, sold under brand names such as ella and ellaOne in different countries, is another emergency contraceptive pill. It can be used for up to 120 hours, or five days, after unprotected sex.
The U.S. Food and Drug Administration’s prescribing information for ella warns that St. John’s wort can lower the medicine’s concentration in the bloodstream and may reduce its effectiveness. It advises avoiding the combination with products that induce the CYP3A4 enzyme. Because of this interaction, ulipristal acetate is generally not recommended for people who are currently taking enzyme-inducing medicines or who have stopped them recently. See the prescribing information for ella.
What should you do if you use St. John's wort and need emergency contraception?
Seek advice from a pharmacist, doctor, or sexual health service as soon as possible. Emergency contraception works best when used promptly, so do not delay seeking help while trying to determine which pill is suitable.
Tell the healthcare professional when you last had unprotected sex, which emergency contraceptive pill you have taken or are considering, and whether you currently use St. John’s wort or stopped it recently. Include the date you stopped the supplement and details of any other prescription medicines, over-the-counter products, or herbal remedies you take.
Could a copper IUD be a better option?
A copper intrauterine device (IUD), sometimes called a copper coil, is a non-hormonal form of emergency contraception. It is inserted into the uterus by a trained healthcare professional and is not affected by the enzyme-inducing action of St. John’s wort.
The World Health Organization (WHO) identifies the copper IUD as the most effective form of emergency contraception. When inserted within 120 hours, or five days, after unprotected sex, it is more than 99% effective at preventing pregnancy. It can also provide ongoing contraception after it has been fitted. Whether it is suitable depends on individual circumstances and clinical assessment. Read the WHO guidance on emergency contraception.
Can you take a different dose of levonorgestrel?
In UK guidance, when someone has used an enzyme-inducing medicine within the previous four weeks and a copper IUD is not an option, a healthcare professional may advise a double dose of levonorgestrel emergency contraception, increasing the usual 1.5 mg dose to 3 mg. Ulipristal acetate is not recommended in this situation.
The Faculty of Sexual and Reproductive Healthcare (FSRH) includes this approach in its emergency contraception guidance. However, recommendations and product instructions can differ between countries, and the best option depends on the timing of sex, medicines used, and individual circumstances. Do not take extra tablets or combine emergency contraceptive pills without professional advice. Review the FSRH emergency contraception guideline.
Does timing matter if you have already taken an emergency contraceptive pill?
Yes. If you have already taken an emergency contraceptive pill while using St. John’s wort, contact a pharmacist or clinician promptly. Do not assume the pill has failed, but explain the interaction so you can receive advice about whether another emergency contraception option is appropriate.
The NHS explains that levonorgestrel emergency contraception should generally be taken within 72 hours of unprotected sex, while ulipristal acetate can be used within 120 hours. A copper IUD may also be fitted within five days. These time limits and the interaction with St. John’s wort make prompt assessment important, especially if several days have passed. See the NHS guidance on when to take emergency contraception.
Because the interaction can reduce the effectiveness of oral emergency contraception, ask the healthcare professional whether and when you should take a pregnancy test. Follow-up testing is particularly important when an enzyme-inducing medicine may have reduced the effectiveness of levonorgestrel.
Can you continue taking St. John's wort after emergency contraception?
Discuss this with the healthcare professional who advises you about emergency contraception. The timing of St. John’s wort use matters because its effects on medicine-processing enzymes may continue after you stop taking it. Simply separating the supplement and the emergency contraceptive pill by a few hours should not be assumed to prevent the interaction.
If you use St. John’s wort regularly, also tell the professional who recommends or prescribes your ongoing contraception. Some hormonal contraceptives may be affected by enzyme-inducing medicines as well. Reviewing your medicines and contraceptive needs together can help identify a suitable option for both emergency and ongoing pregnancy prevention.