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St John's Wort Found To Reduce The Effectiveness Of Emergency Contraception

Emergency contraception

The emergency contraceptive levonorgestrel is common taken with three days of unprotected sex. Addyvanich/Shutterstock

Commonly found in a variety of medicines, from those used to treat HIV to fungal infections, St John’s wort is very useful, but it has been found to interfere with a particular emergency contraceptive pill prescribed by doctors usually taken after unprotected sex, or when usual contraceptives fail.

The contraceptive in question is a drug known as levonorgestrel, an emergency pill that can be taken within three days after unprotected sex in order to prevent unwanted pregnancies. But now researchers have found that ingredients in other unrelated drugs, such as St John's wort, can interact with levonorgestrel and make it significantly less effective.


The Medicines and Healthcare products Regulatory Agency (MHRA) has issued an information sheet for those who may be affected by the new findings. They recommend that anyone taking any drugs that contain St John’s wort as an ingredient to tell your doctor if you’ve been using them within the last four weeks. These drugs include those prescribed for epilepsy, tuberculosis, HIV, fungal infections, or other herbal remedies that might contain extracts of the plant.  

St John’s wort (Hypericum perforatum) is a plant found across much of Europe, Asia, and North America, and contains an active compound called hypericin. The plant is commonly used as a herbal remedy to treat depression, and a Cochrane review that assessed 29 randomized controlled trials of the plant found that it was better than a placebo at treating major depression, being as effective as standard antidepressants, and showing fewer side effects.

The MHRA recommend that if a woman is taking any of the drugs implicated, and also requires emergency contraception, then they should consider other types, such as the coil. This is a copper intrauterine device inserted into the womb, and is not known to interfere with other medications. Alternatively, considering that St John’s wort makes levonorgestrel less effective, they have also suggested that people can double their dose, which should be taken at the same time.

“Our new patient information sheet provides information on what types of medicines could interfere with how the emergency contraceptive works,” explained Dr Sarah Branch, the deputy director of MHRA’s Vigilance and Risk Management of Medicines Division, to BBC News. “It tells women what steps they need to take to ensure they receive the correct dose. The earlier that emergency contraception is taken after unprotected intercourse, the better it works.”


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  • contraception,

  • drugs,

  • the pill,

  • emergency contraception,

  • St John's wort