# Medicines, supplements and your contraception > Most antibiotics are fine. A few medicines are not. Here is what to check. Category: Contraception · 5 min read · Written by the Splash team · Sources checked October 2026 URL: https://splash.care/learn/contraception/medicines-and-contraception ## Quick answer - Most antibiotics do not affect the pill, patch or ring. Rifampicin and rifabutin do. - Some epilepsy, TB and HIV medicines and St John’s wort can reduce hormonal methods. - Coils and the injection are not affected by these. - Check the latest MHRA advice if you use weight-loss injections such as Mounjaro. Many people worry that every antibiotic cancels out the pill. The good news is that most do not. But a small number of medicines and herbal remedies really can make some [contraception](https://splash.care/learn/contraception/methods-overview) work less well, so it is worth checking each time you start something new. ## Antibiotics Most common antibiotics do **not** make the pill, patch or ring less effective. The exceptions are rifampicin and rifabutin (used for TB and some other infections), which are strong “enzyme-inducers”. Being sick or having severe diarrhoea because of an illness can also stop the pill working, whatever the cause. ## Medicines that can reduce hormonal contraception The NHS asks you to check with a [doctor](https://splash.care/learn/conditions/talk-to-your-doctor) or pharmacist before using the pill or ring if you take medicine for: - Epilepsy (some, such as carbamazepine, phenytoin and topiramate) - TB (rifampicin, rifabutin) - HIV (some HIV medicines) - Griseofulvin (an antifungal) - Bosentan (for high blood pressure in the lungs) - St John’s wort (a herbal remedy for [low mood](https://splash.care/learn/mind-mood/why-mood-shifts)) If you use one of these, a copper coil, hormonal coil ([IUS](https://splash.care/learn/glossary/ius)) or the injection are not affected, so they are often recommended instead. The implant and the [progestogen](https://splash.care/learn/glossary/progestogen)-only pill can be affected. ## Lamotrigine Lamotrigine (used for epilepsy and bipolar disorder) is a bit different. It is not an enzyme-inducer, but the [oestrogen](https://splash.care/learn/glossary/oestrogen) in combined pills, patches and rings can lower its levels in your blood, which can affect seizure control, and levels can rise in the break. Ask your prescriber before starting or stopping any combined method. ## Weight-loss and diabetes injections (GLP-1 medicines) Check the latest MHRA advice if you are on, or starting, a GLP-1 medicine. If you take the pill with Mounjaro (tirzepatide), add a barrier method such as condoms for 4 weeks after you start and for 4 weeks after every dose increase, or switch to a non-oral method like the coil or implant. These medicines should not be used in [pregnancy](https://splash.care/learn/fertility-ttc/early-pregnancy-signs), so effective contraception matters, and they need to be stopped for a time before you try to conceive (at least 2 months for semaglutide, at least 1 month for tirzepatide). > Emergency contraception can be affected too. If you take an enzyme-inducing medicine, the levonorgestrel pill is usually given as a double dose, and the copper coil is not affected. Always tell the pharmacist or nurse every medicine and herbal remedy you take. > **Splash says:** make “mention my contraception” part of every new prescription. Pharmacists check this all the time, and it takes ten seconds. ### When to see a doctor If you have had unprotected sex, or you are not sure whether your medicine affects your contraception, speak to a pharmacist, sexual health clinic, GP or call 111. You may need condoms or emergency contraception. **Quick quiz:** Which of these is known to make the combined pill less reliable? 1. A short course of amoxicillin 2. St John’s wort 3. Paracetamol Answer: St John’s wort. St John’s wort speeds up how your body clears hormones. Most common antibiotics and paracetamol do not affect the pill. ## Sources 1. [NHS – How to take the combined pill](https://www.nhs.uk/contraception/methods-of-contraception/combined-pill/how-to-take-it/) 2. [NHS – How to use the vaginal ring](https://www.nhs.uk/contraception/methods-of-contraception/vaginal-ring/how-to-use-it/) 3. [FSRH/CoSRH – Clinical guidelines (progestogen-only pills; emergency contraception)](https://www.cosrh.org/Public/Public/Standards-and-Guidelines.aspx) 4. [MHRA – GLP-1 medicines for weight loss and diabetes: what you need to know](https://www.gov.uk/government/publications/glp-1-medicines-for-weight-loss-and-diabetes-what-you-need-to-know/glp-1-medicines-for-weight-loss-and-diabetes-what-you-need-to-know) This is general information, not medical advice. Splash can’t diagnose. If you’re worried, talk to a GP, pharmacist or sexual health clinic. In an emergency call 999 (UK) or 911 (US).