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Medicines, supplements and your contraception

Most antibiotics are fine. A few medicines are not. Here is what to check.

Contraception5 min readDeep dive

Written by the Splash teamSources checked

On this page 6 sections
  1. Quick answer
  2. Antibiotics
  3. Medicines that can reduce hormonal contraception
  4. Lamotrigine
  5. Weight-loss and diabetes injections (GLP-1 medicines)
  6. Sources

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 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 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)

If you use one of these, a copper coil, hormonal coil (IUS) or the injection are not affected, so they are often recommended instead. The implant and the 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 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, 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).

Quick quizWhich of these is known to make the combined pill less reliable?
  1. A short course of amoxicillin
  2. St John’s wort
  3. Paracetamol
Show the answer

B. 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
  2. NHS – How to use the vaginal ring
  3. FSRH/CoSRH – Clinical guidelines (progestogen-only pills; emergency contraception)
  4. MHRA – GLP-1 medicines for weight loss and diabetes: what you need to know

Written by the Splash teamSources checked

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). How we write and check articles.

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