How the combined pill works

The pill uses copies of 2 natural hormones – oestrogen and progesterone – to prevent pregnancy.

When you digest the pill, these hormones get absorbed into your blood and change the hormone levels in your body.

The change in hormone levels caused by the pill has the following effects: 

  • it stops eggs from developing and being released (ovulation), which means there’s no egg to be fertilised

  • it thickens the fluid released by the cervix (cervical mucus), so sperm cannot travel into the womb

  • it thins the lining of the womb - a fertilised egg can’t implant in a womb with a thinned lining. This is a backup measure as most people won’t produce an egg at all.

How your body breaks down the pill

  1. The pill is digested in your stomach.  

  2. Your bloodstream takes the pill all over your body, changing your hormone levels and leading to the other health benefits, risks and side effects of the pill.

  3. Your liver changes the hormones from the pill so they’re ready to be expelled from the body, which is why it’s not recommended if you have severe liver problems.

  4. Hormones are lost from your body through your bowel – so you have to keep taking it every day to keep hormones at the level that stops you from ovulating.

How the pill affects your ovaries and uterus (womb)

Around the time of ovulation, the fluid that’s produced by your cervix (known as cervical mucus) gets slippery, making it easier for sperm to enter the womb. At the same time, the lining of the womb gets thicker so it’s easier for an egg to implant.

The hormones in the pill cause changes in the womb and ovaries. No egg is released, the cervical mucus is thicker and the womb lining is thinner.

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