How does the contraceptive pill work?

How the pill protects you from pregnancy


The contraceptive pill is a popular method of hormonal contraception used by millions of women in the UK. There are two different types; the combined pill and the progesterone-only mini pill. Both of these types contain versions of the progesterone hormone, and the combined pill has oestrogen as well as progesterone. Oestrogen and progesterone are hormones that are produced naturally in a woman's body and regulate the menstrual cycle. 

The combined pill 

When you take the combined pill, synthetic versions of oestrogen and progesterone hormones are released into the body. This works to prevent pregnancy in three ways:

  • Stopping ovulation - This is where your ovaries release an egg into the fallopian tube which travels into the womb ready to be fertilised. The combined pill overrides your natural cycle so that this doesn't happen 
  • Thickening the cervical mucus- the hormones cause the mucus that surrounds the cervix to thicken which makes it harder for sperm to get through 
  • Thinning the womb lining- during your natural cycle, the lining of the womb thickens after ovulation to prepare itself for a fertilised egg. Taking the pill reduces this so that should the previous two steps fail, a fertilised egg will not be able to attach itself to the uterine wall 

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The mini (progesterone only) pill 

The mini pill works in a similar way but does not entirely override your menstrual cycle like the combined pill. It is thought that the mini pill will prevent ovulation, but some women who take it may continue to ovulate. It does have the same effect on thickening the cervical mucus and thinning the womb lining. It is just as effective as the combined pill at preventing pregnancy. 

How effective is the pill? 

Both the combined pill and the mini pill are over 99% effective when they're taken correctly. This means taking the pills on time every day, starting a new pack on time, using additional contraception if you've missed pills or vomited and being aware of medications that might interfere with the way your contraception works. 

How do I take it? 

You'll start taking the pill on the first day of your period, which means you'll be protected against pregnancy right away. Follow the days of the week, or arrows, printed on your pill strip which tell you the order to take them in. Most forms of the combined pill are taken every day for 21 days before having a 7-day break until you start your next one. The mini-pill is taken every day without a break and must be taken at the same time each day or its effectiveness can be impacted. 

View our full range of contraceptive pills.


NHS > The Combined Pill
NHS > The Progestogen-only Pill

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