NHS ChoicesMedical Reference
The progestogen-only contraceptive pill is taken by women to prevent pregnancy.
It contains progestogen, a synthetic (artificial) version of the hormone progesterone that women produce naturally in their ovaries.
The progestogen-only pill differs from the combined contraceptive pill, which contains both female sex hormones oestrogen and progestogen. This makes the progestogen-only pill an option for women who cannot take the combined contraceptive pill, such as those over the age of 35 or those who smoke.
One pack of the progestogen-only pill contains 28 pills. One pill is taken every day of the menstrual cycle.
How effective is it?
When taken correctly, the progestogen-only pill is more than 99% effective at preventing pregnancy. This means that less than one woman in every 100 will get pregnant in a year.
How the progestogen-only pill works
The progestogen-only pill works in two ways:
- it thickens the mucus in the neck of the womb, so it is harder for sperm to penetrate into the womb and reach an egg
- it thins the lining of the womb, so there is less chance of a fertilised egg implanting into the womb and being able to grow
Sometimes, the progestogen-only pill may also prevent ovulation (the release of an egg from your ovaries each month).
Types of progestogen-only pill
There are two different types of progestogen-only pill, which must be taken at different times of the day:
- The three-hour progestogen-only pill must be taken within three hours of the same time each day. Examples are Femulen, Micronor, Norgeston and Noriday.
- The 12-hour progestogen-only pill (Cerazette) must be taken within 12 hours of the same time each day. It is less commonly used than the three-hour pill.