How reliable is it?
With careful use, one woman in 100 will get pregnant in a year. With less careful use, four or more women in 100 will get pregnant in a year.
How it works
The hormone progestogen, taken at the same time each day, causes changes making it difficult for sperm to enter the womb or for the womb to accept a fertilised egg. In some women it prevents ovulation.
Does not interrupt sex.
Useful for older women who smoke and women who cannot use the combined pill.
Can be used when breastfeeding.
May be temporary minor side effects.
Periods may be irregular, with some bleeding in between or be missed.
May be less effective in women who weigh over 70kg (11 stone).
Does not protect against sexually transmitted infections.
Not reliable if taken over three hours late or after vomiting or severe diarrhoea, unless an extra method is used.
Some drugs may stop the pill working - a doctor or a pharmacist can advise.