How effective is it?
Over 99 per cent effective if taken according to instructions. Less than one woman in 100 will get pregnant in a year.
How does it work?
Contains the hormone progestogen, which thickens cervical mucus to prevent sperm reaching an egg. In some cycles it stops ovulation.
What are the advantages?
- Can be used by women who cannot use oestrogen.
- Can be used by women who smoke and are over 35.
- May make periods stop, become lighter or less frequent.
What are the disadvantages?
- Periods can become irregular and sometimes more frequent.
- May be temporary side-effects such as acne, weight change and headaches.
- May get ovarian cysts.
Anything else I should know?
- It needs to be taken at the same time each day.
- Not effective if taken over three hours late (12 hours for Cerazette) or after vomiting or severe, long-lasting diarrhoea.
- Some medicines may make it less effective.