What is the injection and how does it work?
The injection releases the hormone progestogen into the body, which stops an egg cell being released from the ovaries (ovulation). Injections are needed every 12 weeks. The injection is over 99% effective.
What are the advantages?
- It is a good method of contraception for women who cannot use oestrogen hormone
- There is no need to think about contraception for as long as the injection works
- It does not interrupt sex
- It can be used when breast feeding
- It is not affected by other medicines
- May protect against cancer of the womb
What are the disadvantages?
- Periods may become irregular or stop
- Regular periods and fertility may take up to a year to return after stopping the injections
- There may be some side effects such as headaches, breast tenderness and acne
- Some women gain weight
- It does not protect against STIs
- The injection works for up to 12 weeks, the hormone cannot be removed from the body so any unwanted side effects continue during this time