The injection is sometimes called 'Depo'
How do they work?
The main way it works is by stopping the ovaries releasing an egg (ovulation) each month. It also:
- Thickens the mucus in the cervix, making it difficult for sperm to travel to reach an egg.
- Makes the lining of the womb thinner so it's less likely to accept a fertilised egg (this means you may not have any periods).
How long do they last?
- You should have an injection every 11 - 12 weeks. You will be told when to come back for your next injection.
How is it effective?
- As long as you attend on time for injections it's more than 99% effective. This means that using this method, fewer than one woman in 100 will get pregnant in a year.
- You don’t have to think about contraception for as long as the injection lasts.
- It's not affected by other medicine.
- It may reduce heavy painful periods and help with premenstrual symptoms for some women.
- You can use it if you can't use oestrogens like those in the combined pill.
- You can use it if you are breastfeeding
- After stopping, your periods and normal fertility may take some time to return.
- You may experience irregular bleeding which may continue for some months after you stop the injection.
- Some women report having headaches, acne, mood changes and breast tenderness.
- The injection lasts for the full 11 or 12 weeks after you have it, so if you have side effects they will continue during this time and for some time afterwards - there is no antidote.