The contraceptive injection protects you against pregnancy for eight weeks or 12 weeks, depending on the type you use. Find out how it works, side effects and where you can get it.
A woman can get pregnant if a man’s sperm reaches one of her eggs (ova). Contraception tries to stop this happening by keeping the egg and sperm apart or by stopping egg production. One method of contraception is the injection.
There are two versions of the contraceptive injection: Depo-Provera, which lasts for 12 weeks, and Noristerat, which lasts for eight weeks. The most popular is Depo-Provera.
How does the contraceptive injection work?
The injection contains progestogen. Progestogen thickens the mucus in the cervix, which stops sperm reaching an egg. It also thins the lining of the womb so that an egg can't implant itself there. In some women, the injection stops ovulation (the release of an egg).
How effective is the injection?
If used correctly it's more than 99% effective. This means that fewer than one woman in 100 who uses the injection will become pregnant in a year.
Added benefits?
- The injection lasts for eight weeks or 12 weeks (depending on the type), so you don't have to think about contraception every day or every time you have sex.
- It can be useful for women who might forget to take the contraceptive pill every day.
- It can be useful for women who can't use contraception that contains oestrogen.
- It's not affected by medication.
- The contraceptive injection may provide some protection against cancer of the womb and pelvic inflammatory disease.
What else should I know?
- Side effects can include weight gain, headaches, mood swings, breast tenderness and irregular bleeding.
- The injection can't be removed from your body, so if you have side effects they'll last as long as the injection (eight or 12 weeks) and for some time afterwards.
- Your periods may become more irregular or longer, or stop altogether (amenorrhoea). Having no periods is a common effect of the contraceptive injection. It's not harmful, but you may want to take it into consideration.
- Treatment is available if your bleeding is heavy or longer than normal – talk to your doctor or nurse about this.
- It can take up to one year for your fertility to return to normal after the injection wears off, so it may not be suitable if you want to have a baby in the near future.
- Using Depo-Provera affects your natural oestrogen levels, which can cause thinning of the bones. This isn't a problem for most women because the bone replaces itself when you stop the injection, and it doesn't appear to cause any long-term problems.
Thinning of the bones may be a problem for women who already have risk factors for osteoporosis (such as low oestrogen, or a family history of osteoporosis). It may also be a concern for women under 19 because the body is still making bone at this age. Women under 19 may use Depo-Provera, but only after careful evaluation by a doctor.
By using condoms as well as the injection, you'll help to protect yourself against sexually transmitted infections (STIs).
Further information
Find out about the 15 methods of contraception
Find out about losing weight
When can I use contraception again after having a baby?
What infections can I catch through oral sex?
Where can I go for help and advice on sexual health?