The Injection

What is it?
The contraceptive injection protects you against pregnancy for eight weeks or 12 weeks, depending on the type you use.

There are two versions: Depo-Provera, which lasts for 12 weeks, and Noristerat, which lasts for eight weeks. The most popular is Depo-Provera. 

How does it 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 cannot implant itself there. In some women, the injection stops ovulation (the release of an egg).

How effective is it?
If used correctly it is more than 99% effective. This means that less 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 do not 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 Pill every day.
• It can be useful for women who cannot use contraception that contains oestrogen.
• It is not affected by medication.
• It 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 works for eight or 12 weeks. It cannot be removed from your body, so if you have side effects, they will persist during these weeks, and for some time afterwards.
• Your periods may become more irregular or longer, or stop altogether (amenorrhoea). Amenorrhoea is a common effect of the contraceptive injection. It is not harmful, but you may want to take it into consideration.
• There is treatment available if your bleeding is heavy or prolonged. Talk to your doctor or nurse about this.
• It can take up to one year for your fertility level 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 is not a problem for most women because the bone replaces itself when you stop the injection, and it does not 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 will help to protect yourself against sexually transmitted infections (STIs).