The contraceptive injection

You can prevent pregnancy with an injection every two or three months. This fpa factsheet explains how this method works and whether it could be suitable for you.

What is it?

The contraceptive injection contains the hormone progestogen. There are two types of injection:

Depo-Provera provides contraception for three months (12 weeks)
Noristerat provides contraception for two months (eight weeks)

Depo-Provera is the most used injectable method in the UK. Injectable contraception is a long-acting method of contraception.

How does it 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 reach an egg
Makes the lining of the womb thinner so it's less likely to accept a fertilised egg

Myth: The injection will make you infertile
Fact: Not true - but normal fertility can take some time to return after using Depo-Provera
Myth: You can only use it for two years
Fact: Not true - it can be used for longer providing you do not have any risk factors for osteoporosis (being over 45, poor diet, low exercise or family history of osteoporosis)

How reliable is it?

It's more than 99 per cent effective. This means that using this method, fewer than one woman in 100 will get pregnant in a year. All long-acting reversible methods are very effective because while they're being used you don't have to remember to take or use contraception.

How do you use it?

The hormone is injected into a muscle, usually in your bottom. Depo-Provera can also sometimes be given in the leg or arm. The injection can be started up to and including the fifth day of your period. If started at any other time, additional contraception has to be used for seven days.

Advantages:

Very effective
Doesn’t interrupt sex
You can use it if you cannot use estrogens or are breastfeeding
May reduce heavy painful periods and help with premenstrual symptoms for some women
May give you some protection against cancer of the womb
May give you some protection against pelvic inflammatory disease
Not affected by other medicines

Disadvantages:

Your periods may change in a way that is not acceptable to you, or they may stop
Irregular bleeding may continue for some months after you stop the injection
You may put on weight when you use Depo-Provera
Some women report having headaches, acne, mood changes and breast tenderness
The injection lasts for eight or 12 weeks, so if you have side-effects they will continue during this time and for some time afterwards
Your periods and normal fertility may take some time to return - more than a year for some women

Can anyone use it?

Most women can have the contraception injection, but it may be unsuitable if you:

Think you might already be pregnant
Want a baby within the next year
Don't want your periods to change
Have thrombosis, heart or circulatory disease
Have active liver disease
Have breast cancer now or within the past five years
Have migraines with aura
Have diabetes with complications or have had diabetes for more than 20 years
Have risk factors for osteoporosis

Other things to consider

Once you've had the injection you don't need to think about it until it needs replacing
You don't need a cervical screening test or internal examination to have the injection
It doesn't protect you against sexually transmitted infections
Depo-Provera affects your normal estrogen level, which may cause thinning of the bones, but once you stop any risk is reversed - women aged under 18 and over 45 will be carefully counselled about this