The contraceptive injection is used to prevent pregnancy. It contains a hormone and lasts for up to 3 months.
What is the contraceptive injection?
The injection contains a synthetic version of the hormone progestogen, called depot medroxyprogesterone acetate or DMPA.
It is given into your buttock or the upper arm, and over the next 12 weeks the DMPA is slowly released into your bloodstream.
The injection is usually given during the first 5 days of the menstrual cycle, so it can start working straight away. If you have the injection at some other time in your cycle, it can take up to 7 days to start working.
Types of contraceptive injection
How does the contraceptive injection work?
The injected hormone stops your body from releasing eggs from your ovaries.
The injection also thickens the fluid at the entrance to the uterus (womb), which stops sperm from entering. It also thins the lining of the uterus, making it difficult for a fertilised egg to attach and develop.
How well does the contraceptive injection work?
The contraceptive injection is fairly effective if used properly. If 100 women were to use it for 1 year, however, between 1 and 6 are still likely to become pregnant.
The contraceptive injection won't protect you from sexually-transmitted infections (STIs). You should use condoms for additional protection against STIs, although even condoms won't protect you from every type of infection.
Advantages and disadvantages of the contraceptive injection
The main advantages are that:
- you only need to have the injection once every 3 months
- it is safe for use by most women, including those who are breastfeeding.
The main disadvantages are that:
- it changes the pattern of your periods - they might become more frequent or longer lasting, then stop completely
- if you stop using it, it can take a while to get pregnant
- it can cause side effects such as weight gain, moodiness, headaches and acne
- it might cause bone thinning if used for a long time.
If you miss an injection, or stop having the injections
You need to have the injection every 12 weeks if you want to prevent pregnancy. It can be given up to 2 weeks late, but if you wait any longer than that, it's best to use condoms until the injection has had time to start working again.
When you stop getting the injection, it can take several months for your periods to return to normal, and even longer to become pregnant.
For more information, see Family Planning NSW.
Last reviewed: February 2017