The injection provides two to three months contraceptive protection depending on the type you use. It contains the hormone progestin and it works by slowly releasing a hormone that stops the body producing an egg each month. The hormone also makes it harder for the man’s sperm to get into the womb.
The injection is usually given in the arm, thigh or buttock by a trained provider. It only takes a few minutes to have the injection. It can take up to seven days before the injection starts to work if you have not previously used a contraceptive. You can use a condom for those 7 days.
Note: Condoms are the only contraceptive methods which also protect against sexually transmitted infections. To ensure protection from both pregnancy and infection, we recommend "dual protection". This means using a contraceptive method of your choice to prevent pregnancy in addition to a male or female condom.
How good is the injection at preventing a pregnancy?
- The injection works very well at preventing a pregnancy. If one hundred women used the injection for a year and carried on with their normal sex life then only one of those women would fall pregnant during that period.
- It is difficult for some women to remember to get their injections on time. With typical use, about three women out of 100 would fall pregnant.
What are the advantages of the injection?
- Depending on the injection it can last up to either two or three months. After each two or three months you will need to have another injection.
- It can help to reduce heavy periods.
- It does not interrupt sex.
- It is discreet – no one can see that you are using it.
- You can start it straight after an abortion.
What are the disadvantages of the injection?
- Once you have had the injection it cannot be removed. You will have to wait the two or three months for its effects to end, even if you decide you don’t want it any more.
- The injection can result in a delayed return to fertility but will not change a woman’s natural ability to become pregnant. On average it is four months (for the 3-month injection) or 1 month (for the 2-month injection) but could be as long as one year.
- Unlike condoms, it does not protect you from sexually transmitted infections such as HIV.
- Your regular bleeding pattern may change while using the injection. In the first three months you may have irregular or prolonged bleeding. Over time your monthly bleeding may stop or become infrequent or irregular. This is not harmful and will return to normal after you stop using the injection.
- Some women using the injection will gain or lose a small amount of weight. If weight gain occurs it will generally be in the range of 1-2kg per year but in rare cases may be up to 5kg.
- Some users may experience headaches, mood changes, dizziness or bloating.
- If you want to rely on the injections as a means of contraception then it is important that you attend for a follow up injection at around the right time. There is some flexibility in that you can be a couple of weeks early or late for your repeat injection and it will still be effective. But you should avoid being more than two weeks late or you may not be protected from pregnancy. If you are late for the injection, come as soon as you can and avoid sexual activity during this time or use condoms as a back up until you get your next injection.