Contraceptive injections contain a progestogen hormone which is similar to the natural progesterone that women produce in their ovaries.
There are two types of injection. Depo-Provera protects you from pregnancy for 12 weeks and Noristerat protects you for eight weeks. Depo-Provera is the most commonly used contraceptive injection in the UK.
Read this information to find out:
How effective any contraceptive is depends on how old you are, how often you have sex and whether you follow the instructions.
If 100 sexually active women don’t use any contraception, 80 to 90 will become pregnant in a year.
Contraceptive injections are over 99 per cent effective. This means less than four women in every 1,000 will get pregnant over two years.
The injection is a method of long-acting reversible contraception (LARC). All LARC is very effective because while it is being used you do not have to remember to take or use contraception.
The main way they work is to stop your ovaries releasing an egg each month (ovulation). They also:
Only a doctor or nurse can give you a contraceptive injection.
You can go to a contraception or sexual health clinic or to the doctor or nurse at a general practice. All treatment is free and confidential (see How to get help with your sexual health).
The hormone is injected into a muscle, usually in your buttocks. Depo-Provera can also sometimes be given in the arm. Noristerat is a thicker solution so you may find the injection is slightly more painful when it is given.
If you want to carry on using this method of contraception, you will need to have injections every 12 weeks if you have Depo-Provera injections, or every eight weeks if you have Noristerat.
You do not need to have a vaginal examination or a cervical screening test to have a contraceptive injection.
Most women can have a contraceptive injection.
Your doctor or nurse will need to ask you about your own and your family’s medical history to make sure a contraceptive injection is suitable. Do mention any illness or operations you have had.
Some of the conditions which may mean you should not use the injection are:
You have now or had in the past:
Your doctor or nurse should discuss all risks and benefits with you.
If you have risk factors for osteoporosis it is normally advisable to use another method of contraception. Your doctor or nurse will talk to you about this. These factors include:
You can help to make your bones healthier by doing regular weight-bearing exercise such as running and walking, eating a healthy diet adequate in calcium and vitamin D, and cutting down on drinking alcohol and smoking.
The National Osteoporosis Society website can give you more information.
It is not recommended that all women have a bone scan before they start a contraceptive injection. It may be useful for some women – usually those who have been identified as having risk factors for osteoporosis.
Your periods will probably change.
These changes may be a nuisance but they are not harmful.
If you do have prolonged bleeding it may be possible for the doctor or nurse to give you some additional hormone or medicine that can help control the bleeding. They may also check that the bleeding is not due to other causes, such as an infection.
Depo-Provera is associated with an increase in weight of up to 3kg (6.6lbs) over two years.
You can start a contraceptive injection any time in your menstrual cycle if it is certain that you are not pregnant. If you start the injection during the first five days of your period you will be protected against pregnancy immediately.
If you have it on any other day you will not be protected for the first seven days, so you will need to use additional contraception, such as condoms, during this time.
The injection can be started any time after you have given birth if you are not breastfeeding. If you start the injection before three weeks (21 days) you will be protected against pregnancy immediately. If it is started later than day 21 you will need to use an additional method of contraception for seven days.
If you are breastfeeding, the injection is usually given from six weeks after you have given birth. The injection can be started earlier if there are no other alternatives that you find acceptable. The injection can be used safely while you are breastfeeding and will not affect your milk supply.
Heavy and irregular bleeding is more likely to occur if you have the injection in the first few weeks after giving birth.
The injection can be started immediately after an abortion or miscarriage. You will be protected against pregnancy immediately.
While the injection is working nothing will make it less effective. Injectable contraception is not affected by:
It is important to go back at the right time for your next injection – every 12 weeks for Depo-Provera or every eight weeks for Noristerat.
If you miss, or are late having, the next injection it may mean that you are no longer protected against pregnancy. To ensure that you remain protected against pregnancy you should not be more than two weeks late for your next injection.
It is most likely that you will be offered the injection Depo-Provera as Noristerat is usually only used for short periods of time, for example, while waiting for a sterilisation operation to become effective. Your doctor or nurse can discuss with you which contraceptive injection is most suitable.
Contraceptive injections are highly effective methods of contraception. If you have had your injections on time, it is very unlikely that you will become pregnant.
If you think that you might be pregnant then do a pregnancy test or speak to your doctor or nurse as soon as possible. Using the contraceptive injection does not affect a pregnancy test.
If you do get pregnant while you are using the injection, there is no evidence that it will harm the baby.
You can continue to use Depo-Provera until you are 50 years old, provided there are no medical reasons not to use it and you are not at risk of osteoporosis (see How does Depo-Provera affect my bones? above).
If you do use the injection long-term you should expect to have your risk factors for osteoporosis re-assessed every two years. The doctor or nurse may ask you about your lifestyle and discuss whether it would be more suitable for you to use a different method of contraception.
If you want to stop a contraceptive injection all you need to do is not have your next injection.
Your periods and fertility may take a while to return to normal after you stop using a contraceptive injection. However, it is possible to get pregnant before your first period. If you don’t wish to become pregnant then you should use another method of contraception from the day that your injection would have been due. If you have sex without using another method of contraception you may want to consider using emergency contraception.
If you want to try for a baby start pre-pregnancy care such as taking folic acid and stopping smoking. You can ask your doctor or nurse for further advice.
No. It is not necessary to stop a contraceptive injection if you are having an operation. However, it is always recommended that you tell the doctor that you are using the contraceptive injection.
You only need to go to the clinic or your general practice when your injection is due. If you have any problems or want to ask any questions between injections, you should contact your doctor or nurse.
Last updated November 2012. Next update available October 2013.