If 100 sexually active women don’t use any contraception, 80 to 90 will get pregnant in a year.

If the injection is always used perfectly, according to instructions, it’s over 99% effective. This means that fewer than 1 in 100 injection-users will get pregnant in a year.

If the injection is not always used according to instructions, about 6 in 100 injection-users will get pregnant in a year.

It’s important to have your next injection at the right time. If you miss, or are late, having the next injection you may not be protected from pregnancy.

The injection’s a method of long-acting reversible contraception (LARC). LARC is very effective because while it’s being used you don’t 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:

• thicken the mucus from your cervix (entrance to the womb), making it difficult for sperm to move through it and reach an egg
• make the lining of your uterus (womb) thinner to stop a fertilised egg implanting.

You can get the injection from a contraception or sexual health clinic or a doctor or nurse at a GP surgery.

All treatment is free and confidential (see below for Where can I get more information and advice?

You’ll usually be offered Depo-Provera or Sayana Press. Your doctor or nurse can discuss with you which contraceptive injection is the most suitable for you.

For Depo-Provera or Sayana Press, you’ll need to have an injection once every 13 weeks.

Depo-Provera is injected into a muscle, usually in the buttocks. It can also sometimes be given in the arm.

Sayana Press is injected just beneath the skin at the front of the thigh or abdomen, with a tiny needle.

It’s possible for you to be taught how to inject Sayana Press yourself at home but not all clinics and GP surgeries currently offer this option. You should have a responsible adult with you when you inject Sayana Press in case you have a reaction to it (this is very unlikely).

Noristerat (which is given once every 8 weeks, injected into a muscle) isn’t commonly used in the UK.

You don’t need to have a vaginal examination or a cervical screening (smear) test to be given a contraceptive injection.

The contraceptive injection can be used by most people. 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 illnesses or operations you’ve had.

You may be advised not to use the injection if you:

• think you might already be pregnant
• don’t want your periods to change
• want a baby within the next year

You may be advised not to use the injection if you have or had in the past:

• breast cancer
• unexplained vaginal bleeding (for example, bleeding between periods or after sex)
• arterial disease or history of serious heart disease or stroke
• severe liver disease
• risk factors for osteoporosis (thinning of the bones). See Can I use a contraceptive injection if I’m at risk of osteoporosis?

Advantages:

• You don’t have to think about contraception for as long as the injection lasts
• It’s not affected by other medicines
• It may reduce heavy painful periods and help with premenstrual symptoms for some people
• You can use it if you’re breastfeeding
• It’s a good method if you can’t use oestrogens, like those in the combined pill, contraceptive patch and contraceptive vaginal ring

Disadvantages:

• Your periods may change in a way that’s not acceptable to you – also see Will a contraceptive injection affect my periods?
• Irregular bleeding may continue for some months after you stop the injections
• Some people may put on weight when they use Depo-Provera or Sayana Press – also see Will my weight be affected by a contraceptive injection?
• The injection works for 13 or 8 weeks, depending on which type you have. It can’t be removed from your body, so if you have any side effects, you have to be prepared for them to continue during this time and for some time afterwards
• There can be a delay of up to 1 year before the return of your periods and fertility after stopping the injection
• Contraceptive injections don’t protect you from sexually transmitted infections, so you may want to use condoms as well
• Some people experience side effects such as spotty skin, hair loss, decreased libido (sex drive), mood swings and headaches

• Using Depo-Provera or Sayana Press may affect your bones – also see How does a contraceptive injection affect my bones?
• Research on the risk of breast cancer and hormonal contraception use is complicated and hasn’t given definitive answers. The available research suggests that users of any hormonal contraception (including the injection) may be slightly more likely to be diagnosed with breast cancer, but the risk is small
• You can have an allergic reaction to the injection, but this is rare
• As with any injection, there’s a small risk of a reaction at the spot the injection is given, which may cause irritation, swelling or a scar

Your doctor or nurse should discuss all risks and benefits with you.

• Using Depo-Provera or Sayana Press affects your natural oestrogen levels, and may cause thinning of the bones. This isn’t normally a problem for most injection-users as the bone replaces itself when you stop the injection and it doesn’t appear to cause any long-term problems
• Thinning of the bones may be more of a problem if you already have risk factors for osteoporosis – see below for Can I use a contraceptive injection if I’m at risk of osteoporosis?
• If you’re under 18 years old you may use Depo-Provera or Sayana Press, but only after careful evaluation by a doctor or nurse. This is because young people under 18 are still making bone

If you have risk factors for osteoporosis (thinning of the bones) it’s normally advisable to use another method of contraception. Your doctor or nurse will talk to you about this. Risk factors include:

• being underweight
• smoking
• heavy drinking
• long-term use of steroids
• a close family history of osteoporosis
• certain medical conditions affecting the thyroid and digestive system

You can help to make your bones healthier by doing regular weight-bearing exercise such as running and walking, eating a healthy diet with enough calcium and vitamin D, cutting down on drinking alcohol, and stopping smoking.

The Royal Osteoporosis Society’s website – theros.org.uk – can give you more information.

A bone scan before starting a contraceptive injection isn’t usually recommended. It may be useful for some people – usually those who’ve been identified as having risk factors for osteoporosis.

Your periods will probably change.

• Most often, periods will stop completely
• Some injection-users will have irregular bleeding or spotting (bleeding between your usual bleeds)
• Some injection-users will have bleeding that lasts longer and is heavier

These changes may be a nuisance but they’re 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 isn’t due to other causes, such as an infection.

Depo-Provera and Sayana Press are associated with an increase in weight in some people. If you’re under 18 years old and overweight before starting Depo-Provera or Sayana Press, you may be more likely to gain weight with use.

You can start a contraceptive injection any time in your menstrual cycle if it’s certain that you’re not pregnant.

If you start the injection during the first 5 days of your period you’ll be protected against pregnancy immediately.

If you start it on any other day, you won’t be protected for the first 7 days. You’ll need to use additional contraception, such as condoms, or avoid sex during this time.

The injection can be started any time after giving birth. If you start the injection before 3 weeks (21 days) you’ll be protected against pregnancy immediately.

If it’s started later than day 21, you’ll need to use an additional method of contraception, such as condoms, or avoid sex for the first 7 days.

When using the injection within 6 weeks of giving birth, you may be more likely to have heavy and irregular bleeding.

The injection can be used safely if you’re breastfeeding.

The injection can be started immediately after an abortion or miscarriage and you’ll be protected against pregnancy straight away.

If you start the injection more than 5 days after a miscarriage or abortion then follow the advice in. Also see – When can I start using a contraceptive injection?

While the injection is working, nothing will make it less effective. The contraceptive injection isn’t affected by:

• prescribed medicines, including antibiotics
• any medicines which you buy over the counter at a pharmacy
• diarrhoea
• vomiting

It’s important to have your next injection at the right time – every 13 weeks for Depo-Provera and Sayana Press or every 8 weeks for Noristerat.

If you miss or are late having your next injection it may mean that you’re no longer protected against pregnancy.

Contraceptive injections are highly effective. If you’ve had your injection on time, it’s very unlikely that you’ll get 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 doesn’t affect a pregnancy test.

If you do get pregnant while you’re using the injection, there’s no evidence that it will harm the baby.

You can continue to use the injection until you’re 50 years old, as long as there are no medical reasons not to and you’re not at risk of osteoporosis – also see How does a contraceptive injection affect my bones?

If you use the injection for a long time, you should expect to have your risk factors for osteoporosis reassessed every 2 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 the injection. However, it’s possible to get pregnant before your first period after stopping the injection. If you don’t wish to get pregnant then 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 (see below).

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’s not necessary to stop a contraceptive injection if you’re having an operation. However, it’s always recommended that you tell the doctor you’re using a contraceptive injection.

You only need to go to the clinic or your GP surgery when your injection is due. If you have any problems or want to ask any questions between injections, contact your doctor or nurse.

If you’ve been given a supply of Sayana Press to inject at home, you’ll need to see a doctor or nurse at least once a year.