Contraceptive Injection

The contraceptive injection is a hormonal method of long-acting, reversible contraception.

  • It is 94% effective in preventing pregnancy.
  • You do not need to remember to take it every day.
  • You don’t have to prepare for, or interrupt, sex.

It is the 5th most popular method of contraception in the UK. People who have a uterus can use the contraception injection. There are 3 types available for free on the NHS.

They all contain the hormone progestogen.

What is progestogen?

The female-assigned reproductive system produces two hormones, oestrogen and progesterone. These hormones create your menstrual cycle. The hormones in contraception are artificial versions of natural hormones. Progestogen is the copy of progesterone. Slight variations in progestogen or how it is released in your body may make a difference as to how you feel on your contraceptive method.

There are different ways of delivering the same dose of the ingredient (medroxyprogestagen acetate) to your body.

Sayana Press: You do 1 injection every 13 weeks from the comfort of your own home.

Depo Provera: A Nurse or Doctor does 1 injection every 12 weeks at your local sexual health clinic or GP. In the UK, this is the most common type of injection.

Noristerat: There is an alternative form of injectable contraception. This contains the hormone norethisterone which is a different type of progestagen. A Nurse or Doctor does 1 injection every 8 weeks at your local sexual health clinic or GP.

SH:24 only offers Sayana Press. We can only prescribe Sayana Press to people who have used it before.

An important factor is that once the injection is given, it cannot be taken out so it will continue to have its effects for at least the following 13 weeks.

It can take up to one year for your fertility and periods to return to normal after the injection wears off, so it may not be suitable if you want to have a baby in the near future.

How does it work?

Diagram showing how the injection prevents ovulation, thickens cervical mucus and thins the womb lining

The contraceptive injection prevents pregnancy in three different ways:

  • It prevents ovulation. It stops the ovaries from releasing an egg each month. This means there is no egg for the sperm to fertilise. This is the main way it prevents pregnancy.
  • It thickens the mucus in the cervix (neck of the womb). The mucus partially blocks the entrance to the womb (uterus) so it is harder for sperm to enter and fertilise an egg.
  • It thins the lining of the womb. If an egg had been produced and fertilised, there is less chance of it implanting into the womb to create a pregnancy.

Your health & the injection

All methods of contraception have:

  • health benefits which are factors that could improve your health
  • side effects which are symptoms that do not affect your health but can affect the quality of your life in either a positive or negative way
  • health risks which are factors that could have an important negative impact on your health

Health benefits

The injection may provide some protection against cancer of the womb and pelvic inflammatory disease.

For people with sickle cell disease, the injection may help to lower the severity of sickle cell crisis pain.

Side effects

Periods and bleeding

The contraceptive injection changes the pattern of your bleeding. Your periods may stop or you might have irregular bleeding. This is when your bleeding does not happen at the same time each month.

We might recommend the contraceptive injection for people who have problems with their periods, because it can cause them to stop. For example,

  • premenstrual syndrome
  • heavy periods
  • painful periods
  • endometriosis

Although some people have no bleeding from the start, irregular bleeding is very common in the first 6 months and then gradually settles. This is not dangerous in any way.

  • After 3 months of taking the injectable contraceptive 10% of women have no bleeding.
  • After 12 months of taking the injectable contraceptive 50% of women have no bleeding.
  • One in a hundred people have ongoing problems with irregular bleeding on the injectable contraception, so not everyone stops their period.

Depending on how it affects you, the change in bleeding pattern may be an advantage or a disadvantage. If you have a lot of irregular bleeding, it can be very inconvenient. If you have very light irregular bleeding, it may not bother you.

If you are struggling with irregular bleeding, your GP may prescribe the combined pill on a temporary basis. The combined pill contains oestrogen, which may stimulate a period and help to regulate your cycle.

Bleed vs Period

We use period to describe the bleeding that happens during a menstrual cycle. In the first half of your cycle, when you produce oestrogen, the lining of your womb builds up. In the second half of your cycle, if you have not become pregnant, the lining is released and comes out of your body as a period. This process repeats itself approximately every 28 days.

We use bleeding or a bleed to describe the bleeding that happens when you are using a contraceptive method that changes your menstrual cycle. When you take a progestogen-only method the lining of your womb stays the same throughout the cycle. Progestogen doesn’t always maintain the lining in the same way which is why some people experience bleeding. We do not know why some people experience irregular bleeding more than others.

We use spotting to describe the amount of blood. Spotting is a smaller amount of blood that is less than a period or a bleed.

Weight gain

Some people experience weight gain when using the contraceptive injection. We think this is because it can increase appetite, so you may feel hungrier than usual.

Weight gain is more common if you are:

  • under the age of 18
  • have a body mass index of over 30kg/m2

If you gain more than 5% of your body weight in the first 6 months of using the contraceptive injection, then you are likely to continue to gain weight.

For example,

  • If you weigh 57kg or 9 stone, 5% of your body weight would be 3kg or 6 pounds. This is just under half a stone.
  • If you weigh 70kg or 11 stone, 5% of your body weight would be 4kg or 8 pounds. This is just over half a stone.

Unproven side effects of the injection

Hair loss
There is no conclusive evidence to associate injectable contraceptives with hair loss. However, at least one large study has reported this side effect in up to 10% of women.

Headaches are common in the general population so it is difficult to show a causative effect. Some studies have shown that up to 15% of women experience headaches on the injectable contraceptive.

Other symptoms
Acne, mood swings and a decreased interest in sex have all been reported in users of injectable contraceptives but there is no proven link.

Health risks

Mental health

We do not know, for certain, what the relationship is between the contraceptive injection and low mood or depression. The evidence on this is conflicting with some studies showing an increased level of depression among users of injectable contraceptives and other studies showing no increased risk.

Bone density and Osteoporosis risk

Oestrogen plays a role in maintaining bone strength. It is usually produced during the first half of the menstrual cycle. The contraceptive injection stops ovulation which also stops the menstrual cycle. This means less oestrogen is produced. Lower levels of circulating oestrogen in the body are linked to a small loss in bone mineral density.

Bone density usually returns to normal when you stop using the contraceptive injection.

This is more important for some age groups:

  • Women who are under the age of 18 may not have reached their adult bone mineral density yet.
  • Women who are over the age of 45 years need to have maximum bone strength as they will lose bone mineral density after the menopause.

We have reviewed the current research. From the scientific evidence, it is not clear if the loss of bone density results in an increased risk of fractures e.g. a broken bone.

Other things that might cause lower bone mineral density include:

  • smoking

Things that might cause a higher bone mineral density include:

  • weight bearing exercise e.g. running
  • a healthy diet

Every 2 years, we have a discussion with all our contraceptive injection users to assess their risk of osteoporosis. Your GP or Sexual Health Clinic should do the same.

Breast cancer

There may be a small link between the injectable contraception and breast cancer. Any increased risk is likely to be very small and would reduce when you stop the injectable contraception.

Unproven risks

There has been extensive research to understand if the contraceptive injection increases the risk of getting HIV. To date, there is no conclusive evidence that the injectable contraceptives increase risk of HIV.

When will the injection prevent pregnancy?

If you have the contraceptive injection during the first five days of your period, you will be immediately protected against pregnancy.

If you have the injection on any other day of your cycle, you will not be protected against pregnancy for 7 days.

You can use male condoms, female condoms or the diaphragm to protect against pregnancy. You can also have non-penetrative sex, where the penis does not go in the vagina, during this time.

If you are taking the combined pill, patch or ring and have used it for at least 7 days before switching to the injection you will be covered for contraception immediately if you do not take the 7 day break. If you take the 7 day break before starting the injection then you will need to use additional contraception for the first 7 days of the injection.

If you are using the hormonal coil (IUS) called Mirena, the progestogen-only pill called Norgeston or Noriday and you switch to the injection then you will need to use additional protection for 7 days.

If you are using the progestogen-only pill that contains desogestrel or the implant (when it has been in place for less than 3 years) and you switch to the injection then you will be protected immediately.

If you are using the copper coil (IUD):

  • You will be protected immediately if the injection is used within the first 5 days of your menstrual cycle.
  • You will need to use additional protection for 7 days, if injection is used at any other time.

The contraceptive injection does not protect you from STIs. Consider using a barrier method such as a condom or dental dam as well if you think you are at risk of an STI.


Most people can use the contraceptive injection. At your GP or Sexual Health Clinic appointment, the clinician will check for any reasons why it might not be safe for you to use it.

If you can’t take oestrogen (the hormone in methods like the combined pill) you may be able to use the contraceptive injection.

The injection is suitable for trans and non-binary people with a uterus as it does not interfere with hormone treatments. It can be used for purposes other than preventing pregnancy, such as stopping periods. Testosterone therapy will not prevent pregnancy when used on its own.

The injection is not suitable for people who are pregnant.

It may not be suitable for people who:

  • Want to become pregnant within the next year
  • Are under 18
  • Are over 45
  • Want regular periods
  • Have bleeding in-between periods or after sex - it is important to rule out common causes of irregular bleeding before starting a method that may make your bleeding more irregular
  • Are at risk of osteoporosis.
  • Have more than one risk factors for cardiovascular disease (e.g. a combination of factors such as diabetes, smoking, family history of heart disease, age over 35)

Before you start

Before starting the injectable contraception, we advise that you are up to date with your cervical screening tests.

To find out if you need a cervical screening, there is more information on the NHS website.


From your GP, local sexual health services or online.

At the moment, SH:24 only prescribes Sayana Press. We can only prescribe it to people who have used it before. However, we are working hard to make it available to first time users in the near future.

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The injectable contraceptive will not have a long term impact on your fertility.

However, it can take up to one year for your fertility and periods to return to normal after the injection wears off. It may not be suitable if you want to have a baby within the next year.

Irregular bleeding may continue for months after you stop the injections.

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If you have one of the following, your GP may not think you are suitable for the contraceptive injection. These include, but are not limited to:

  • undiagnosed irregular vaginal bleeding, and are under investigations to understand the cause
  • high risk of low bone mineral density
  • current or past history of cardiovascular disease, such as, a heart attack or angina
  • blockages in your blood vessels, such as, intermittent claudication or transient ischaemic attacks (TIAs)
  • multiple risk factors for cardiovascular disease
  • current or past history of breast cancer
  • severe liver disease

The contraceptive injection may complicate all of these things.

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Yes, these are two different ways of delivering the same dose of the same hormone (medroxy progestagen acetate) to your body.

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If you think your next injection is more than 14 weeks since your last injection, then you should have it as soon as possible. You will need to:

  • Use condoms until your next injection.
  • Use condoms for 7 consecutive days after you’ve taken the injection.

If you think you might be at risk of pregnancy:

  • Do a pregnancy test before your next injection.
  • Do a pregnancy test 3 weeks after your late injection.

If you have had unprotected sex when your injection is late and are worried, you may need to use emergency contraception.

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Depo-Provera is given by an experienced Doctor or Nurse, in the arm or buttock so you do not have to do it yourself. These injections do not hurt any more than a normal injection - people feel a sharp pin prick when the needle goes in and some tenderness at the injection site afterwards.

Sayana press may not be the best method of contraception for you if you are very worried about injections. Most people get used to the self injection process. You can learn more about the process of self injection here.

If you would like support with the injection process please contact us. Our experienced clinical team can talk you through the process and offer additional information and support if you would find this helpful.

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If you have the injection during the first five days of your period, you will be immediately protected against becoming pregnant. This is because the injection works by stopping ovulation and at this time in your cycle you have not started the process of ovulation.

If you have the injection on any other day of your cycle, you will not be protected against pregnancy for up to 7 days. Use condoms or another method of contraception during this time. This is because the injectable contraceptive will take 7 days to suppress ovulation.

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Once it is inserted you cannot remove the injection but its effects will wear off after 8-13 weeks, depending on the type used.

If you are concerned about side effects then it might be helpful to keep a diary of these so that you can monitor any change as the injectable contraceptive wears off.

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There are no long term effects of using the injectable contraceptive except its impact on bone mineral density and a possible increased risk of cardiovascular disease.

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Yes, the injectable contraception can be used safely while you are breastfeeding and will not affect your milk supply.

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The contraception injection is discrete and is not visible. You may experience some irritation around the injection site but this fades after a few days.

However, if you use Sayana Press you will need to keep a small sharps box at home to dispose of the needles safely. This box can be dropped off at your GP or local pharmacy for disposal.

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