The contraceptive injection is an injection which is given intramuscular (IM – into the muscle)(Depo – Provera) or subcutaneously (SC – under the skin) (Sayana Press).

The injection contains a progestogen hormone which is similar to the naturally produced progesterone by the ovaries.

The main way it works is to stop your ovaries releasing an egg each month (ovulation).

It also:

  • thickens the mucus in your cervix (neck of the womb), making it difficult for sperm to move through it and reach an egg
  • makes the lining of your uterus (womb) thinner so it’s less likely for a fertilised egg to be able to implant into the womb and create a pregnancy.

It’s common for your bleeding pattern to change while you’re using the contraceptive injection.

Bleeding may be irregular, lighter, shorter, more frequent, less frequent, last longer or stop altogether. This may settle down and isn’t harmful. If you have any concerns, see your doctor or nurse.

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

If the injection is not always used according to instructions, about six in 100 injection users will get pregnant in one 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 is 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 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 illness 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
  • have breast cancer
  • have unexplained vaginal bleeding (for example, bleeding between periods or after sex)
  • have arterial disease or history of serious heart disease or stroke
  • have severe disease of the liver
  • have risk factors for osteoporosis (thinning of the bones)

If you’re healthy and there are no medical reasons for you not to use the progestogen only injection, you can use it until the age of 50 years old.

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 (see below, 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 re-assessed every two years.

The doctor or nurse may ask you about your lifestyle and discuss whether it’d be more suitable for you to use a different method of contraception.

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.

Your bleeding pattern may change in a way that’s not acceptable to you; this is particularly true when you first start the progestogen only injection (or any method of hormonal contraception). Lots of women may stop bleeding completely with the injection and this is nothing to worry about.

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

The injection works for 13 weeks. 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 one 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. 

You may get some temporary side effects when you first start using the progestogen only injection, such as skin changes, breast tenderness and headaches. These often settle within a few months.

Research about the risk of breast cancer and hormonal contraception is complex and contradictory. Research suggests women who use hormonal contraception may have a small increase in the risk of being diagnosed with breast cancer compared to women who don’t use hormonal contraception.

Using Depo-Provera or Sayana Press may affect your bones

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.

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.

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.

You can normally start taking the Progestogen only injection at any point in your menstrual cycle.

There is special guidance if you have just had a baby, abortion or miscarriage.

You can start the Progestogen only injection at any time in your menstrual cycle if you’re sure you’re not pregnant.

If you start the injection:

  • On the first day of your period, you’ll be protected from pregnancy immediately.
  • Up to, and including, the fifth day of your period, you’ll be protected from pregnancy immediately.
  • At any other time in your menstrual cycle, you’ll need to avoid sex or use additional contraception, such as condoms, for the first seven days.

If you have a short menstrual cycle with your period coming every 23 days or less, starting the injection as late as the fifth day of your period may not give you immediate contraceptive protection. This is because you may ovulate (release an egg) early in your menstrual cycle. You may wish to talk to your doctor or nurse about this and whether you need additional contraception for the first seven days.

If you start the progestogen only injection after having had unprotected sex or after taking emergency contraception please do a pregnancy test three weeks after the last time you had unprotected sex.

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

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

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.