The contraceptive injection releases the hormone progestogen into your bloodstream to prevent pregnancy. The 3 types are Depo-Provera, Sayana Press or Noristerat.
At a glance: the contraceptive injection
If used correctly, the contraceptive injection is 99% effective. This means than 1 woman in 100 who use the injection will become pregnant in a year.
In real world use about 6 women in 100 become pregnant in a year because people forget to get their next injection (94% effective).
The injection lasts for 8, 12 or 13 weeks (depending on the type). You don't have to think about contraception every day or every time you have sex.
It can be useful for women who might forget to take the contraceptive pill every day.
It can be useful for women who can't use contraception that contains oestrogen.
It's not affected by medication.
It may provide some protection against cancer of the womb and pelvic inflammatory disease.
Side effects can include weight gain, headaches, mood swings, breast tenderness, and irregular bleeding. The injection can't be removed from your body. So if you have side effects they'll last as long as the injection and for some time afterwards.
Your periods may become more irregular or longer, or stop altogether (amenorrhoea).
It can take up to 1 year for your fertility 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.
Using Depo-Provera affects your natural oestrogen levels, which can cause thinning of the bones.
The injection does not protect against sexually transmitted infections (STIs). Use condoms as well as the injection to protect yourself against STIs.
How the injection works
There are 3 types of contraceptive injections in the UK.
This lasts for 12 weeks and 5 days and is usually given by a health professional into a muscle in your bottom. It sometimes may be given in a muscle in your upper arm.
This lasts for 13 weeks. It's given under the skin (subcutaneously) in your abdomen or thigh and you'd normally learn to do this yourself.
This lasts for 8 weeks and is less frequently used. It's usually given by a health professional into a muscle in your bottom. It's usually used for short periods of time – for example, if your partner is waiting for a vasectomy.
The contraceptive injection steadily releases a progestogen hormone into your bloodstream. Progestogen is like the natural hormone progesterone, which is released by a woman's ovaries.
The continuous release of progestogen:
- stops a woman releasing an egg every month (ovulation)
- thickens the mucus from the cervix (neck of the womb), making it difficult for sperm to pass through to the womb and reach an unfertilised egg
- makes the lining of the womb thinner, so that it is unable to support a fertilised egg
The injection can be given at any time during your menstrual cycle, as long as you and your doctor are reasonably sure you are not pregnant.
When it starts to work
If you have the injection during the first 5 days of your cycle, you'll 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 up to 7 days. Use condoms or another method of contraception during this time.
After giving birth
You can have the contraceptive injection at any time after you have given birth, if you are not breastfeeding. If you are breastfeeding, the injection will usually be given after 6 weeks. It may be given earlier if necessary.
If you start injections on or before day 21 after giving birth, you'll be immediately protected against becoming pregnant.
If you start injections after day 21, you'll need to use extra contraception for the following 7 days.
It's safe to use contraceptive injections while you're breastfeeding.
After a miscarriage or abortion
You can have the injection immediately after a miscarriage or abortion. You'll be protected against pregnancy straight away.
If you have the injection more than 5 days after a miscarriage or abortion, you'll need to use extra contraception for 7 days.
Who can use the contraceptive injection?
Most women can be given the contraceptive injection.
It may not be suitable if you:
- think you might be pregnant
- want to keep having regular periods
- have bleeding in between periods or after sex
- have arterial disease or a history of heart disease or stroke
- have a recent blood clot in a blood vessel (thrombosis)
- have severe liver disease
- have breast cancer or have had it in the past
- have diabetes with complications
- have cirrhosis
- are at risk of osteoporosis
Advantages and disadvantages of the injection
The main advantages of the contraceptive injection are:
- each injection lasts for either 8, 12 or 13 weeks
- the injection does not interrupt sex
- the injection is an option if you cannot use oestrogen-based contraception, such as the combined pill, contraceptive patch or vaginal ring
- you do not have to remember to take a pill every day
- the injection is safe to use while you are breastfeeding
- the injection is not affected by other medicines
- the injection may reduce heavy, painful periods and help with premenstrual symptoms for some women
- the injection offers some protection from pelvic inflammatory disease (the mucus from the cervix may stop bacteria entering the womb) and may also give some protection against cancer of the womb
Using the contraceptive injection may have some disadvantages. You should consider these carefully before deciding if it's right for you.
Your periods may change significantly during the first year of using the injection. They'll usually become irregular and may be very heavy, or shorter and lighter, or stop altogether. This may settle down after the first year, but may continue as long as the injected progestogen remains in your body.
It can take a while for your periods and natural fertility to return after you stop using the injection. It takes around 8 to 12 weeks for injected progestogen to leave the body. You may have to wait longer for your periods to return to normal if you're trying to get pregnant.
Until you are ovulating regularly each month, it can be difficult to work out when you are at your most fertile. In some cases, it can take 3 months to a year for your periods to return to normal.
You may put on weight when you use the contraceptive injection, particularly if you're under 18 years old and are overweight with a BMI (body mass index) of 30 or over.
Other side effects that some women report are:
- tender breasts
- changes in mood
- loss of sex drive
Depo-Provera, oestrogen and bone risk
Using Depo-Provera affects your natural oestrogen levels, which can cause thinning of the bones. It does not increase your risk of breaking a bone. This isn't a problem for most women, because 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 a problem for women who already have an increased risk of developing osteoporosis. For example, because they have low oestrogen, or a family history of osteoporosis. It may also be a concern for women under 18 because the body is still making bone at this age. Women under 18 may use Depo-Provera, but only after careful evaluation by a doctor or nurse.
Will other medicines affect the injection?
No – the contraceptive injection is not affected by other medication.
Risks of the contraceptive injection
There's a small risk of infection at the site of the injection. In very rare cases, some people may have an allergic reaction to the injection.
Between 1 in 10 and 1 in 100 women using Sayana Press get a dimple at the site of the injection.
Where can you get the contraceptive injection?
Most types of contraception are available free in the UK. Contraception is free to all women and men through the NHS. You can get contraception at:
- most GP practices – talk to your GP or practice nurse
- sexual health clinics – they also offer contraceptive and STI testing services
- some young people’s services (phone 0800 22 44 88 for further information)
Contraception services are free and confidential, including for people under the age of 16.
If you're under 16 and want contraception, the doctor, nurse or pharmacists won't tell your parents (or carer). They'll provide you with contraception as long as they believe you fully understand the information you're given and are able to use the contraception safely.
Doctors and nurses have a responsibility to make sure that you are safe and free from harm. They'll encourage you to consider telling your parents (or carer), but they won't make you. The only time that a professional will not be able to keep confidentiality is if they believe you're at risk of serious harm, such as abuse. If this was the case they would usually discuss it with you first.
Source: Scottish Government
30 December 2022
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