A woman can get pregnant if a man's sperm reaches one of her eggs (ova). Contraception tries to stop this happening by keeping the egg and sperm apart or by stopping egg production. One method of contraception is the injection.
There are three types of contraceptive injections in the UK: Depo-Provera, which lasts for 12 weeks, Sayana Press, which lasts for 13 weeks, and Noristerat, which lasts for eight weeks. The most popular is Depo-Provera. Noristerat is usually used for only short periods of time - for example, if your partner is waiting for a vasectomy.
The injection contains progestogen. This thickens the mucus in the cervix, stopping sperm reaching an egg. It also thins the womb lining and, in some, prevents the release of an egg.
At a glance: the contraceptive injection
- If used correctly, the contraceptive injection is more than 99% effective. This means that less than one woman in 100 who use the injection will become pregnant in a year.
- The injection lasts for eight, 12 or 13 weeks (depending on the type), so 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.
- The contraceptive injection 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). Treatment is available if your bleeding is heavy or longer than normal - talk to your doctor or nurse about this.
- It can take up to one 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). By using condoms as well as the injection, you'll help to protect yourself against STIs.
How the injection works
You can get contraception at:
- most GP surgeries
- community contraception clinics
- some GUM clinics
- sexual health clinics
- some young people's services
The contraceptive injections Depo-Provera and Noristerat are usually given into a muscle in your bottom, although sometimes may be given in a muscle in your upper arm. Sayana Press is given under the skin (subcutaneously) rather than into a muscle, in the abdomen or thigh.
The contraceptive injection works in the same way as the implant. It steadily releases the hormone progestogen into your bloodstream. Progestogen is similar to the natural hormone progesterone, which is released by a woman's ovaries during her period.
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 five days of your cycle, you will be immediately protected against becoming pregnant.
If you have the injection on any other day of your cycle, you will not be protected against pregnancy for up to seven 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 six weeks, although it may be given earlier if necessary.
- If you start injections on or before day 21 after giving birth, you will be immediately protected against becoming pregnant.
- If you start injections after day 21, you will need to use additional contraception for the following seven days.
Heavy and irregular bleeding is more likely to occur if you have the contraceptive injection during the first few weeks after giving birth.
It is safe to use contraceptive injections while you are breastfeeding.
After a miscarriage or abortion
You can have the injection immediately after a miscarriage or abortion, and you will be protected against pregnancy straight away. If you have the injection more than five days after a miscarriage or abortion, you'll need to use additional contraception for seven days.
Who can use the 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 blood clot in a blood vessel (thrombosis)
- have liver disease
- have migraines
- have breast cancer or have had it in the past
- have diabetes with complications
- have cirrhosis or liver tumours
- are at risk of osteoporosis
Advantages and disadvantages of the injection
The main advantages of the contraceptive injection are:
- each injection lasts for either eight, 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, which you should consider carefully before deciding on the right method of contraception for you. These are as follows:
Your periods may change significantly during the first year of using the injection. They will 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 eight to 12 weeks for injected progestogen to leave the body, but you may have to wait longer for your periods to return to normal if you are 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 three months to a year for your periods to return to normal.
You may put on weight when you use the contraceptive injection, particulaly if you are 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, but 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.
Will other medicines affect the injection?
No - the contraceptive injection is not affected by other medication.
There is 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.
Where you can get it
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 surgeries - talk to your GP or practice nurse
- community contraception clinics
- some genitourinary medicine (GUM) clinics
- sexual health clinics - they also offer contraceptive and STI testing services
- some young people's services (call 0300 123 7123 for more information)
Find your nearest sexual health clinic by searching your postcode or town.
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 pharmacist won't tell your parents (or carer) as long as they believe you fully understand the information you're given, and your decisions. Doctors and nurses work under strict guidelines when dealing with people under 16.
They'll encourage you to consider telling your parents, but they won't make you. The only time that a professional might want to tell someone else is if they believe you're at risk of harm, such as abuse. The risk would need to be serious, and they would usually discuss this with you first.
Article provided by NHS Choices