Contraceptive Injection

What is the contraceptive injection?

The contraceptive injection contains a progestogen hormone. It has been used since the 1960s and is widely used world-wide. Depo-provera® is the brand used most often and it is given every 12 weeks. Noristerat® is another brand and it is given every 8 weeks.

How does the contraceptive injection work?

The progestogen is injected into a muscle and then is gradually released into the bloodstream. It works mainly by stopping ovulation (the release of the egg from the ovary). It also thickens the mucus made by the cervix which forms a 'mucus plug' in the cervix. This stops sperm getting through to the uterus (womb) to fertilise an egg. It also makes the lining of the uterus thinner. This makes it unlikely that a fertilised egg will be able to attach to the uterus.

How effective is the contraceptive injection?

It is more than 99% effective. This means that less than one woman in 100 who use this method of contraception will become pregnant each year. (Compare this to when no contraception is used. More than 80 in 100 sexually active women who do not use contraception become pregnant within one year.)

What are the advantages of the contraceptive injection?

• You do not have to remember to take a pill every day.
• You only have to think about contraception every 2-3 months.
• It does not interfere with sex.
• It can be used when breastfeeding.
• It may help some of the problems of periods, such as pre-menstrual tension, heavy periods and pain.
• It can used by some women who cannot take the combined pill (which contains oestrogen).
• It may help protect against pelvic infection. (The mucus plug in the cervix may help stop bacteria travel into the uterus.)

What are the disadvantages of the contraceptive injection?

• The injection cannot be removed once given, so any side effects last for more than 2-3 months until the progesterone goes from your body.
• As the injection is long acting, it takes some time after the last injection for its effect on fertility to wear off. This time varies from woman to woman. Some women take 6-8 months after the last injection before fertility returns. Rarely, it can take up to two years before fertility returns. This delay is not related to the length of time you use this method of contraception.
• Your periods are likely to change. During the first few months some women have irregular bleeding which can be heavier and longer than normal. However, it is unusual for heavy periods to persist. After the first few months it is more common for the periods to become lighter than usual, although they may be irregular. Many women have no periods at all. The longer it is used, the more likely periods will stop. Periods stop for about 7 in 10 women after they have had the injection for a year.

Some women find that having unpredictable or irregular periods can be a nuisance. However, if you do develop irregular bleeding while receiving the injection then you should inform your doctor. Irregular bleeding can sometimes be due to another reason, for example an infection, which may need to be treated.

Are there any side effects with the contraceptive injection?

Apart from changes to periods, side-effects are uncommon. If one or more do occur, they often settle down over a couple of months or so. Examples of possible side-effects include weight gain, fluid retention, increase in acne and breast discomfort. The commonest reason for women to stop having the injections is because of altered bleeding.

Having the injections can lead to some thinning of the bones in some women. This does not cause any problems and the bones usually revert back to normal when the injections are stopped. This is usually more significant if you were to have the injectable contraception for many years. It is therefore recommended that you have a review of the need to continue with your injectable contraception every two years with your doctor or nurse.

Very occasionally, the injection can cause some pain or swelling at the site where the injection was given. You should see your doctor or nurse if you have any signs or symptoms of infection at the site of injection (for example redness or swelling).

Who cannot have the contraceptive injection?

Most women can have the contraceptive injection. Your doctor or family planning nurse will discuss any current and past illnesses. For example, you should not have it if you have recently had breast cancer or have hepatitis.

If you have risk factors for osteoporosis (thinning of the bone) then it is normally advisable to use another method of contraception. Examples of risk factors include not having a period for six months or more (as a result of over-exercising, extreme dieting or eating disorders), heavy drinking or a close family history of osteoporosis.

How is the contraceptive injection given?

The injection is given into a muscle, usually in the buttock. It should not be given during pregnancy. It is therefore important to be sure you are not pregnant when you have your first injection.

For this reason the first injection is usually given during the first 1-5 days of a period. If you have the injection within five days of starting a period, you will be protected against pregnancy from then on. Further injections are then given up to 12 weeks apart depending on the type used.

The doctor or nurse will tell you which type of injection you have and how long it is till the next injection. (It will either be 8 or 12 weeks, depending on the type used.) However, it can be given up to two weeks early. This may be convenient if, for example, you are due to be on a holiday when your next injection is due.

You will lose protection against pregnancy if you are late in having the next injection.

Further information

Your GP, practice nurse and pharmacist are good sources of information if you have any queries.

The fpa (formerly the family planning association) also provide information and advice.
fpa's Helpline: 0845 310 1334 or visit their website www.fpa.org.uk