The Contraceptive Injection

What is the contraceptive injection?

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

The progestogen is injected into a muscle and 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 1 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.)

• 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.)

• The injection cannot be removed once given, so its effect lasts 2-3 months. If side-effects occur there is little that can be done about them.
• Because the injection is long acting, it takes some time after the last injection for its effect 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 2 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. But, 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 in about half of users within 12 months of use. Some women worry about changes to their periods, but they are of no consequence. However, unpredictable or irregular periods can be a nuisance.

Your doctor or family planning nurse will discuss any current and past illnesses. Some illnesses may mean you cannot use the contraceptive injection. However, the number of women this affects is small.

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: headaches, mood swings, weight gain, reduced sex drive, fluid retention, increase in acne, and breast discomfort.

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 1-3 days of a period. If you have the injection within 5 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.)

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

Do other medicines interfere with the contraceptive injection?

Some prescribed medicines may interfere with the progestogen (mainly some used for epilepsy and TB). Tell the doctor or pharmacist that you have a contraceptive injection if you are prescribed another medicine. It is unlikely that a medicine bought without the need of a prescription will interfere. If in doubt, ask the pharmacist.

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

Further reading

1. Contraception Anne Szarewski and John Guillebaud
   252 pages 3rd Ed 2000 Oxford University Press; ISBN: 0192632566
2. Contraception: Your Questions Answered John Guillebaud
   552 pages 3rd Ed 1999 Churchill Livingstone; ISBN: 044306153X

© EMIS and PIP 2004   Updated: July 2002   CHIQ Accredited