Contraceptive Injection

Authored by , Reviewed by Dr Hannah Gronow | Last edited | Meets Patient’s editorial guidelines

The contraceptive injection contains a progestogen hormone. It has been used since the 1960s and is used worldwide. It is very effective.

The contraceptive injection contains a progestogen hormone called depo medroxyprogesterone acetate (DMPA). Progestogen hormones are very similar to a woman's own hormone called progesterone. Depo-Provera® is the brand used most often and it is given every 12 weeks. Sayana Press® is very similar to Depo-Provera® and also contains DMPA. Noristerat® is a brand which is rarely used. It is just used when very effective contraception is needed but only for a few months - for example, after a partner has had a vasectomy. The rest of this leaflet is about the injections that contain DMPA.

The contraceptive injection is sometimes called a LARC. This stands for long-acting reversible contraceptive. You can read about the other LARCs that contain progestogen in our separate leaflets called Contraceptive Implant and Intrauterine System. There is also a separate leaflet on the LARC which doesn't contain any hormone, called the Intrauterine Contraceptive Device (The Coil).

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

How effective is the contraceptive injection?

Dr Rosemary Leonard MBE

It is very effective. Between 2-60 women in every 1,000 using it will become pregnant after two years. Compare this to when no contraception is used: more than 800 in 1,000 sexually active women who do not use contraception become pregnant within one year.

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  • 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.
  • Periods often stop completely, which is perfectly safe.
  • It may help some of the problems of periods, such as premenstrual tension, heavypainful periods  and endometriosis.
  • It can be used by many of the women who cannot take the combined pill.
  • It is not harmful to women with sickle cell disease and may even reduce the pain of a sickle crisis.
  • It may be taken by women who are on medication that would interfere with other forms of hormonal contraception - for example, medications for epilepsy or HIV.
  • It may reduce the chances of getting cancer of the ovary or cancer of the womb (endometrial cancer)
  • If you want to stop using it you don't have to go back to your doctor or nurse to have it removed; you just have to wait for it to wear off.
  • The injection cannot be removed once given. Any side-effects may last for more than 2-3 months, until the progestogen goes from your body.
  • As the injection is long-acting, it may take some time after the last injection for you to become fertile again. This time varies from woman to woman. Some women may not ovulate for 6-8 months after the last injection. Rarely, it can take more than a year 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, which many see as a benefit. The longer it is used, the more likely it is that periods will stop. After they have had the injection for a year, periods stop for about 7 in 10 women.

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 or nurse. You may be able to have your next injection early or be given other treatment to stop the bleeding. Irregular bleeding can sometimes be due to another reason, such as an infection. This may need to be treated. 

Apart from changes to periods, side-effects are uncommon. If one or more should occur, they often settle down over a couple of months or so. One possible side-effect is weight gain. This seems to be a particular problem for young women (under 18 years) who are already overweight when they start the injection. Some women also report fluid retention, worsening acne, headaches and breast discomfort. However, there is little evidence to say that the injection causes these symptoms.

The most common reason for women to stop having the injections is because of irregular bleeding.

The injection can lead to some 'thinning' of the bones. This does not usually cause any problems and the bones go back to normal when the injections are stopped. Using injectable contraception for many years might lead to more bone thinning. It is therefore recommended that you have a review every two years with your doctor or nurse. They will discuss if this method is still the best one for you.

Very occasionally, the injection can cause some pain or swelling at the site where the injection was given, particularly with Sayana Press®. 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).

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 'thinning' of the bones (osteoporosis) 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.
  • A close family history of osteoporosis.

The injection is given into a muscle, usually in the buttock, or into the thigh or tummy (abdomen). It should not be given during pregnancy. It is therefore important to be sure you are not pregnant when you have your first injection. However, if you were already pregnant without knowing, there is no evidence that it does the baby or the pregnancy any harm.

  • 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 immediately.
  • Further injections are then given up to 13 weeks apart.
  • If you miss your appointment, you can have the injection at any time, as long as you are certain you are not pregnant. Your practice nurse or doctor will advise you to use extra contraception (such as a condom) for seven days after the injection.
  • If you are late for your injection but have had sex and can't be certain that you aren't pregnant, you may still be able to have your injection. You will then need to do a pregnancy test three weeks later. This is what is called an 'off-label use' and not all practices will allow it.

Sayana Press® has been designed so that you can give it to yourself. This may be useful if you have trouble getting to your surgery or clinic. Your doctor or nurse can teach you how to do this safely.

The doctor or nurse will tell you which type of injection you have and how long it is until the next injection. 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.

Note: don't forget, you will lose protection against pregnancy if you are late in having the next injection.

Further reading and references