The contraceptive injection is a very effective and safe form of contraception. Each injection lasts for either eight or twelve weeks, depending on the type of injection given.
What is the contraceptive injection?
The contraceptive injection contains a progestogen hormone. It has been used since the 1960s and is used worldwide. 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 the release of the egg from the ovary (ovulation). It also thickens the mucus made by the cervix which forms a mucus plug. This stops sperm getting through to the womb to fertilise an egg. It also makes the lining of the womb thinner. This makes it unlikely that a fertilised egg will be able to implant in the womb.
How effective is the contraceptive injection?
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 1000 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 breast-feeding.
- It may help some of the problems of periods, such as premenstrual tension, heavy periods and pain.
- It can be used by some women who cannot take the combined pill.
- It may help to protect against pelvic infection. The mucus plug in the cervix may stop bacteria travelling into the womb.
What are the disadvantages of the contraceptive injection?
- The injection cannot be removed once given. Any side-effects will 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 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 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, such as an infection. This 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 should 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 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 revert back to normal when the injections are stopped. Using injectable contraception for many years would 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. 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 immediately. Further injections are then given up to 12 weeks apart, depending on the type used. If you are unable to make an appointment within that 5 day window, you can have the injection anytime, as long as you are reasonably sure you are not pregnant. Your practice nurse or doctor will advise you to use extra contraception (such as a condom) for 7 days after the injection. This what is called an 'off label use' and not all practices will allow it.
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: you will lose protection against pregnancy if you are late in having the next injection.
Your GP, practice nurse and pharmacist are good sources of information if you have any queries.
The fpa (formerly the Family Planning Association) also provides information and advice.
fpa's Helpline: 0845 310 1334 or visit their website www.fpa.org.uk
Dr Tim Kenny
Dr Hayley Willacy
Dr Tim Kenny