The contraceptive injection is a very effective and safe form of contraception. Each injection lasts foreither eight or twelve weeks, depending on the type of injection given.
The contraceptive injection contains a progestogen hormone. It has been used since the 1960s and is usedworldwide. Depo-Provera® is the brand used most often and it is given every 12 weeks. Noristerat® is anotherbrand 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 bystopping the release of the egg from the ovary (ovulation). It also thickens the mucus made by the cervix whichforms a mucus plug. This stops sperm getting through to the womb to fertilise an egg. It also makes the lining ofthe 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. Comparethis to when no contraception is used. More than 800 in 1000 sexually active women who do not usecontraception 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 every2-3 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 travellinginto 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, untilthe progesterone goes from your body. As the injection is long-acting, it takes some time after the last injection to become fertile again. Thistime varies from woman to woman. Some women may not ovulate for 6-8 months after the lastinjection. Rarely, it can take up to two years before fertility returns. This delay is not related to thelength of time you use this method of contraception. Your periods are likely to change. During the first few months some women have irregular bleedingwhich can be heavier and longer than normal. However, it is unusual for heavy periods to persist. Afterthe first few months it is more common for the periods to become lighter than usual, although theymay be irregular. Many women have no periods at all. The longer it is used, the more likely periods willstop. 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 developirregular bleeding while receiving the injection then you should inform your doctor. Irregular bleeding cansometimes 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 downover a couple of months or so. Examples of possible side-effects include weight gain, fluid retention, increase inacne 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 bonesrevert back to normal when the injections are stopped. Using injectable contraception for many years would leadto more bone thinning. It is therefore recommended that you have a review every two years with your doctor ornurse. 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. Youshould see your doctor or nurse if you have any signs or symptoms of infection at the site of injection (forexample, 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 currentand 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 methodof 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 thereforeimportant 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 injectionwithin five days of starting a period, you will be protected immediately. Further injections are then given up to 12weeks apart, depending on the type used. If you are unable to make an appointment within that 5 day window, youcan have the injection anytime, as long as you are reasonably sure you are not pregnant. Your practice nurse ordoctor will advise you to use extra contraception (such as a condom) for 7 days after the injection. This what iscalled 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 begiven up to two weeks early. This may be convenient if, for example, you are due to be on a holiday when yournext 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
, NICE Clinical guideline (October 2005) Faculty of Sexual and Reproductive Healthcare (2009) Bone mineral density in women aged 25-35 years receiving depotmedroxyprogesterone acetate: recovery following discontinuation. Contraception. 2006 Aug;74(2):90-9. Epub 2006 May 19.
Trussell J - Contraceptive Efficacy, In Hatcher RA, Trussell J, Nelson AL, Cates W, Kowal D, Policar M. ContraceptiveTechology: Twentieth Revised Edition. New York NY: Ardent Media, 2011. ,Faculty of Sexual & Reproductive Healthcare (June2013)
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