3-monthly contraceptive injection
The 3-monthly contraceptive injection contains a synthetic progestogen hormone called medroxyprogesterone acetate1. It is injected every 12 weeks by a trained healthcare professional1. The contraceptive is injected into a muscle and the active ingredient is slowly released into the bloodstream1.
How the contraceptive injection works
The hormone within the 3-monthly contraceptive injection prevents the eggs in your ovaries from ripening. If an egg is not released from the ovaries during your menstrual cycle, it cannot become fertilised by sperm and result in pregnancy1. The hormone also causes changes in the lining of your womb that makes it less likely for pregnancy to occur and thickens the mucus (fluid secreted by the cervical glands) at the entrance of the womb, making it more difficult for sperm to enter1.
The 3-monthly contraceptive injection works for 12 weeks, and it cannot be reversed once given, unlike the intrauterine system, intrauterine device and the contraceptive implant that can be removed at any time with an immediate return to fertility1,2.
Administration of the contraceptive injection
The 3-monthly contraceptive injection is given every 12 weeks as a single intramuscular injection into the buttock or upper arm1. The first injection should be given during the first 5 days after the beginning of a normal menstrual period to ensure that the injection is not given to a pregnant woman1.
Your 3-monthly contraceptive injection is a single intramuscular injection into the buttock or upper arm.
If used following childbirth, the first injection can be given up to 5 days after having given birth if you are not breast-feeding or not less than 6 weeks after childbirth if you are breast-feeding1. Provided that the injection is given at the times stated above, then you are protected from pregnancy straight away and there is no need to take extra precautions1. If more than 89 days has passed since the last injection, pregnancy should be excluded before having another injection, after which additional contraceptive measures such as a condom should be used for the following 14 days1.
Removal of the contraceptive injection
To stop using the 3-monthly contraceptive injection you simply stop having the injections. The contraceptive effects wear off 12 weeks from your final injection, and while you can get pregnant within the next month it may take up to a year before your fertility is restored2. However, in most women the effect will have worn off 5 to 6 months after the last injection. Over 80 % of women will conceive within a year of their last injection1.
Effectiveness of the contraceptive injection (in preventing pregnancy)
The 3-monthly contraceptive injection is highly effective in preventing pregnancy. Pregnancy rates with this type of contraceptive are very low. Within the first year of use the pregnancy rate is between 2 (perfect use) and 60 (typical use) per thousand women3.
By using the 3-monthly contraceptive injection, no pregnancies can occur due to problems remembering to use the contraceptive.
Women who rely on their partner using condoms can typically experience a pregnancy rate of as high as 180 per thousand women per year (only 20 per thousand if used perfectly)3.
As with other long-acting reversible contraceptives (LARC), the injection system offers the advantage of a contraceptive that you don’t have to think about and which doesn’t stop the spontaneity of sex.
Tell your doctor if you are taking aminoglutethimide as this may affect the way your 3-monthly contraceptive injection works. Also tell your doctor if you are taking any other medicines. This includes ’over the counter’ medicines from the pharmacy1.
Return to fertility after using the contraceptive injection
Using the contraceptive injection while breastfeeding
Side-effects & the contraceptive injection
Changes to your periods
The 3-monthly contraceptive injection will probably have an effect on your periods and it is likely that you will have irregular and possibly lengthy bleeding or spotting (a small amount of blood loss)1. One third of women will not have any bleeding at all after the first injection1. After 4 injections, most women find that their periods have stopped completely but this is also nothing to worry about1.
If you experience very heavy or prolonged bleeding you should talk to your doctor. This happens rarely but can be treated easily1. The risk of heavy and prolonged bleeding is higher if the 3-monthly contraceptive injection is started after abortion or delivery.
When you stop using the 3-monthly contraceptive injection, your periods will return to normal in a few months1.
Very common and common side-effects
|Very common side-effects in more than 1/10 women||Common side-effects in more than 1/100 women|
For a comprehensive list of possible side-effects, including uncommon and rare, as well as information on specific areas of concern, go to the side-effects: 3-monthly contraceptive injection page.
When should you not use the contraceptive injection?
There are a number of medical conditions which may make it unsuitable for you to have the 3-monthly contraceptive injection. They include1:
- if you have had, or think you might have, cancer of the breast or sex organs
- if you have unusual vaginal bleeding the cause of which is unknown
- if you are allergic to medroxyprogesterone acetate or any of the other ingredients of the 3-monthly contraceptive injection
- if you think you may be pregnant
- if you have not started getting your periods
- if you have or have had jaundice (yellowing of the skin) or severe liver disease (when the liver is not functioning properly), and liver function test results (blood tests that check liver function) have not returned to normal
- if you are using certain medicines such as high dose glucocorticoids (steroids), anti-epileptics, and thyroid hormones. (Tell your healthcare professional if you are taking these or any other medicines - they may recommend a more suitable method of contraception)
- because prolonged use of this method may cause bones to become thinner, if you wish to use the 3-monthly contraceptive injection for more than 2 years, you should talk to your doctor whether it is still the best option for you. Teenagers should use the 3-monthly contraceptive injection only if other methods of contraception are not acceptable.
Use with caution
Before your healthcare professional prescribes the 3-monthly contraceptive injection, you will have a physical examination. It is important to tell your healthcare professional if you have had or currently have any of the following conditions1. (Your healthcare professional can then discuss with you whether the 3-monthly contraceptive injection is suitable).
- migraine headaches
- diabetes or a family history of diabetes
- severe pain or swelling in the calf (indicating a possible clot in the leg, which may be called phlebitis)
- past pulmonary embolism or stroke while using the 3-monthly contraceptive injection
- problems with your eyesight while using the 3-monthly contraceptive injection
- history of depression
- problems with your liver or liver disease
- history of heart disease or cholesterol problems including any family history
- if you have recently had a ’hydatidiform mole’ which is a type of abnormal pregnancy