The injection steadily releases the hormone progestogen into the bloodstream. As long as you are not pregnant, you can get the injection at any time. If used correctly, the injection is more than 99% effective at preventing pregnancy.
The injection steadily releases the hormone progestogen into the bloodstream. This stops an egg from being released every month, thickens the mucus from the entrance to the womb (so it is harder for sperm to pass through to the womb and reach an egg) and makes the lining of the womb thinner (so it isn’t as easy for the fertilised egg to implant onto the womb). As long as you are sure that you are not pregnant, you can get the injection at any time. If used correctly, the injection is more than 99% effective at preventing pregnancy.
The contraceptive injection can be used without problems in most cases. However, it may not be suitable if you:
- Think you might be pregnant.
- Want to keep having regular periods.
- Have been bleeding in between periods or after sex.
- Have arterial disease or a history of heart disease or stroke.
- Have a blood clot in a blood vessel (thrombosis).
- Have breast cancer or have had in the past.
- Have diabetes with complications.
- Have cirrhosis or liver tumours.
- Are at risk of osteoporosis.
- Each injection lasts for 12 or 13 weeks.
- The injection does not interrupt sex.
- The injection is an option if you cannot use oestrogen based contraception (for example, the combined pill, contraceptive patch or vaginal ring).
- The injection is safe to use while you are breastfeeding.
- The injection is not affected by other medicines.
- The injection may reduce heavy, painful periods and help with premenstrual symptoms in some cases.
- The injection offers some protection from cancer of the womb and ovary.
- Disrupted periods- in the first year of the injection your periods may become irregular, heavier, shorter or lighter but these may resolve with time.
- It can take a while for you to return to natural fertility after you stop using the injection.
- You may experience side effects such as weight gain, acne, tender breasts, changes in mood and loss of sex drive but these may resolve with time.
- Thinning of the bones may be a problem for those who already have increased risk of developing osteoporosis.
- There is a small risk of infection at the site of injection. In very rare cases, some people might have an allergic reaction to the injection.