The two available versions of the contraceptive injection are the Depo-Provera and the Noristerat. The Depo-Provera is the most popular injection and lasts for 12 weeks, the Noristerat lasting for eight.
All contraception works by preventing a man’s sperm reaching the eggs, or ova, in the womb and fertilising one of them. Progestogen is injected into the woman to thicken the mucus in the cervix and this acts as a barrier to the sperm reaching the ova. The progestogen also prevents a fertilised egg implanting in the womb by thinning the lining. Some women may find they stop ovulating altogether when they are given the contraceptive injection.
This type of contraception is a convenient choice for women who don’t want to rely on taking the pill every day or for those who suffer reactions to the contraceptive pill.
There are some side effects of the injection, the most common of which are weight gain, mood swings, headaches and tenderness in the breasts. On the plus side, there is evidence of protection against cancer of the womb and pelvic inflammatory disease in those given the contraceptive injection.
Any side effects will become evident during the period of time the injection lasts (either eight or 12 weeks depending on what type you have been given) and may last for a few weeks longer.
Irregular periods are a common feature. For some women, their periods may get longer or shorter while for some they may stop altogether. This is not unusual and nothing to be concerned about but if you are worried about changes to your menstrual cycle, talk things over with your GP or practice nurse.
The contraceptive injection may not be the ideal choice if you plan to try for a baby immediately its effects wear off – your fertility may not return to normal for up to a year.
Depo-Provera is known to alter oestrogen levels with the knock-on effect of thinning of the bones but the bone repairs itself once the injections are stopped. If you have a family history of osteoporosis or already have low oestrogen, Depo-Provera may not be a suitable choice for you. If you are under 19, your body is still growing and your doctor will only prescribe Depo-Provera after a thorough consultation.