How does the contraceptive injection work?
The most common injection used in the UK is intramuscular medroxyprogesterone acetate (otherwise known as Depo-Provera). The contraceptive injection works just like a mini pill
. It contains a progesterone (a type of sex hormone) which:
- thickens the mucus at the entrance to the womb (so sperm can’t get in)
- prevents ovulation (the release of an egg)
- makes it more difficult for a fertilised egg to implant by changing the lining of the womb
That it works in three ways means that even if one of these mechanisms should fail, you are still protected from pregnancy. In fact, the contraceptive injection is over 99% effective if injections are on time, which means that less than one in 100 women who use it get pregnant within a year. Sometimes it can be difficult to remember to have the injection on time so the overall effectiveness of the injection at preventing pregnancy is actually around 94%. The contraceptive pill is just as effective if used correctly but its effectiveness is diminished if you forget a tablet. With the Depo-Provera injection, all you have to remember is the regular visit to your GP, every 12 weeks.