How effective any contraceptive is depends on how old you are, how often you have sex and whether you follow the instructions.
If 100 sexually active women don’t use any contraception, 80 to 90 will get pregnant in a year.
If the injection is always used perfectly, according to instructions, it’s over 99% effective. This means that fewer than one injection-user in 100 will get pregnant in one year.
If the injection is not always used according to instructions, about six in 100 injection-users will get pregnant in one year.
It’s important to have your next injection at the right time. If you miss, or are late, having the next injection you may no longer be protected against pregnancy.
The injection is a method of long-acting reversible contraception (LARC). LARC is very effective because while it’s being used you don’t have to remember to take or use contraception.