Depo-Provera

The shot is just what it sounds like—a shot that keeps you from getting pregnant. Once you get it, your birth control is covered for three full months—there’s nothing else you have to do.

The birth control shot (sometimes called Depo-Provera, the Depo shot, or DMPA) contains the hormone progestin. Progestin stops you from getting pregnant by preventing ovulation. When there’s no egg in the tube, pregnancy can’t happen. It also works by making cervical mucus thicker. When the mucus on the cervix is thicker, the sperm can’t get through. And when the sperm and the egg can’t get together, pregnancy can’t happen.

When used perfectly, the birth control shot effectiveness is more than 99%, meaning less than 1 out of every 100 people who use it will get pregnant each year. But when it comes to real life, the shot is about 94% effective, because sometimes people forget to get their shots on time. So, in reality, about 6 out of every 100 shot users will get pregnant each year.

The better you are about getting your shot on time, the better it will work. But there’s a very small chance that you could still get pregnant, even if you always get the shot on time.