The Depo-Provera injection contains progestin, a hormone that prevents pregnancy by keeping your ovaries from releasing eggs. It also thickens your cervical mucus, which helps block sperm from getting to the egg in the first place.
If you're the kind of person who would have trouble remembering to take a pill every day, the shot might be a good option. You only need to remember to do something once every three months.
No one can tell when you're on Depo. There's no packaging and nothing you need to do before you have sex.
If you're really that scared of needles, then Depo is not for you.
It is possible to get pregnant as soon as 12 weeks following the last injection, though for some users it can take around 9 months. Don't take any chances. If you're not ready for a baby, protect yourself with another method.