The depo shot (Depo-Provera) is an injection you get once every 3 months. It’s a safe and convenient. It works really well if you always get it on time

In this section :

1. How does the birth control shot work?

The Depo-Provera shot contains the hormone progestin.  Progestin stops you from getting pregnant  by preventing ovulation (Ovulation is the release of an egg from one of a woman's ovaries. After the egg is released, it travels down the fallopian tube, where fertilization by a sperm cell may 
occur). 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.

2. How do I make the shot work best for me?

You can start using the family planning shot whenever you want. If you get your first shot within the first 7 days after the start of your period, you’re protected from pregnancy right away. If you get it at any other time in your cycle, you need to use another form of birth control (like a condom) for the first week after getting the shot.
 
For more information on the Depo Shot: http://www.fpasrilanka.org/content/depo-provera

Other Topics:

Condoms

The oral contraceptive pill

IUD

Implant

Emergency Contraceptive Pill