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 contraceptive injection 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 contraceptive injection work best for me?

You can start using the contraceptive injection whenever you want. If you get your first shot within the first 7 days after the start of your period, If you get it at any other time in your cycle, you need to use another form of contraception (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