Depo Provera - a shot of progesterone administered by a doctor every 3 months. The shot is 99% effective in preventing pregnancy but does not prevent STD's. As the shot contains no estrogen, there are no estrogen related side effects such are experienced with the pill but similar side effects may still be experienced.
Most women who get the shot will experience some irregular bleeding, such as spotting or excessive bleeding. Advantages of the shot are that women who smoke, who are breastfeeding, or are over 35 years of age can use it safely.