The speed of effectiveness for Depo depends upon when in your menstrual cycle you got your shot. If you got your shot within the first 5 days of your period, then it should be effective immediately. If you started the Depo right after finishing a pack of oral contraceptives, it should also be effective right away. If you didn't get your shot at these times, you should use a "back-up" method such as a condom for at least the first 7 days. Of course, because no birth control method is perfect, using condoms in addition to Depo is a good idea, to eliminate the small possibility of pregnancy, and just as important, to protect from infection.

The weight gain is cumulative (according to our source): the average is 5.4 #'s the first year, 8.1#'s after 2 years, and 13.8#'s after 4 years of use. The weight gain is thought to be because of increased appetite, so watch what you eat.