Well it really does work differently in everyones system... however I was on the depo shot for 2 1/2 years- I went off the shot and didn't get my period back for 8 months. so you may be looking at a substantial time amount of time.
DEPO-PROVERA is an injection that uses a synthetic version of the hormone, progesterone (like the birth control pill), to prevent pregnancy. However, DEPO-PROVERA does not contain estrogen. You receive the injection from your health care provider. It is given in the buttocks or upper arm.
Like other hormonal birth control methods including the pill, DEPO-PROVERA causes a resting state in your ovaries. Since your ovaries do not release an egg each month, you cannot get pregnant.
I was on Depo-Provera for three years. After stopping the injections it took 1 year for my (normal)period to return, but I did have brownish spotting throughout the treatment-especially after intercourse."They" say it can take up to 18 months for your period to return to "normal". It really varies on your body, but it is common to not have a period while on the shot.