How long does it take for depo-provera provera (medroxyprogesterone) to become effective. i have only been on it almost 2 months & have bleeding on & off. could i be pregnant?

Unlikely but . . .: If you receive your 1st depo-provera injection within 5-7d of start of your menses, then it takes effect immediately. It remains effective as long as you get your shots every 12wks. Spotting is a common side effect. 1-6 women in 100 can get pregnant if they don't get shots as directed. Check out http://www.Plannedparenthood.Org/health-topics/birth-control/birth-control-shot-depo-provera-4242.Htm.