What acually causes brown discharge and blood when on depo? i've been on it for about a year now. i don't understand why i have brown discharge.

Depo: Its the lining of your uterus being so suppressed by the Progesterone effect of the Depo-Provera that it breaks down and your body cannot react to that by making estrogen to heal it due to the also suppressive effect of Depo-Provera on ovulation. Sometimes a short course of estrogen pills for a few weeks can help with that but over time this may come back, and you then take estrogen again.