A: Periods become fewer and lighter for most women on Depo Provera, and often stop altogether. The longer a woman uses the shot, the more likely her periods will stop, and it may take up to a year for periods to return after a woman’s last shot. But some women will have longer, heavier periods, and some may have increased light spotting and breakthrough bleeding–occasionally to the point of bleeding all the time.

Some good resources for more information around Depo Provera include the Wikipedia entry, Planned Parenthood, and from the manufacturer of Depo, Pfizer.