Depo-Provera has a 99 % success rate in preventing pregnancy. If done properly, this method is highly effective. Another thing to keep in mind is that it takes almost 2 weeks for the drug to work effectively. During this period, other contraceptive methods should be used to ensure protection.
If the pregnancy is suspected, the medication. should not be injected. Similarly, if there is unexplained vaginal bleeding, then Depo-Provera should not be used.