A depot shot prevents pregnancy by inhibiting ovulation, changing the cervical mucus to help prevent sperm from reaching the egg and by preventing the fertilized egg from implanting in the uterus by causing changes in the uterine lining. The chances of failure of the depot leading to pregnancy are 3 in 1000 with typical use.
The depot shot is mostly given after confirming that you are not pregnant either clinically by confirming that you are on the period while taking the shot or by a urine pregnancy test. Although a brownish discharge does not mean a pregnancy and spotting between periods is also common for women using the depot shots, if you are in doubt you can just do a urine pregnancy test to allay your fears.
If you use the depot regularly, then there is a 60% chance that you will be amenorrheic i.e you will have no periods after 12 months of use.Do not worry about this. Just do a urine pregnancy test whenever you are in doubt.
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.