Hello ma am and welcome. I need more information with such an unspecific presentation like your age, sexual status, birth control history, contraceptive implants, other medications used, etc. The dark brown blood could be a side effect of something, but at this point I cannot really say what. If you have indulged in unprotected sexual intercourse then you could get a home pregnancy test conducted at the earliest, as this could possibly even be a miscarriage. Please meet your doctor for further evaluation. Best wishes.