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Unwanted 72 is a emergency contraceptive pill
and is a hormonal
pill so you are sure to get withdrawal bleeding with in 3-7 days of taking the pill.The reason for bleeding is the sudden surge and drop in hormonal levels after taking the pill.The bleeding will be like periods and will stop in 4-5 days and if it does not stop then you have to consult a Gynaecologist.As for avoiding pregnancy
if you have sex a few times a month then it is better for you to get started on a regular birth control pill as it will help you to avoid pregnancy as well as keep your periods regular.