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Unwanted 72 is a progesterone hormonal
pill and is used and designed as a emergency contraceptive
so when you have sex and if you take it in 12 and 24 hours with in 4-8 days you get periods.So if you use it once a month there can be problems like disturbances in periods;untimely bleeding etc.So if you want you can take once but if you have regular sex or more than once then it will be better to use the daily pill so that you get protection from unwanted pregnancy
as well as it will help you maintain your periods regular.