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You can take Unwanted 72 or I-pill, both before or after sex. They can be effective upto 72 hours. Taking it both before and after intercourse will not increase its effectivity. So, no point taking it twice. One pill should be enough. However, more than once a month is not recommended.
In fact one should use these pills only in case of emergency like failure of regular pills or condom breakage. If you intend on having regular sex, it would be better to use regular oral contraceptive pills like Unwanted 21 or Loette once a day daily for 21 days. Start a new pack from second day of next period.