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Cerelle contains 75 microgram of progesterone. For a progesterone to have emergency contraceptive effect , it will need to have 1.5 milligram of progesterone - which means 1500 microgram. So that means you will need to take 20 Cerelle, not 2.
An average birth control pill , ( not the cerelle, which is a minipill) contains about .5 mg of progesterone, so taking 3 tablets are enough.