High dose birth control pill regimens (estrogen or progesterone) used shortly after intercourse. Effect: if fertilization has not taken place yet, within the moments from fertilization until the regime is taken, EC may act as a true contraceptive and block fertilization; more likely, there has been no fertilization, and therefore, no effect; or, if fertilization has occurred, the effect may cause an early abortion ["pre-implantation effect"]. Long-term effect on the female body of such high dose hormones is not known.
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