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Pharmacology: Norethisterone has pharmacological properties similar to progesterone.
Norethisterone is absorbed from the gastrointestinal tract and its effect last for at least 24 hours. When injected, it is detectable in the plasma after 2 days and is not completely excreted in the urine after 5 days.
Norethisterone has progestational actions similar to those of progesterone. It acts on the endometrium by converting the proliferative phase induced by oestrogen to a secretory phase. It inhibits the secretion of pituitary gonadotropins, which in turn presents follicular maturation and ovulation. Norethisterone is a more potent inhibitor of ovulation to progesterone and in addition it has weak oestrogenic and androgenic properties.
