Oral contraception, after eight years of use, is now recognized as the most effective method of voluntarily preventing pregnancy, probably because of a threefold action of the progesterone-estrogen combinations which inhibit ovulation, make cervical mucus impenetrable to sperm, and render the endometrium unsuitable for implantation. Several medical questions regarding safety are still unanswered, particularly those relating to thromboembolic complications; however, in this long-term study in which was used norethindronemestranol combinations, no serious complications were noted and laboratory studies have shown no statistically significant differences between users and nonusers of oral contraceptives. Minor side effects infrequently led to discontinuance of the method. Two dosage forms, one containing 10 mg of norethindrone and one containing 2 mg were equally effective.
Tyler ET. Current Status of Oral Contraception. JAMA. 1964;187(8):562–565. doi:10.1001/jama.1964.03060210012002
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