A Cochrane review [Abstract] 1 included 1 trial of limited quality comparing a biphasic and monophasic preparation (Percival-Smith 1990). The study examined 533 user cycles of a biphasic pill (500 µg norethindrone/35 µg ethinyl estradiol for 10 days, followed by 1000 µg norethindrone/35 µg ethinyl estradiol for 11 days; Ortho 10/11) and 481 user cycles of a monophasic contraceptive pill (1500 µg norethindrone acetate/30 µg ethinyl estradiol daily; Loestrin). The study found no significant differences in intermenstrual bleeding, amenorrhea and study discontinuation due to intermenstrual bleeding between the biphasic and monophasic oral contraceptive pills.
Comment: The quality of evidence is downgraded by study limitations (no information on method of randomization or allocation concealment, high discontinuation rate after randomization) and sparse data.
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