The available evidence is limited and the internal validity of these trials is questionable. Given the high losses to follow up, these reports may even be considered observational. Given that caveat, the biphasic pill containing norethindrone was associated with inferior cycle control compared with the triphasic pill containing levonorgestrel. The choice of progestin may be more important than the phasic regimen in determining bleeding patterns.
Clinical evaluation of two biphasic and one triphasic norgestrel/ethinyl estradiol regimens.
Four hundred and fifty-eight women were followed for 3,586 cycles in a controlled, randomized, open trial designed to compare two biphasic and one triphasic norgestrel/ethinyl estradiol (ee) regimens. The three regimens are effective and no pregnancies were reported. Cycle control was good with all three regimens but the incidence of intermenstrual bleeding was higher with the triphasic. With this regimen, total hormonal ingestion is well below the lowest fixed dose norgestrel/ethinyl estradiol preparation (300 mcg norgestrel and 30 mcg ee) in the original 10:1 ratio. It is concluded that the staggering of hormonal doses opens the possibility of contraception with less hormone intake than is possible when a fixed dose regimen is used.