Biphasic birth control pills provide a lower ratio of estrogen/progestin during the first half of the pill cycle and a higher dose during the second half in order to mimic the pattern of increasing and decreasing estrogen and progesterone levels during a woman’s regular menstrual cycle.
How it Works
The biphasic birth control pill delivers the same amount of estrogen every day for the first 21 days of the cycle. But the progestin/estrogen ratio is lower during the first 14 days. This causes the lining of the uterus to thicken, preventing sperm from reaching the egg. Over the next seven days, the ratio of progestin/estrogen is much higher which results in the shedding of the uterus lining. Women are thus required to use the same dose for the first seven to 10 days followed by a higher dose from day 11 to day 14. Some biphasic birth control pills have placebo pills at the end of the pack, while some have low-estrogren pills. Here are the two different types of 28-day biphasic pill packs:
- 21 active pills + 2 placebo pills + 5 low-estrogen pills
- 24 active pills + 2 low-estrogen pills + 2 placebo pills
Why Biphasic Birth Control?
The primary difference between the three formulations is in the dose of estrogen and progestin. Monophasic birth control pills deliver the same amount of estrogen and progestin in each pill throughout the pill cycle, while with triphasic birth control pills the doses of hormones changes every seven days throughout the pill cycle. However, it is important to understand that all three formulations are equally effective. There is no evidence indicating that biphasic birth control pills are inferior or superior to the monophasic or triphasic pills. In general, the selection of a birth control pill is strictly based on personal preference and tolerance. Biphasic birth control pills are different because the dose increases over the cycle which reduces the incidence of spotting and breakthrough bleeding as compared to monophasic birth control pills. Some women tolerate biphasic birth control pills better while others are more comfortable with triphasic pills.