They are currently used by more than 100 million women worldwide and by almost 12 million women in the United States.
COCPs should be taken at approximately the same time every day.
The effectiveness of the combined oral contraceptive pill appears to be similar whether the active pills are taken continuously for prolonged periods of time or if they are taken for 21 active days and 7 days as placebo.
By continuing to take a pill everyday, users remain in the daily habit even during the week without hormones.
Failure to take pills during the placebo week does not impact the effectiveness of the pill, provided that daily ingestion of active pills is resumed at the end of the week.
Instead, it is the lack of hormones for a week that causes a withdrawal bleed.
If the pill formulation is monophasic, meaning each hormonal pill contains a fixed dose of hormones, it is possible to skip withdrawal bleeding and still remain protected against conception by skipping the placebo pills altogether and starting directly with the next packet.Then after 28 days, or 91 days depending on which type a person is using, users start a new pack and a new cycle.If used exactly as instructed, the estimated risk of getting pregnant is 0.3%, or about 3 in 1000 women on COCPs will become pregnant within one year.Marketed as Anya or Lybrel, studies have shown that after seven months, 71% of users no longer had any breakthrough bleeding, the most common side effect of going longer periods of time without breaks from active pills.While more research needs to be done to assess the long term safety of using COCP's continuously, studies have shown no difference in short term adverse effects when comparing continuous use versus cyclic use of birth control pills.Attempting this with bi- or tri-phasic pill formulations carries an increased risk of breakthrough bleeding and may be undesirable.