Side effects of birth control pills may keep women from using them as planned. Attempts to decrease side effects led to the three-phase pill in the 1980s. Pills with three phases provide different amounts of hormones over three weeks. One-phase pills have the same amount of hormone for three weeks. Whether three-phase pills lead to more pregnancies is unknown. Nor is it known if the pills give better cycle control or fewer side effects. This review looked at whether three-phase pills worked as well as one-phase pills. It also studied whether women had fewer side effects with these pills.
We did a computer search for studies of pills with three phases versus pills with one phase in May 2011. We also wrote to researchers and manufacturers to find other trials. We included randomized trials in any language. The studies had to follow women for at least three treatment cycles.
We found 23 trials that looked at three-phase versus one-phase birth control pills. Many studies did not have good methods and the authors did not always report all their methods. The two types of pills did not differ in the numbers of women who got pregnant. About half of the trials found better bleeding patterns with the three-phase pill. The numbers of women who stopped using the pills were about the same for both types of pills.
The evidence was not strong enough to say whether the three-phase pill was better than the one-phase pill for pregnancy prevention, bleeding patterns, or continued use. Therefore, we recommend one-phase pills for women starting to use birth control pills. Large trials that are of good quality are needed to see if pills with three phases work better than those with one phase.