A Cochrane review «»1 «Edelman A, Micks E, Gallo MF et al. Continuous or ...»1 included 12 studies with a total of 3 628 subjects.
Study findings for combined oral contraceptives (COC) were similar between 28-day and extended cycles in regard to contraceptive efficacy
(i.e., pregnancy rates) and safety profiles. When compliance was reported, no difference
between 28-day and extended cycles was found. Participants reported high satisfaction
with both dosing regimens.
The few studies that reported menstrual symptoms found that the extended cycle group
fared better in terms of headaches, genital irritation, tiredness, bloating, and menstrual
pain. However, breast tenderness was increased in continuous dosing of the contraceptive
patch. 11/12 studies found that bleeding patterns were either equivalent between groups
or improved with extended or continuous cycles. Endometrial lining assessments by
ultrasound were done in a small number of participants and were all normal.The studies were too small to address efficacy, rare adverse events, and safety.