Anovulatory cycle
While the normal menstrual cycle in the human typically lasts 4 weeks (28 days, range 24–35 days) and consists of a follicular phase, ovulation, and a luteal phase, followed by either menstruation or pregnancy, the anovulatory cycle has cycle
lengths of varying degrees. In many circumstances, menstrual intervals are prolonged exceeding 35 days leading to oligomenorrhea (cycle >35 – 180 days interval), or even longer, amenorrhea. In other cases, menstruation may be fairly regular (eumenorrhea), or more frequent (intervals < 21 days), or there may be a loss of menstrual pattern (menorrhagia, dysfunctional uterine bleeding).
Extended cycle combined hormonal contraceptive
With all extended-cycle COCPs, breakthrough bleeding is the most common side effect, although it tends to decrease over time. In a 12-month study of a continuous COCP regimen, 59% of women experienced no bleeding in months six through twelve and 79% of women experienced no bleeding in month twelve. Extended or continuous use of COCPs or other combined hormonal contraceptives carries the same risk of side effects and medical risks as traditional COCP use. 
One of the early extended-cycle COCPs, Seasonale, was marketed with the campaign, ""Fewer periods. More possibilities."" In December 2004, Barr Pharmaceuticals was warned by the FDA concerning these television advertisements. As the warning stated, ""By omitting and minimizing the risks associated with Seasonale, the TV ad misleadingly suggests that Seasonale is safer than has been demonstrated by substantial evidence or substantial clinical experience."" Although clinical studies had proven Seasonale to be effective in preventing pregnancy, the FDA felt the commercial advertisements omitted the common side effects of irregular vaginal bleeding or spotting.