Inconsistent pill use. How consistently women take the pill can affect the incidence of side effects. Missing pills or taking pills late can increase the occurrence of nausea, vomiting, spotting, and breakthrough bleeding (37, 124, 163, 179).

In fact, using the pill inconsistently can create a self-defeating sequence of events. For example, a woman misses a pill, causing spotting or breakthrough bleeding. She may take two pills the next day to make up for the missed pill, but this brings on nausea and perhaps vomiting. Because of these problems, she skips more pills—mistakenly thinking the break will alleviate her side effects—and so experiences more side effects. This chain of events can soon lead her to stop pill use altogether.

Many women discontinue the pill because they were not informed when they started that it can cause side effects (180, 235). When side effects are unexpected, they can be frightening. Telling pill users ahead of time about the possible common side effects and how inconsistent use can aggravate side effects are among the most important messages about pill use that providers can convey (see Chapter 4.2).

Breakthrough bleeding and spotting. For many women pill use makes periods more regular and reduces blood loss. Breakthrough bleeding and spotting, however, occur in some users and affect pill use, particularly when women do not understand why they are bleeding. Some women mistakenly think that irregular bleeding indicates a serious health problem, such as cancer (88, 166), and so they may stop taking the pill.

Covert pill users—that is, women using the pill without their partners' knowledge—fear that breakthrough bleeding will reveal their contraceptive use to their partners and families. Changes in menstrual patterns, irregular bleeding, and amenorrhea are a primary concern and often the main reason for discontinuation among covert pill users (22). Islamic women, for example, cannot pray while menstruating. Not attending prayers for weeks at a time could alert husbands and members of the extended family to covert contraceptive use (22).

In cultures where women's activities are restricted during menstruation, breakthrough bleeding amounts to far more than dealing with an unpleasant or frightening side effect. Women's participation in food preparation, religious rituals, community events, school attendance—in general, their mobility—is severely constrained while they are menstruating (13, 134). For example, some women in India cannot touch their children during menstruation, while others are forced to sleep away from their families (77). Prolonged or frequent bleeding episodes that limit women's everyday activities can contribute considerably to discontinuation of OC use.