Why Do You Miss Your Pill?

One study found somewhat unexpected reasons for women missing their birth control pill (emphasis mine):

The 3 most frequent reasons cited by participants for missing pills were "away from home" (12.9%), "forgot" (12.9%), and "no new pack" (10.5%) ( Table 2 ). "Health" and "side effects" were the least likely to be cited. Health problems, such as nausea and vomiting, accounted for only 2.4% of missed pill instances, whereas side effects were cited as the reason for a missed pill only five times (1.3%) out of the 372 total instances of missed pills.

To prevent pills from being unavailable, the study's authors have a few suggestions:

...encourage women to keep a spare pack in their purse, at their boyfriend's house, or at other relevant locations. To avoid running out of pills, women might be encouraged to plan in advance and mark a day on their calendar reminding them to make a trip to the pharmacy. If insurance plans allow, these women might also be encouraged to buy more than one pill pack at a time and to fill their prescription at a 24-hour pharmacy. Reminders, such as a watch alarm, involving a responsible partner, or changing the current pill-taking time to a more appropriate time, may help to deal with forgetfulness. Consideration of over-the-counter access to OCs or access to a limited number of pills through a pharmacist might also be warranted, because it would enable women who forget to bring pills while traveling or away from home to continue taking their pills.

I think spare packs, and OTC access, particularly for women already using the Pill, would be the most practical solutions to this problem.

More from the study:

Oral contraceptives (OCs) are the most popular reversible contraceptive method available in the United States. An estimated 10 to 18 million women currently use OCs. ... The reported consistency of OC pill use varies widely among studies.[5-7] A retrospective study ... found that only 42% of OC users said they took a pill every day, and only 20% said they took a pill within 2 hours of the same time every day. Another study[9] reported that 19% of a convenience sample of 6676 European women between the ages of 16 and 30 stated they generally miss one or more pills per cycle. Those who reported missing pills were more than three times as likely to experience an unintended pregnancy than were women who took their OCs consistently. Factors associated with poor compliance included a lack of established routine for pill taking, failure to read and understand written material accompanying the OC package, not receiving adequate information from a health care provider, and the occurrence of side effects, such as nausea and bleeding irregularities. More recently, in a study of 992 women ... 47% of users missed one or more pills per cycle and 22% missed two or more. Women who did not have an established routine for pill taking were nearly four times as likely to miss two or more pills per cycle than were women who did have a routine.