Pill-taking mistakes are not unique to OC users. Research on medication-taking habits for a number of illnesses—from epilepsy to asthma—indicates that 10% to 20% of patients have trouble taking correct doses, whether they underuse, overuse, or use their medications inconsistently (146).

Common problems with OC use include missing pills, taking “rests” from pill use, running out of pills, incorrectly switching from one pill packet to the next and so extending the amount of time without taking hormonal tablets, and taking pills out of sequence. Family planning programs can address many of these problems.

Missing pills. Many women may miss a few pills in a packet and not take corrective action. Sometimes women simply forget to take a pill now and then. Some women may miss a few pills because their supply runs out or because they leave their pills at home when they travel. Women may skip pills because they are experiencing side effects, such as nausea or spotting, and think—mistakenly—that skipping a few pills will reduce these side effects.

Missing a pill now and then seldom leads to pregnancy (see side-bar, Missed Pills and Pregnancy: When are Women Most at Risk?). Frequently missing a number of pills, however, increases a woman's chances of becoming pregnant. Furthermore, missing pills in each pack without becoming pregnant can be self-reinforcing. Some women who miss pills may begin to think that their irregular pill-taking pattern is good enough to avoid pregnancy and thus continue taking the pill haphazardly (129, 165).

Eventually, some women will lose this gamble. A study in Western Europe, for example, found that women who usually missed one or more pills from each packet were nearly three times more likely to become pregnant than women who reported not missing any pills (182).

Although missing pills increases a woman's risk of unintended pregnancy, women who do not use the pill perfectly still have a lower overall risk of pregnancy than women who use no contraception at all. In a US study only 13% of pill users took their pills correctly over a period of 6 to 12 months. Nevertheless, the pill users overall experienced only one-third the rate of pregnancy that occurred among women who had obtained pills but did not use them at all (148).

Women can benefit from instructions on how to make up missed pills. Women who miss one pill should take the missed pill as soon as they remember. Women missing two or more pills can protect themselves from pregnancy by following the “seven-day” guideline (see side-bar, Using the “Seven-day” Guide Line to Make Up Missed Pills).

Few studies have looked at what corrective action women take when they miss pills. A 1997 study of 103 US women's pill-use habits over three cycles found that 52% did not miss more than one pill. Among women missing more than one pill, some 18% avoided intercourse for a week thereafter, while 3% used a back-up method for seven days after missing pills. Either abstinence or a back-up method would be effective if kept up until a woman had taken hormonal pills for seven days straight. Some 27%, however, did not take any protective action after missing multiple pills (147).

Taking “rests” from pill use. Sometimes women stop taking their pills temporarily. Some health care providers incorrectly advise pill users that they need to give their bodies a “rest period” from the pill. For example, a 1993 study in Jamaica found that two-thirds of private providers recommended a rest from pill use in order to “expel” chemicals from the body (80).

Many women also believe that they need to give their bodies a rest from the pill. In an Egyptian study 13% of self-identified pill users who had no pills on hand when interviewed said that they were resting from the pill hormones. Nearly 20% of women with pill packets at home at the time of interview reported not taking a pill in the last eight or more days because they were resting from the method (129). In Australia some 27% of OC users interviewed reported taking a rest from pill use at some time (237).

Resting from the pill is a common practice around the world, and yet there is no scientific justification for it. There is no accumulation of hormones in the body when taking OCs (55, 220). Nor are there any known health or fertility benefits to taking periodic rests. In contrast, the risks can be considerable. In one study 25% of women who took such rests from pill use became pregnant unintentionally (75).

Making transition errors. Some pill users do not begin a new pill packet at the right time (94, 123, 164, 212). Making this kind of mistake—a transition error—is common. In Bangladesh, for example, although most women correctly answered questions about how to take pills and how to make up for missed pills, only 37% of rural users and 24% of urban users knew when to begin their next 28-day packet (123).

The 28-day pill packets allow users to take a pill every day, rather than having to count seven pill-free days before starting a new 21-day packet. It would seem that taking a pill every day would be easier to remember than counting days between cycles. Nevertheless, a study in Egypt found that users of 21- and 28-day packets made transition errors equally often (94).

Some women incorrectly wait for a withdrawal bleed, which they perceive as menstruation, before starting the next pill packet. In Bangladesh, for example, 47% of rural woman and 59% of urban women surveyed said that they waited for evidence of menstruation between pill packets (123). Women with misperceptions about the pill—in particular, the incorrect idea that OCs can cause infertility (1, 150)—may wait for what they think is a menstrual period as evidence that the pill has not affected their ability to have children (100). This misperception can extend the interval between pill packets. The correct practice is to start the next cycle of pills on schedule—no later than seven days after the last hormonal tablet—regardless of when withdrawal bleeding does or does not occur.

Taking pills out of sequence. Some women do not take their pills in the correct order. Rather than follow the arrows on the packet that indicate which pill to take next, some women take pills in random order or follow the rows in a different direction. A study in Egypt found that 24% of women who could show the interviewer their pill packets had taken pills out of sequence, while in Indonesia 5% had made this mistake (94). With 28-pill packets, taking pills out of sequence can result in taking placebo pills at the wrong time in the pill cycle, increasing the risk of pregnancy.