Nobody’s perfect: Pill efficacy for the real world

Our patients shouldn’t have to be perfect to protect themselves from accidental pregnancy.

by Colleen Krajewski, MD, MPH

published 04/02/16

It’s no secret that many women’s health care providers use IUDs, likely because they have the highest efficacy and continuation rates. But the most common method of birth control among our patients remains the pill. The pill is advertised as having 99% efficacy, but in real life we know that about it’s closer to 90%. That means about one in 10 women will have an unplanned pregnancy while using this method. How can the advertised number and real life numbers be so different? And what can we do to help our patients narrow the gap between these numbers?

Advertised numbers = “perfect use”

The advertised figures, also known as “perfect use” numbers, come from clinical trials of the method sponsored by the pharmaceutical companies making the product. The patients in these clinical trials are carefully screened; those with even minor medical problems or who use other medications are excluded. These patients are highly motivated to avoid pregnancy, are being financially compensated for being in the study, and have frequent contact with study coordinators. This is why the term “perfect use” really doesn’t tell the whole story. It implies that it’s possible for a patient to replicate these efficacy rates in real life. I prefer to use the term “theoretical use.” I tell my patients: “It’s possible in theory for the methods to work that well, but that’s not usually the case.”

Real-life numbers = “typical use”

The real life numbers, also known as “typical use” numbers, come from nationally representative surveys of women in the United States. These surveys take a sample from the entire country, include a wide variety of women, and answer the question: “What percentage of couples will become pregnant while using these methods over the course of one year?” This is much more applicable to my patient’s daily lives. I prefer to use the term “real life” efficacy to describe these numbers.

Why is the theoretical different from real life pill efficacy?

Another way to ask this question is: “Why do women using the pill in the real world have a lower efficacy than those paid to be in research studies?” There are multiple possible answers, and patients have some common misconceptions about this.

Here are some of the reasons that the pill may not work as advertised:

  • Didn’t start a new pack on time. Maybe the pharmacy was closed, or she just couldn’t get to the pharmacy, or she forgot to pick up a new script, or her insurance changed, or her refill order expired… You get the idea.

  • Skipped more than one pill. Maybe she had something stressful disrupt her daily routine, or didn’t bring the pack while away from home, or she just plain forgot.

  • Had another health issue that interfered with absorption. Maybe she had vomiting due to food poisoning or a hangover, or diarrhea from a course of antibiotics.

  • Took another medication that made the pill less effective. While this is less common, there are medications that interfere with the pill.

  • Lost the pill pack. It could be an accident like putting pills through the wash, or she could have a partner who interferes with her birth control.

Here are some of the misconceptions I hear from patients about why the pill doesn’t work as advertised:

  • “I took the pill a few hours late.” While taking the combination pill every day is an important part of its efficacy, being a few hours off schedule does not meaningfully reduce its efficacy.

  • “I had to take antibiotics that messed with the pill.” Most antibiotics don’t directly affect the pharmacokinetics of the pill. The only exception is rifampin, which is rarely used in the U.S.

Because there are various factors affecting women’s ability to attain theoretical efficacy, we can’t predict which will happen to a specific patient.

Narrow the gap

Here are some things you can do to help narrow the gap between theoretical and real world efficacy:

  • Prescribe more than one month of pills at a time. If you write a prescription for 365 days, your patient can get access to 13 packs at once. Research shows that having a year’s supply substantially increases continuation and reduces unintended pregnancy. You can also write a 3 month prescription with four refills (Disp ##3, Refill ##4) which is a total of 15 months of coverage.

  • Offer advance provision of emergency contraception (EC) and a back-up method like condoms to all your birth control patients.

  • Talk with patients about the ways that pill formulations may affect efficacy. Formulations with fewer placebo pills or ones designed for continuous use may improve efficacy.

  • Make sure patients know about other methods, especially those whose theoretical-use efficacy and real-life efficacy are basically the same, like IUDs and the implant.

Here are some things your patient can do:

  • Keep the pill packet someplace where she’ll see it every day. This could be next to a toothbrush, the coffee machine, or next to her wallet or transit pass in her bag.

  • When trouble strikes, double up with condoms. We can never predict when food poisoning may hit, or when stress may result in a missed pill—and condoms are an essential back up method for the next seven days.

There are lots of benefits to using the pill, including lighter periods, clearer skin, fewer ovarian cysts, reduced menstrual pain, and a long-lasting reduction in the risk of uterine cancer. Whatever reason a patient has for using the pill, I like equipping her with multiple tools to help her succeed.

Colleen Krajewski is an assistant professor at the University of Pittsburgh, where she specializes in family planning. She has a special interest in contraception for women with high risk medical conditions and the role of the internet in shared decision making between patients and doctors. She's a VERY proud dog mommy, and was the captain of the winningest skeeball team in Baltimore during her time there.
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