What is the typical failure rate of the pill?

With typical use, the birth control pill is about 93% effective, meaning about 7 out of 100 users get pregnant each year [1.2.1]. Understanding what is the typical failure rate of the pill requires looking at both 'perfect use' and 'typical use' scenarios.

Quick Summary

The birth control pill's effectiveness varies; with perfect use, it's over 99% effective, but with typical use, the failure rate is about 7% [1.2.1, 1.2.3]. This discrepancy is due to factors like missed pills, timing, and medication interactions.

Key Points

• Typical vs. Perfect Use: With perfect use, the pill is >99% effective, but with typical, real-world use, about 7 out of 100 users get pregnant annually [1.2.1, 1.2.3].

• Consistency is Key: The main reason for pill failure is inconsistent use, such as missing pills or taking them at different times [1.3.1].

• Pill Types: Both combination (estrogen and progestin) and progestin-only pills have a similar typical failure rate of around 7-9% [1.2.2, 1.2.5].

• Influencing Factors: Vomiting soon after taking a pill, severe diarrhea, and certain medications (like some anti-seizure drugs and St. John's Wort) can reduce effectiveness [1.3.2, 1.3.3].

• Missed Pill Protocol: If you miss a combination pill, take it ASAP. If you miss two or more, use backup contraception for 7 days [1.4.1]. Mini-pills require a backup method if taken more than 3 hours late [1.5.3].

• Comparison: The pill's typical failure rate (7-9%) is higher than that of long-acting methods like IUDs (<1%) and the implant (<1%) [1.6.2].

• Emergency Contraception: EC can be considered if pills are missed and unprotected sex has occurred, especially in the first week of a pack [1.4.3].

Understanding Birth Control Pill Failure Rates

When discussing the effectiveness of oral contraceptives, it's crucial to understand two key terms: "perfect use" and "typical use" [1.2.6].

• Perfect Use: This refers to the effectiveness of the pill when used exactly as directed in a clinical trial setting—taking it every single day at the same time without error. With perfect use, both combination and progestin-only pills are more than 99% effective, with a failure rate of less than 1% [1.2.2, 1.2.3].
• Typical Use: This reflects how effective the pill is for the average person in the real world. It accounts for human errors like forgetting a pill, taking it late, or other interfering factors. The typical use failure rate for the pill is around 7-9%, meaning about 7 to 9 out of 100 users will become pregnant in a year [1.2.1, 1.2.5].

The gap between these two rates highlights that user consistency is the most significant factor in the pill's success [1.3.1].

Types of Pills and Their Effectiveness

There are two main categories of birth control pills, and their effectiveness rates are generally reported together.

• Combination Pills: These pills contain both estrogen and progestin. They primarily work by preventing ovulation [1.2.5]. With typical use, they are about 93% effective [1.2.2].
• Progestin-Only Pills (Mini-Pill): These pills contain only progestin and work by thickening cervical mucus to prevent sperm from reaching an egg and thinning the uterine lining [1.2.2]. They are also about 93% effective with typical use [1.2.2]. However, they must be taken within the same 3-hour window each day to maintain effectiveness, making them less forgiving of errors than combination pills [1.5.3, 1.5.5]. A newer type of progestin-only pill containing drospirenone allows for a 24-hour window [1.5.6].

Factors That Increase the Failure Rate

Several factors can reduce the pill's effectiveness and increase the risk of an unintended pregnancy:

• Inconsistent Use: Forgetting to take the pill or taking it at inconsistent times is the main reason for failure [1.3.1]. Missing two or more pills significantly increases your risk [1.4.6].
• Vomiting or Severe Diarrhea: If you vomit within two to three hours of taking a pill, or experience severe diarrhea for more than 48 hours, your body may not have absorbed the hormones [1.3.2, 1.9.2]. This should be treated as a missed pill [1.9.5].
• Medication Interactions: Certain medications and supplements can interfere with the hormones in birth control pills, making them less effective. These include:
  • The antibiotic Rifampin (other common antibiotics generally do not affect the pill) [1.3.1, 1.3.3].
  • Some anti-seizure medications (like carbamazepine, topiramate, and phenytoin) [1.8.4, 1.8.5].
  • Certain antiretroviral drugs used to treat HIV [1.8.4].
  • The herbal supplement St. John's Wort [1.3.3].
• Improper Storage: Storing pills in extreme temperatures (too hot or too cold) can potentially degrade the hormones and reduce effectiveness [1.9.3].

What to Do If You Miss a Pill

How you handle a missed pill depends on the type of pill and how many you've missed.

• Missed One Combination Pill: Take the missed pill as soon as you remember, even if it means taking two in one day. You generally do not need backup contraception [1.4.1, 1.4.3].
• Missed Two or More Combination Pills: Take the most recent missed pill as soon as possible and continue with the rest of the pack. Use a backup method, like condoms, for the next 7 days [1.4.1, 1.4.6]. If you had unprotected sex in the previous 5 days, consider emergency contraception [1.4.3].
• Missed One Progestin-Only Pill (Mini-Pill): If you are more than 3 hours late taking your pill, take it as soon as you remember and use a backup method for the next 48 hours [1.4.4, 1.5.3].

Comparison of Contraceptive Failure Rates (Typical Use)

To put the pill's failure rate in context, here is how it compares to other common contraceptive methods.

Method	Typical Use Failure Rate (%)
Implant	0.1% [1.6.2]
Hormonal IUD	0.7% [1.6.2]
Copper IUD	0.8% [1.6.2]
Sterilization (Female)	0.5% [1.6.2]
Vasectomy (Male)	0.15% [1.6.2]
Injectable (Shot)	4-6% [1.6.1, 1.6.2]
Birth Control Pill	7-9% [1.6.1, 1.6.2]
Vaginal Ring	7-9% [1.6.1, 1.6.2]
Patch	7-9% [1.6.1, 1.6.2]
Male Condom	13% [1.6.2]
Withdrawal ("Pulling Out")	20% [1.6.2]
Spermicide	28% [1.6.2]

Conclusion

The birth control pill is a highly effective method of contraception when used correctly and consistently. The difference between its perfect use failure rate of less than 1% and its typical use failure rate of around 7-9% underscores the critical importance of user adherence [1.2.1, 1.2.5]. By taking the pill at the same time every day, understanding what to do if a dose is missed, and being aware of potential drug interactions, users can significantly decrease the risk of unintended pregnancy and get closer to the perfect use effectiveness rate.

For those who find a daily routine challenging, long-acting reversible contraceptives (LARCs) like the IUD or implant offer higher typical-use effectiveness because they remove the element of user error [1.2.5].

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For more information, consult a healthcare provider or visit Planned Parenthood.

Frequently Asked Questions

Can I get pregnant if I miss one birth control pill?

If you miss one combination pill, the risk of pregnancy is minimal if you take it as soon as you remember [1.4.3]. For progestin-only pills, if you are more than 3 hours late, you should use a backup method for 48 hours as the risk increases [1.5.3].

Does vomiting or diarrhea affect the pill's effectiveness?

Yes. If you vomit within 3 hours of taking a pill or have severe diarrhea for more than 24-48 hours, the pill may not have been absorbed properly. You should treat it as a missed pill and use a backup method of contraception [1.3.2, 1.9.4].

Which medications are known to interfere with birth control pills?

Certain medications can lower the pill's effectiveness. These include the antibiotic Rifampin, some anti-seizure drugs (like carbamazepine and topiramate), certain HIV medications, and the herbal supplement St. John's Wort [1.8.4, 1.8.5].

Is the mini-pill (progestin-only pill) less effective than the combination pill?

With typical use, both the mini-pill and the combination pill have a similar effectiveness rate of about 93% [1.2.2]. However, the mini-pill is less forgiving and must be taken within a strict 3-hour window each day to be effective [1.5.3].

How soon is the pill effective after starting it?

If you start combination pills within 5 days of your period starting, you're protected immediately. Otherwise, it takes 7 days. Most progestin-only pills take 2 days to become effective [1.3.5, 1.7.3].

Do birth control pills protect against Sexually Transmitted Infections (STIs)?

No, birth control pills do not protect against STIs. Barrier methods like condoms are necessary to reduce the risk of STI transmission [1.2.2].

What is more effective at preventing pregnancy, the pill or an IUD?

The IUD is significantly more effective with typical use. The failure rate for hormonal IUDs is around 0.7% and for copper IUDs is 0.8%, compared to the pill's typical failure rate of 7-9%. This is because IUDs eliminate the risk of user error [1.6.2].