In this article, we look at how effective the birth control pill is, and five reasons why the pill might fail. We also give tips on how to prevent pill failure and describe some early signs of pregnancy.
How effective is the pill?
Certain circumstances can reduce the effectiveness of birth control pills.
The combined pill contains hormones that prevent ovulation, which is when the ovaries release an egg for fertilization. Another type of pill, known as the minipill, causes a person's cervical mucus to thicken and the uterine lining to thin, which reduces the likelihood of sperm reaching an egg.
The birth control pill is very effective if a person takes it correctly and does not miss any pill days. According to the Centers for Disease Control and Prevention (CDC), the pill is 99.7 percent effective with perfect use. This means that less than 1 out of 100 women who take the pill would become pregnant in 1 year.
However, with typical use, the effectiveness of the pill is 91 percent. This means that around 9 out of 100 women would become pregnant in a year of taking the pill.
Five reasons for pill failure
Although the birth control pill is generally very effective, some situations can reduce its effectiveness and may sometimes result in unintended pregnancies. These include:
Missing a day
Manufacturers intend for people to take the pill daily for it to be most effective. If a person misses a day, their hormone levels may not remain at consistent enough levels to prevent pregnancy.
If a person finds it difficult to take the pill on a daily basis, other birth control methods may better suit their needs. A doctor or gynecologist can advise on the range of alternative contraceptives.
Sometimes a person may be ill when they take the pill. When a person vomits, the pill can come back up, or they may not fully absorb it into their body.
Anyone who experiences vomiting shortly after taking the pill should take another pill as soon as possible and then take their next pill as usual.
Not taking the pills at the same time each day.
In addition to taking birth control pills daily, a person should also take the pills at around the same time each day. This can maintain their hormone levels more consistently.
A person should always take the minipill within the same 3-hour time window every day. Someone who misses their window should use a backup birth control method for the next 2 days or avoid having sex.
Many people set a daily alarm reminding them to take their pill at the correct time each day.
Not starting a new pack right away
Some medications and supplements can interact with the pill and decrease its effectiveness.
It is essential to start a new pack of pills the day after finishing the previous one. However, sometimes a person may not have their new package yet. Missing a few days between packs can make the pill less effective at preventing pregnancy.
According to the CDC, anyone who misses two or more pills in a row should use a backup contraceptive method or avoid sexual intercourse until they have taken the birth control pill for 7 consecutive days.
Medications that interfere with the pill
Some medications can make the pill less effective. Medications include certain antibiotics, such as rifampicin, and anti-fungal drugs, such as griseofulvin.
A person should use backup contraception while taking these medications and for 48 hours after finishing the course.
Other more long-term medications and supplements may also affect how well birth control pills work. These can include:
- epilepsy drugs, such as phenobarbital, phenytoin, and carbamazepine
- anti-viral medications used to treat HIV
- St. John's Wort, which is a herbal remedy
Tips for preventing pill failure
Birth control pills are very effective if a person takes them correctly and does not miss any pill days. The following tips can help prevent unintended pregnancies while taking the pill:
- reading the packaging and following the instructions carefully
- taking the pill at the same time every day
- using an app that tracks periods and provides pills reminders, such as one of the apps from our review article
- always getting a new pill pack at least 1 week before the last pill pack is due to run out
- always taking missed pills as soon as possible
- using a backup method of contraception, such as a condom, if a person misses taking two or more pills in a row
If a person is concerned about not being able to take their pills consistently, they should speak to their doctor or gynecologist about other birth control methods. There are several options available that do not require taking a pill daily, such as an intrauterine device, or IUD.
Early signs of pregnancy
Unexplained tiredness can be an early sign of pregnancy.
If a person is concerned about contraceptive failure and the possibility of being pregnant, they should speak to their doctor. However, there are also some early signs that can indicate pregnancy:
- Bloating. While bloating is often a symptom of premenstrual syndrome, it can sometimes also be a sign of early pregnancy.
- Breast tenderness. Raised levels of the hormones estrogen and progesterone can cause breast tenderness early in pregnancy. Some women may also experience symptoms, such as tingling, heaviness, or feelings of breast fullness.
- Light spotting. A small amount of bleeding or spotting can occur when an egg attaches to the uterine lining. If spotting occurs outside of an expected menstrual cycle, it may be an early symptom of pregnancy.
- Unexplained fatigue. Hormonal changes that occur in the body during pregnancy can make a person feel tired, even during the early stages.
- Urinating more often. Hormonal changes can increase a woman's need to urinate during early pregnancy.
Anyone who thinks they could be pregnant may wish to take an at-home pregnancy test. These tests have become more sensitive to a person's hormone levels and better at detecting pregnancy in its earliest stages.
However, at-home pregnancy tests still may not reliable if an individual takes it too early or does not follow the instructions correctly. According to the United States Food and Drugs Administration (FDA), for most reliable results, a person should take the test 1–2 weeks after their first missed period.
While birth control pills are generally very effective, they can sometimes fail to prevent pregnancies if a person does not use them correctly and consistently.
Anyone who is concerned about the effectiveness or convenience of their method of contraception should speak to a doctor.
If a person misses taking more than one pill, they should use a backup contraceptive method for at least 7 consecutive days of retaking the pill.