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The pill, the IUD, the ring, the implant, and the patch falling into a hole.

Illustration by Marta Pucci

Sex

Why does hormonal birth control fail?

Birth Control 101

by Sarah Toler, Science Writer for Clue Reviewed by Laurie Ray, Science Writer at Clue
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Top things to know

  • Hormonal birth control (HBC) usually works when used correctly and consistently 

  • Unintended pregnancies are declining because of increasing access to effective contraception

  • Human behavior can play a part in HBC being less effective. The effectiveness of any method depends on typical vs. perfect use. 

  • Tracking your HBC in Clue can help you prevent failure

Most of the time, hormonal birth control doesn’t fail. When people use hormonal birth control consistently and correctly, pregnancy occurs in only 0.05 percent to 0.3 percent of people (depending on the method) over a year of use (1). (Compare that to the eighty-five percent of people who become pregnant within a year, when not using birth control.)

Almost half of pregnancies are unintended, but this number is declining, likely because of the increasing availability of highly effective methods of birth control (2). 

If birth control is so effective, why do we hear so many stories about people becoming pregnant while using it? Generally, it’s because as humans, we are more flawed than the medical technology of birth control. 

When we talk about birth control and why certain methods fail, it’s important to make a distinction between perfect use and typical use (1).

  • Typical use reflects how people actually use a type of birth control, even if they use it inconsistently or incorrectly.

  • Perfect use reflects how effective the form of birth control is if used exactly as prescribed (3).

While certain behaviors can put a person at risk for birth control failure, there are times when birth control fails without a real reason and without anyone to blame. Contraception is a modern technology, and no technology is perfect (1). 

Why hormonal birth control fails

Hormonal birth control works to prevent pregnancy by stopping ovulation and/or, thickening cervical mucus (1, 4). Human behavior is commonly a factor in why these methods fail. Below, we address the different hormonal birth controls, and factors that may cause them to fail, in greater depth. 

The pill

Failure rate: 9% typical use, 0.3% perfect use (1)

Human behavior is the most common reason that birth control pills fail (1). The majority of people using the pill forget to take one or more each month (5), while others have challenges filling the prescription monthly (6). Some people might stop taking it because they are concerned about side effects (1). 

Taking medications like certain antibiotics, some anticonvulsants, and the herb St. John’s Wort can make the pill less effective (7, 8). Prolonged vomiting or diarrhea can prevent absorption of the pill and lead to pregnancy if a backup method isn’t used (9). 

The patch

Failure rate: 9% typical use, 0.3% perfect use (1)

The patch contains hormones like the pill, but it sticks to the skin (1). The patch can fail if it detaches and isn’t replaced, or if the patch isn’t replaced weekly (1).

The ring

Failure rate: 9% typical use, 0.3% perfect use (1)

The ring is inserted into the vagina to deliver hormones (1). The ring can fail if it’s withdrawn accidentally during sex, when using a tampon, or having a bowel movement and not reinserted within three hours (1). It could also fail to prevent pregnancy if the same ring is used for more than four weeks (1).

The shot

Failure rate: 6% typical use, 0.2% perfect use (1)

The shot contains a progestin (a synthetic form of progesterone) that lasts three months (1). It can fail if a person doesn’t receive their next dose in time, or if it is given incorrectly (10).

The implant

Failure rate 0.05% typical use, 0.05% perfect use (1, 11)

Hormonal implants are thin rods that are inserted under the skin in the upper arm (1). Although the implant is one of the most effective forms of birth control (1), it can fail if it’s not correctly inserted or if a person is taking antiepileptic drugs (12). 

Why IUDs fail

Hormonal IUD

Failure rate: 0.2% typical use, 0.2% perfect use (1)

Intrauterine devices, or IUDs, are small implants placed inside the uterus. While the hormonal IUD thickens cervical mucus and sometimes prevents ovulation like other hormonal birth control methods, the presence of the IUD inside the uterus also causes inflammation that is toxic to both sperm and eggs (1).

An IUD can fail if it is not placed correctly by the healthcare provider, or if it’s expelled from the uterus (1). All human anatomy varies slightly from person to person, and uteruses come in a variety of shapes, sizes, and positions. Someone with a uterus that is smaller than average, shaped or positioned atypically may be more at risk for IUD failure because if the device is not in the appropriate position, it may be less effective or be more likely to be expelled (13).

While the copper IUD does not contain hormones, we’ve included its failure rates here for comparison and clarity.

Copper IUD 

Failure rate: 0.8% typical use, 0.6% perfect use (1, 11)

How to prevent your birth control from failing

1. Use two birth control methods simultaneously (1).

No, this doesn’t mean using two condoms at once. It means pairing a hormonal method with another method that doesn’t involve hormones but is still effective at preventing pregnancy. Some good options are condoms, spermicides, or withdrawal.

2. If you’re on the pill and need a reminder to take it, Clue can send you a birth control pill reminder notification. You can also track when you take your pills.

If you miss a pill and don’t know what to do, Clue can walk you through the difference between a taken, late and missed pill and let you know what your next step should be. 

Choosing a birth control method is an important decision, but just because one method is the most effective doesn’t mean it’s the most effective for you

While pills have prevented millions of pregnancies, they won’t work if you know you’re not good at remembering to take them every day.

A hand holding a phone with the Clue app opened

Download Clue to send a daily reminder to take your pill.

3. Explore options that don't require daily effort.

The patch is a good option for many people because you only need to remember to change it once a week. Applying it is usually pretty easy, but if you use a lot of creams, lotions, or sunscreens, it might not adhere well. You’ll need to make sure your skin is clean and dry before attaching the patch and pressing it for ten seconds. Then, make sure all of the edges are stuck to the skin—peeling edges can cause the patch to be pulled off (1). 

The ring also needs to be changed infrequently. If you don’t have trouble remembering to change it each month, you just need to remember to check that it’s still inserted after sex, tampon use and bowel movements. 

IUDs and the implant have the lowest risk for human error, since you don’t have to worry about taking them or changing them frequently, but they can be inserted incorrectly by the healthcare provider, or expelled after the fact. After your IUD or implant is inserted, you can ask your healthcare provider to show you how to feel for it to know it’s there—then make sure you check it regularly. 

If you’re having trouble using your birth control correctly and consistently, talk to your healthcare provider about trying a new option.

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