10 Reasons You Might Get Pregnant on the Pill — And What to Do Immediately

If you’re taking birth control pills and worried you might be pregnant, you’re not alone — it’s a more common concern than you’d think.

According to the CDC, about 9 out of 100 women on the pill get pregnant each year with typical use. When taken exactly as directed, birth control pills are 99% effective in preventing pregnancy.

This article walks you through 10 real reasons that might explain why, even if you’re on the pill, pregnancy can still happen.

We’ll also cover what steps to take right away if you're unsure. Clear, honest, and backed by facts — this guide is here to help you understand what’s happening and what to do next.

How Birth Control Pills Work to Prevent Pregnancy (Most of the Time)

So, you’re taking birth control pills and wondering how they actually stop pregnancy. Let’s break it down in the simplest way possible. Birth control pills work by using hormones — usually estrogen and progestin — to do three main things:

• Stop ovulation: That means no egg is released.
• Thicken cervical mucus: This blocks sperm from getting to the egg.
• Thin the uterus lining: So a fertilized egg can’t attach easily.

There are two main types: combination pills (with estrogen and progestin) and progestin-only pills (also called mini pills). Both are safe and work well, but you have to take them the right way.

Dr. Lisa Stern, an OB-GYN, discusses various method of birth control:

“Even if you're doing everything right, no birth control option is 100% perfect — not even the pill.”

While birth control pills prevent pregnancy, they do not protect against sexually transmitted infections; using condoms can provide additional protection.

Not All Pills Work the Same: Combination Pills vs. Progestin-Only Pills

Watch for These Early Signs That Could Mean Pregnancy

1. Missed Pill or Inconsistent Use

If you miss a pill or don’t take it at the same time every day, it lowers the pill’s power to prevent pregnancy. That’s true for combination pills and progestin-only pills.

Progestin-only pills must be taken at the same time every day to prevent pregnancy, within a three-hour window. Forgetting just one active pill can raise your chances of early pregnancy.

Dr. Susan Robinson, OB-GYN at UCSF, says: “Missing two or more pills in a row is the top reason we see pill failures.”

What to do:

• Take your missed pill as soon as you remember.
• Set a reminder or mark your pill packs to stay consistent every day.
• Use a backup method (like barrier methods) for the next 7 days if you missed two or more pills.
• Recent research suggests that adherence to daily pill schedules significantly improves contraceptive effectiveness.

2. Medication Interference or Digestion Issues

Some medications mess with how the pill works in your body, and they may not protect you from sexually transmitted diseases. Some medications and medical conditions can change how birth control pills affect your hormone levels.

Things like St. John’s Wort, certain antibiotics, and seizure drugs can stop the pill from being absorbed right. Diarrhea and vomiting can do the same thing.

The American College of Obstetricians and Gynecologists reports that even clinical pharmacology confirms drug interactions reduce pill effectiveness.

What to watch for:

• Did you take any new medications lately?
• Have you had tummy troubles within 2 hours of taking the pill?

What to do:

• Always check with your doctor about new meds.
• Use a backup method if you had stomach issues.

3. Vomiting, Diarrhea, or Absorption Problems

If your body can’t absorb the pill, it may not work. Throwing up or having diarrhea soon after taking your dose may mean your body didn’t get the full dose of hormones.

What this means for you:

• It could feel like you’ve taken the pill, but your hormone levels never rose high enough to stop ovulation.
• You may still be at higher risk of pregnancy, especially if you had unprotected sex that week.

Quick tip:

• If vomiting happens within 2 hours of taking your pill, count it as a missed dose and take another pill if possible.
• Keep track of symptoms like breast tenderness, light bleeding, or feeling more tired than usual — these could be early signs of pregnancy.

4. Unusual Spotting or Implantation Bleeding

Hormonal birth control pills can also cause spotting, nausea, or mood swings as your body adjusts.Spotting between periods can be totally normal when you're taking birth control pills — especially if you're using progestin-only pills or mini pills.

Birth control pills can cause side effects such as spotting, weight changes, and headaches. But if the bleeding looks different, it might be a sign.

What to look for:

• Light pink or brown bleeding outside your normal cycle
• A small amount of bleeding when your period isn’t due

This could be implantation bleeding, which happens when a fertilized egg attaches to the uterus. It’s usually lighter than a normal period and doesn’t last long.

“Implantation bleeding is often mistaken for a light period,” says Dr. Kate White, OB-GYN and author of Your Guide to Miscarriage and Pregnancy Loss.

Important Tip: If you're unsure whether it’s normal breakthrough bleeding or something else, take a pregnancy test and talk to your healthcare provider.

5. Breast Tenderness or Nipple Changes

Sore or sensitive breasts are common in early pregnancy, but they can also be linked to concerns about breast cancer.

Hormone shifts can make your breasts feel fuller or more painful — even if you're still taking the pill. Breast tenderness is a common side effect when starting birth control pills, and it often decreases over time.

What you might notice:

• Tingling or sharp soreness in the nipples
• Breasts feel heavy, swollen, or extra sensitive to touch
• Some users report mild side effects like bloating or gain weight while on the pill, though it's usually temporary.

This can also happen as a side effect of active pills, but it usually goes away quickly. If it doesn’t, it might be worth checking. Consulting a healthcare provider can help you choose the right pill that aligns with your health needs and lifestyle.

What to do:

• Keep track of changes in your body
• If this symptom comes with others like light bleeding or fatigue, it might be time to take a pregnancy test

6. Fatigue That Hits Out of Nowhere

Feeling tired all the time? Like really tired — even if you slept eight hours? That could be one of the very first signs of unplanned pregnancy. That could be one of the very first signs of early pregnancy.

Your body is using more energy to support a possible pregnancy, even if you're on combination pills or low-dose pills. Mood changes, including depression, have been reported by individuals taking birth control pills due to hormonal fluctuations.

A study published in the Journal of Women's Health found fatigue was reported as an early sign of pregnancy in 78% of women.

What to try:

• Stay hydrated and eat balanced meals
• If the fatigue continues or gets worse, speak to your doctor and consider taking a test

7. Nausea or Food Aversions

Have you noticed certain foods suddenly make your stomach turn? That’s not just in your head.

What to look for:

• Feeling sick to your stomach, especially in the morning
• Suddenly hating the smell or taste of foods you normally enjoy
• Avoiding meals or snacks because they seem “off”

A study by the National Institutes of Health found that up to 80% of pregnant women experience nausea or food aversions in early pregnancy.

Why it matters: Hormone changes triggered by a fertilized egg can cause nausea — even if you're on hormonal contraceptives like combination pills or progestin only pills. If you feel different and you're taking the pill, this is a good reason to take a pregnancy test.

8. Cramping Without a Period

Mild cramping can feel like your period is about to start — but then nothing happens.

Signs to notice:

• Cramps with no bleeding
• Cramps at a weird time in your cycle
• Cramps that are lighter or sharper than usual

These might mean the fertilized egg implants in the uterus. While it’s normal to have some cramps during your cycle, implantation cramps are often missed or confused for PMS.

9. Super Sensitive to Smells

Does your partner’s cologne or last night’s leftovers suddenly smell too strong? That could be another early clue.

What people report:

• Strong reaction to smells that never used to bother them
• Feeling dizzy or queasy around perfumes or cleaning products
• Sense of smell feels way more intense

This happens because hormone levels are shifting, and it often shows up before you even miss a pill or skip a period. It can make you feel uncomfortable in situations that used to feel normal.

10. Mood Swings That Feel Off the Charts

Everyone gets grumpy now and then. But if your moods feel all over the place lately, it could be one of the early signs that you’re pregnant on the pill.

What this might look like:

• Feeling super happy one minute and really sad the next
• Crying at small things, like a commercial or song
• Getting irritated by stuff that never used to bother you

This happens because of hormone level changes, especially early on when a fertilized egg has implanted. Even when you’re taking birth control pills, unexpected hormone shifts can happen — especially if you're taking the pill irregularly or if certain medications are interfering.

What to Do If You Suspect You’re Pregnant on the Pill

Finding out you might be pregnant on the pill can be confusing, even scary. Most of the time, pregnancy starts normally. But in rare cases, it could be something more serious — like an ectopic pregnancy.

The CDC notes that progestins taken in early pregnancy slightly increase the risk of hypospadias in male babies, but this is related to a different context than standard birth control pill use.

When It's Not Just a Regular Pregnancy: Understanding Ectopic Pregnancy

An ectopic pregnancy happens when a fertilized egg attaches somewhere outside the uterus — usually in the fallopian tube. This type of pregnancy cannot continue and can be dangerous if not treated early.

Even if you're taking birth control pills, this can still happen. No method is perfect.

"Ectopic pregnancy can cause severe pain and bleeding. It’s one of the first things we rule out when someone calls in worried they’re pregnant despite using birth control,” says Dr. Naomi Jacobs, OB-GYN, Mount Sinai Health System.

Signs to Watch For:

• Sharp or stabbing pain in your lower belly
• Light vaginal bleeding that seems “off”
• Shoulder pain or dizziness
• Feeling weak or faint

What to Do Next:

• Call your healthcare provider right away
• Don’t try to “wait it out” — early action matters
• Tell them you’re on birth control pills and think you could be pregnant
• Ask for an ultrasound to confirm the pregnancy location

Expert Help You Can Trust: Meet Dr. Anshu Agarwal in Ranchi

If you're navigating concerns about birth control effectiveness or suspecting pregnancy while on the pill, consulting a seasoned gynecologist can provide clarity and peace of mind. Dr. Anshu Agarwal, based in Ranchi, Jharkhand, offers comprehensive women's health services tailored to individual needs.​

Why Choose Dr. Anshu Agarwal?

• Extensive Experience: With over 18 years in gynecology and obstetrics, Dr. Agarwal has managed a wide range of cases, from routine check-ups to complex fertility issues.​
• Specialized Services: Her expertise encompasses high-risk pregnancies, laparoscopic surgeries, and infertility treatments, emphasizing solutions that often avoid the need for IVF.​
• Patient-Centric Approach: Dr. Agarwal is known for her compassionate care, ensuring patients feel heard and supported throughout their health journey.​

Clinic Details:

• Location: Medifirst Hospital, SubPlot No.2703/1 and 2703/2, Plot No. 2703, Booty Rd, near Suryodaya Apartment, Bariatu, Ranchi, Jharkhand 834009​
• Contact: Phone: 072939 37999​
• Website: www.dranshuagarwal.com​

When to Consult:

• If you've missed birth control pills or taken them irregularly.​
• After experiencing symptoms like unusual bleeding or persistent fatigue.​
• When considering alternative birth control methods or planning a pregnancy.​

Dr. Agarwal's clinic offers a supportive environment to discuss your concerns and explore the best options for your reproductive health.

Can Birth Control Pills Harm an Early Pregnancy?

If you’re pregnant on the pill, it’s normal to worry: Did taking the pill hurt the baby? The short answer is: Probably not. Most experts, including the American College of Obstetricians and Gynecologists (ACOG), agree that taking birth control pills early in pregnancy is unlikely to cause birth defects.

Why? Because the hormones in pills are low-dose and designed to prevent ovulation. They’re not meant to support pregnancy, but they don’t usually stop it once it begins.

Experts continue to research if there's a link between hormonal contraceptives and preterm birth, especially with unplanned pregnancies.

“We don’t recommend continuing the pill once pregnancy is confirmed, but there’s no evidence it causes harm if taken unknowingly,” says Dr. Lena Chavez, OB-GYN at NYU Langone.

Some studies explore whether early pregnancy while on the pill could raise the risk of low birth weight, though results are not conclusive. Though rare, oral contraceptives have been linked to a slightly higher risk of blood clots, especially in smokers or women over 35.

Certain Medications That Can Make Your Pill Fail

When Pills Aren’t Right for You: Consider Alternative Birth Control Options

The right type of birth control depends on your lifestyle, health history, and how consistently you can take it. Sometimes, the oral contraceptive pill just doesn’t work well for your body.

If you’re pregnant on the pill or struggling with side effects, don’t worry — there are other birth control options that might be a better fit.

Why Pills May Not Be Right for You

• You forget to take them every day
• You’re on certain medications (like John’s Wort) that make the pill less effective
• You’ve had bad side effects like mood swings, nausea, or weight gain
• You want a long-term or non-hormonal solution

Safer, Smarter Options to Prevent Pregnancy

Here are other birth control methods that don’t involve a daily pill:

• Barrier methods: Like condoms or diaphragms — no hormones, easy to use
• IUDs: Tiny devices placed in the uterus — very effective and low maintenance
• Implants or shots: Great for long-term use and hormonal methods that you don’t have to think about daily
• Fertility awareness: Tracking your cycle and avoiding sex during fertile days (takes practice!)
• Permanent options: Like tubal ligation (for those sure they’re done having kids)

Emergency Contraception and Backup Methods You Can Trust

Emergency contraception is also known as the “morning-after pill.” It works best when taken within 72 hours of unprotected sex or a birth control slip-up. It stops the fertilized egg from attaching to the uterus.

“Emergency birth control doesn’t end a pregnancy. It only helps with pregnancy prevention before implantation,” says Dr. Tasha Young, women’s health specialist at the Mayo Clinic.

There are two main types:

• Levonorgestrel pills (like Plan B) — available over the counter
• Ulipristal acetate (Ella) — prescription only

FAQs

1. Can Birth Control Pills Cause Birth Defects If You Conceive?

This is a common worry for anyone who becomes pregnant on the pill. The good news? Research says no. According to the American College of Obstetricians and Gynecologists, there’s no strong link between using birth control pills early in pregnancy and birth defects.

2. Do Barrier Methods Work Better When Combined with Birth Control Pills?

Yes — especially for pregnancy prevention during typical use. If you forget or skip active pills, using barrier methods (like condoms) adds extra protection. It’s also smart to use them during the week you’re on placebo pills, just in case you ovulate early.

Inactive pills in your pack are hormone-free and meant to keep your routine, but they don’t protect against pregnancy

3. How Soon Should I Take a Pregnancy Test If I Suspect Birth Control Failure?

If you had unprotected sex, missed pills, or are feeling unusual early signs, wait at least 10–14 days to take a pregnancy test. Testing too early can give a false result. If you’re unsure, test again after a few days. Always check with your doctor if you get a positive result.

4. Can You Get Pregnant While Taking Active Pills?

Yes, though it’s rare, there is an increased risk of pregnancy when not used correctly . With perfect use, birth control pills are over 99% effective, but with typical use, that drops to 91%, according to the CDC.

Reasons you might still get pregnant:

• You missed pills
• You're on certain medications (like John’s Wort)
• Your body didn’t absorb the pill due to vomiting or diarrhea
• Engaging in sexual activity without consistent contraceptive use increases the risk of unintended pregnancy.

If you're worried, use a backup method and speak with your doctor.

Even if you're taking birth control pills, pregnancy can still happen due to missed doses, medications, or absorption issues. The key is knowing the signs, acting fast, and talking to your doctor. If you’re ever unsure, take a test and explore backup options to stay protected and informed.