What are the signs that Plan B didn't work?
If you’re worried about unintended pregnancy, you’re not alone. Nearly half of all pregnancies in the United States are unplanned.
Taking Plan B may be able to prevent an unplanned pregnancy after the heat of the moment has passed, though it’s not 100% effective.
If you took Plan B and you're wondering if it worked, you’re in the right place. Below, we outline how to know if Plan B failed and review some factors that can influence its efficacy.
How does Plan B work?
Nicknamed the “morning-after pill,” Plan B is a brand of emergency contraception that you can take within five days of having unprotected sex. You can purchase Plan B over-the-counter without a prescription.
Plan B works by delivering your body a strong dose of levonorgestrel, which is a synthetic form of progesterone. By administering 1.5 milligrams of levonorgestrel, Plan B may prevent pregnancy by delaying ovulation.
Ovulation occurs when a mature egg is released from your ovary into your fallopian tube. This egg waits there for 12 to 24 hours to be fertilized by sperm. If it’s not fertilized within this time frame, it will disintegrate. By delaying ovulation, Plan B can keep any sperm in your body from fertilizing your egg after unprotected sex.
Note: Plan B works by preventing pregnancy. It can’t end an existing pregnancy. As a result, it won’t work if a fertilized egg has already been successfully implanted in your uterus.
How to take Plan B
Plan B should be taken as soon as possible after unprotected sex, hence why it's referred to as an emergency contraceptive pill. But how long does Plan B stay in your system and when is it most effective? It’s most effective when taken within 72 hours, though it may still work for up to five days.
Once you take Plan B, you may experience some side effects, such as:
How do you know your Plan B didn't work?
Research shows that Plan B can be up to 89% effective, depending on when you take it. However, there’s always a chance that you may still get pregnant.
Here are a few potential signs that Plan B didn't work:
Missed period – The most tell-tale sign that Plan B didn’t work is if you don’t get your period within four weeks of taking the medication. While Plan B may cause your period to come earlier or later than expected, missing it altogether may indicate that you’re pregnant.
Spotting – Spotting is a common side effect of the Plan B emergency contraceptive pill, but you can also experience spotting from implantation. Implantation bleeding usually takes place 10 to 14 days after ovulation. In contrast, Plan B spotting typically sets in within a few hours or days of taking the medication.
Fatigue – While Plan B can cause fatigue, it usually only lasts a few days. Pregnancy fatigue, on the other hand, can persist through all three trimesters. Even the earliest stages of pregnancy can zap your energy.
Food cravings and aversions – Pregnancy can notably alter your food preferences. You may find yourself craving new foods or being put off by some of your favorite staples. You may also lose your appetite altogether. Food preference changes can set in within a few weeks of getting pregnant.
Heightened smell sensitivity – One reason why pregnancy can cause food aversions is the heightened sensitivity to smell. Women and people who menstruate often have much stronger responses to scents while they’re pregnant.
Morning sickness – If you find yourself feeling nauseous or vomiting for no reason, you may be pregnant. Unlike the name suggests, morning sickness can occur at any point in the day. Keep in mind that short-term nausea and vomiting are also potential side effects of Plan B.
Light-headedness and headaches – While Plan B can cause dizziness, so can the early stages of pregnancy. During pregnancy, your blood vessels dilate roughly 50% to funnel more blood flow to your developing fetus. Your blood pressure can drop as a result, leading to dizziness, lightheadedness, and headaches.
Needing to pee more often – While pregnant, your kidneys go into overdrive to filter your increased blood flow. As a result, you may find yourself taking more frequent trips to the bathroom. Increased urination typically begins right before your missed period.
Breast tenderness or swelling – As your hormones shift during pregnancy, your breasts may become sore, swollen, and tender. Your nipples and areolas may also darken and become enlarged. Breast tenderness is also a Plan B pill side effect, but nipple and areola changes are not.
Abdominal cramping – During pregnancy, more blood flows to the uterus, which can induce cramping and abdominal discomfort. However, cramping is also a common symptom of PMS and a side effect of Plan B.
Mood swings – As pregnancy alters your hormones, you may find yourself feeling more moody, irritable, sad, or anxious. You may also experience sudden mood fluctuations. That’s because pregnancy hormones can affect your brain’s neurotransmitters.
As you can see, cramping, food cravings, or bleeding after Plan B ingestion, are many of the early signs of pregnancy that resemble Plan B’s side effects. Thus, the only way to find out if you're pregnant is to take a pregnancy test.
What makes Plan B ineffective?
As we mentioned before, Plan B is not 100% effective. So, what influences its efficacy rate?
Here are a few factors that may affect how well Plan B works for you:
How quickly you take it – Plan B’s efficacy wanes as time goes on. If you take Plan B within three days, its efficacy rate can be as high as 75% to 89%. If you take it within four to five days, that rate may be lower.
Your menstrual cycle phase – Where you are within your menstrual cycle can also play a role in how well Plan B works. If you have unprotected sex while you’re ovulating or right after, Plan B may not work, since it won’t be able to delay ovulation.
Your weight – Plan B has been shown to be less effective for people who have BMIs of 30 or higher. If your BMI is between 30 and 35, you may want to take ella instead. It’s a prescription form of emergency contraction that may be more effective for people with higher BMIs.
Your medications – Certain medications and herbal supplements can interfere with Plan B, including:
Certain antibiotics and antifungal medications
St. John’s wort herbal supplements
If you’re taking any of these drugs, make sure to consult with your doctor before taking Plan B or any other emergency contraceptives.
Vomiting – If you throw up within two hours of taking Plan B, you may expel some of the medication in the process, leaving you unprotected.
Timing – It’s also important to note that Plan B won’t prevent pregnancy during sexual encounters that occur after you take it. If you plan to have sex after taking Plan B, make sure to use another form of protection.
What are the chances of pregnancy if Plan B didn't work?
Even if Plan B fails, you won’t necessarily get pregnant from one unprotected sexual encounter. It’s always possible, but it depends greatly on where you are in your menstrual cycle.
Research shows that the chances of a young, healthy couple getting pregnant from one instance of unprotected sex are around one in 20.
Your odds of getting pregnant will depend on your:
Why doesn't Plan B work during ovulation?
As we discussed earlier, Plan B’s primary method of preventing pregnancy is delaying ovulation. If you’ve already ovulated, there’s not much more Plan B can do.
Ovulation itself only lasts 12 to 14 hours, though you can still get pregnant for a few days before and after ovulation.
Is there anything else you can do during ovulation to prevent pregnancy?
Plan B is not your only safeguard against pregnancy. It's also not meant to be used as a regular birth control pill or method. So can you take Plan B on birth control? The short answer is, yes. In fact, it’s best used as a backup method when your primary birth control method doesn't go as planned.
Here are a few birth control methods that can work during any time of the month, including ovulation:
Favor: Get birth control and Plan B delivered to your door
As you can see, Plan B may be able to reduce your chances of getting pregnant after unprotected sex. If you need emergency contraception or a new birth control prescription, Favor has you covered.
At Favor, we make prescription birth control, emergency contraception, and skin care more accessible. One of our healthcare providers can recommend the best option for your reproductive needs, and Favor will ship it right to your home.
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Planned Parenthood. What’s the Plan B morning-after pill?
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Planned Parenthood. The Difference Between the Morning-After Pill and the Abortion Pill.
Mayo Clinic. Getting pregnant.
Plan B One Step. Possible Plan B side effects.
American Pregnancy Association. What is Implantation Bleeding?
American Pregnancy Association. Early Signs of Pregnancy.
NIH. Renal Physiology of Pregnancy.
American Pregnancy Association. Breast Changes During Pregnancy.
Planned Parenthood. Emergency Contraception.
Planned Parenthood. What’s the ella morning-after pill?
Cleveland Clinic. Morning-After Pill.
BBC. Sex: What are the chances?
Cleveland Clinic. Ovulation.
MedlinePlus. Birth Control.
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