Illustration by Marta Pucci
What are the signs Plan B didn’t work? Emergency contraception explained.
How to know if Plan B was effective
Top things to know about emergency contraception:
Emergency contraception reduces the risk of pregnancy after sex.
About 1 in 4 women have used emergency contraception.
The copper IUD, hormonal IUD, and the morning-after pill are all effective at preventing pregnancy in emergencies.
You can know for sure that emergency contraception has worked when you get your next period, which could be delayed by up to seven days.
You can use emergency contraception as often as needed, but using a regular form of birth control is likely to be better for most people, with fewer unwanted side effects like nausea, headache, and abdominal pain.
Planned Parenthood offers an online tool that will help you learn more about your specific emergency contraception options.
What is emergency contraception?
Emergency contraception is a type of birth control. It reduces the risk of pregnancy after unprotected sex (1). It shouldn’t be used as regular birth control because it has a lot more side effects than other forms of birth control (1).
You may consider emergency contraception if you had unprotected sex and don’t want to become pregnant (1). You can take it on any day of the menstrual cycle. It’s safe to take 21 days after giving birth (1). It’s also safe to take five days after miscarriage, abortion, or ectopic pregnancy (1). You can take it if you’ve been using hormonal birth control but haven’t used it as directed, and you are worried you could become pregnant (1).
The three types of emergency contraception most commonly used are: emergency contraceptive pills, the hormonal intrauterine device (IUD), and the copper IUD (2). In this article, we will be talking about the emergency contraceptive pill, also known as the “morning-after pill”.
How does emergency contraception work?
Emergency contraception is taken to prevent pregnancy. For a pregnancy to occur, two sexual partners must have penis-in-vagina sex (3). One partner must produce sperm and the other must produce eggs (3). If one partner ovulates within five days of unprotected sex, pregnancy could happen (3). This is because sperm can live for about five days after sex (3). After the sperm and egg unite (fertilization) they are called a zygote (4). The zygote must implant into the lining of the uterus for a pregnancy to occur (4).
Emergency contraception works by either preventing the uniting of sperm and egg, preventing implantation into the uterine lining, or both (1).
Progestin emergency contraception pill (Levonorgestrel or Plan B)
Progestin emergency contraception is available over-the-counter in the USA, UK, and Canada.
In the USA, the progestin-only emergency contraception pill (usually known as Plan B) can be purchased in pharmacies by anyone of any age, without a prescription (2). You should take it as soon as you can after unprotected sex, but it’s most effective if taken within three days (2). You can take it for up to five days after sex (2). If you take it between three and five days, it might not be as effective, but is still worth taking (2). It works by delaying the release of the egg from the ovary (ovulation), which prevents the sperm from fertilizing it ( 5).
Antiprogestin emergency contraception pill (Ulipristal acetate or Ella)
Antiprogestin emergency contraception is available over-the-counter in the UK, and by prescription in the USA and Canada.
Antiprogestin emergency contraception pills (one of the available “morning-after” pills) are the most effective form of emergency contraceptive pill and available only by prescription in the USA (2, 6). This pill should be taken as soon as possible after unprotected sex, but you can take it up to five days later (2, 6).
This emergency contraception pill changes the way progesterone works in your body (2, 6). It works by preventing or slowing ovulation (2, 6). When ovulation is postponed or halted, there is no egg for sperm to fertilize, and pregnancy is prevented (2).
What are the signs that Plan B has failed?
If you used emergency contraception like Plan B, it’s likely that you want to know as soon as possible if it was effective. Unfortunately, the answer doesn’t come overnight. You’ll have to wait until your period arrives to know for sure.
What if my menstrual period doesn’t arrive?
If you don’t get your period when you are expecting it, or it’s more than seven days late, it’s likely that Plan B didn’t work for you (5). You could experience spotting or bleeding after you take Plan B and your period should arrive within seven days of when it’s expected in your next menstrual cycle (5).
The importance of tracking your cycle
Tracking your menstrual cycle and its related experiences with Clue can help you get to know your body. During the menstrual cycle, lots of hormonal changes happen and when you track the experiences that go along with them, you can begin to link them together. You might begin to recognize signs that you will ovulate soon or become aware of how you usually feel in the days before your period.
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What are the early pregnancy symptoms?
If you took the morning-after pill, your period could be up to a week later than usual (5,6). If this happens, know it’s a common side effect (5,6). If it’s been more than three weeks and you still haven’t gotten your period, take a pregnancy test (5,6). You can also look for other changes in how your body is feeling.
Here are some possible early signs of pregnancy (7,8):
Missed period
Feeling very tired
Headache
Feeling lightheaded or faint
Food aversions or cravings
Sensitivities to smells
Swollen or tender breasts
Pelvic, back, or leg pain
Bloating
Nausea/vomiting
Needing to pee often
Constipation
Mood swings
What if I get a positive pregnancy test?
It can be hard to wait, but the only way to know if emergency contraception worked for you is to see if your period comes when you expect it. If you took the morning-after pill, it could be up to a week late. If you do not experience a period within one week of its expected date, take a pregnancy test. If you get a positive pregnancy test, it is likely that the emergency contraceptive did not work and conception occurred. If it is an unwanted pregnancy, visit a healthcare provider, like Planned Parenthood in the USA, to learn more about your options. Note that many “crisis pregnancy centers” in the USA offering free pregnancy testing and ultrasounds are not real medical clinics. They are designed to talk people out of abortion and don’t have to follow guidelines to keep your health information private (9). They are usually religious nonprofit organizations with the primary aim of keeping people from having an abortion (9).
What can I do if my emergency contraception didn’t work?
If you are pregnant, know that emergency contraceptive pills won't harm the pregnancy or the fetus (2). If you are pregnant, there are three options: pregnancy with parenting, pregnancy with adoption, and abortion (10). If you choose abortion, the state or country you live in, and how far along you are, may limit your options because some states and countries ban abortion or control who can access it and when (10).
How effective are emergency contraceptives?
It’s hard to study the effectiveness of the morning-after pill because it can be difficult to know when people are ovulating and when they had sex (11). Based on the data scientists have, one-dose emergency contraception pills are effective at preventing pregnancy between 50-100% of the time (12). The range is so wide because people don’t get pregnant every single time they have unprotected sex, and there are lots of different factors that lead to conception.
What causes Plan B to fail?
Emergency contraception can be effective at preventing pregnancy, but sometimes people take it and still become pregnant. Here are the three main reasons why this happens:
1. Ovulation happened before you took the pill
Emergency birth control is all about timing. It's recommended that you take the pill as soon as you can after unprotected sex—if you wait too long, you might miss the window during which the pill can be effective.
If you take it right after sex, it can prevent you from ovulating if you haven’t started already (2). If you have sex during or after ovulation, your emergency contraception pill won’t be effective (13).
If you have unprotected sex again after you take the pill in the same cycle, it might not work (13). Use a barrier method, like a condom, if you have sex and want to prevent pregnancy.
2. The morning-after pill is more effective for some body types
Healthcare providers use the Body Mass Index (BMI) scale to group people into generic categories based on height and weight (14). BMI doesn’t consider a person’s age, sex assigned at birth, muscle mass, or other health factors like food intake and exercise. It also doesn’t differentiate between lean body mass and fat mass, which means people like athletes with low body fat can have a high BMI (15).
Remember that while BMI is often used as a screening tool, a higher BMI doesn’t mean someone is unhealthy.
Current studies suggest that Plan B is less effective for people who have a BMI of 30 or higher (13). This is because fat tissue can impact levels of reproductive hormones and the studies that look at the efficacy of birth control weren’t done on women with a higher BMI (16).
People who have a BMI of 30 or higher who take levonorgestrel (Plan B) emergency contraception might become pregnant more frequently than those with a BMI of 25 or less (13, 17). This doesn’t mean that if your BMI is 30 or higher, you shouldn’t take emergency contraception.
If you have a BMI of 25 or higher, you might want to call your healthcare provider for a prescription for the antiprogestin emergency contraceptive pill (13). It might offer better prevention of pregnancy for your body type (13). If you have a BMI of 30 or higher, you might want to discuss options with your healthcare provider, including an IUD for emergency contraception (2,13).
If you are considering an IUD (copper or hormonal) as emergency birth control, a healthcare provider must insert it within 5 days after you have unprotected sex (2). You should call your healthcare provider as soon as you realize you need emergency contraception. It can be difficult to get an appointment for an IUD insertion on short notice, so get in contact as quickly as possible. If you do not have access to a healthcare provider, taking an over-the-counter progestin emergency contraceptive pill is better than taking nothing.
3. You’re taking a medication that interacts with emergency contraception
Some drugs and herbal products can cause emergency birth control pills to be less effective (6, 18). See the table below.
Be sure to double check the emergency contraceptive package information for more detailed information. You should not stop taking any prescription medication without first consulting your healthcare provider. Doing so can cause severe side effects. Hormonal birth control can also cause interactions with the antiprogestin emergency contraceptive pill.
Now you know more about emergency contraception
It is a good idea to stock up on an emergency contraceptive pill in case you need one in the future. You can ask your healthcare provider for a "just-in-case" prescription or grab an over-the-counter pill from the pharmacy to keep at home (just be mindful of the expiration date). You can track every time you use contraception, including the morning-after pill, in the Clue app.
Don't forget—the emergency contraceptive pill, like hormonal birth control, does not prevent sexually transmitted infections (STIs). If you think you might be at risk for STIs, always use a barrier method, like a condom, during sex and talk to your healthcare provider about getting an STI screening.
FAQs
How does Plan B work?
The emergency contraceptive pill (ECP) Plan B works by blocking or delaying ovulation (18). They change the body’s hormones to stop an egg from being released (18). If there is no ovulation, then there is no egg to be fertilized by sperm (19). An egg can only be fertilized by sperm for about 12–24 hours after ovulation (2). Sperm can lead to a pregnancy for up to five days after it enters the body (2). It’s in this part of the fertile window, before you ovulate, that ECPs can be most effective, or perhaps effective at all (19).
Does Plan B work during ovulation?
The effectiveness of ECPs depends on when you take them. If you take a pill in time to prevent ovulation, it is more effective (19). If you have unprotected sex a few days before ovulation and take an ECP, you’re less likely to get pregnant than if you had sex one day before ovulation (19). This is why ECPs should be taken as quickly as possible after unprotected sex. If you take an ECP too close to ovulation, it may not work (20).
Does bleeding after Plan B mean it worked?
After taking Plan B, your vaginal bleeding might be different than it was in previous cycles (20). You might experience bleeding or spotting before your period, but the only way to know Plan B worked for sure is to take a pregnancy test if you don’t get your period within seven days of when you expected it (20).
How many times can I take Plan B?
Plan B emergency contraception was not designed to be used as a daily birth control (20). Using it this way would be more expensive and cause more side effects than birth control. If you used Plan B and you need to use it again, it will work the same way each time you take it (20). You cannot build up a tolerance to Plan B. Plan B does not become less effective over time (20). The Ella emergency contraceptive pill has not been studied for more than one use in a cycle (6).
