When Is Plan B Effective

When Is Plan B Effective

all comments made to this page
new replies to my comments

Note: an email address is necessary if you wish to receive notifications. If provided, it will not be published publicly.
Note: an email address is necessary if you wish to receive notifications. If provided, it will not be published publicly.
The majority of women have heard of Plan B. It’s often simply marketed as this thing that you take any time you’ve had unprotected sex or a contraceptive failure—that is, if you don’t want to become pregnant—but how effective is Plan B really? What is Plan B, and how does it work? Are there side effects? What are they? Fewer women know the answers to these questions. Luckily, to fully understand how effective Plan B is, you need to understand what Plan B is and how it works so you learn the answers to all these questions.
Chances are, if you’re looking up Plan B effectiveness, you get that it’s a pill that helps prevent pregnancy, but to be more accurate, Plan B is a large dose of levonorgestrel . Levonorgestrel is a progestin that can prevent pregnancy primarily by preventing ovulation, but it may also prevent implantation.
Progesterone is a hormone that’s always present during your menstrual cycle. It maintains your uterine lining after ovulation. If you become pregnant, progesterone keeps you from getting a period. Plan B essentially mimics pregnancy by delivering a large dose of progesterone (levonorgestrel mentioned above) so that the body already “thinks” it’s pregnant, doesn’t ovulate, and instead continues to thicken the uterine lining. As this large dose dissipates, withdrawal bleeding occurs, which usually resembles a period.
Plan B effectiveness hinges on when you take it. The manufacture may tout it prevents 7 out 8 pregnancies, but realistically that’s likely only with perfect timing. Yes, Plan B must be taken within 72 hours, but there’s more to that story.
If Plan B is taken early in your cycle, it probably does have the suggested upwards of 89% effectiveness, but closer to mid-cycle, probably not, and after ovulation? It’s nearly a pointless measure. This is because you can’t prevent ovulation if it’s already happened.
After ovulation, all Plan B does is work to thicken the uterine lining more to prevent implantation. The later in your cycle you take it, the less effective it becomes.
The reason it’s generally recommended to take Plan B any time you’ve had unprotected sex and don’t wish to become pregnant is that not all women know when they ovulate . Honestly, if they did, they wouldn’t need Plan B because they would know if the sexual act occurred during a fertile time.
Pregnancy is actually only possible about one week out of the month. You have the viability of sperm at about 5 days, and the lifespan of an egg at around 24 hours. You can read more about your chances of pregnancy here , but long story short, in general, sex just before or just after a period is very unlikely to result in pregnancy. Sex mid-cycle has the highest chance.
Sadly, not all women ovulate mid-cycle. You can’t just assume if the sex wasn’t mid-cycle you won’t become pregnant and don’t need Plan B. It is actually possible to become pregnant from sex just after your period (when Plan B would be most effective). At mid-cycle when you’re most likely to become pregnant, Plan B will at least hinder implantation by thickening the uterine lining and subsequently causing withdrawal bleeding to thin it.
The only situation where we would say you’re probably just suffering side effects for no reason by taking Plan B is when the sex occurred in the final week before your period. Why?
First, ovulation has likely already occurred by a long shot. There probably is no chance of pregnancy, to begin with. Second, there is very little time to thicken the uterine lining. Additionally, if you are basal body temping and know when you ovulate, there is no reason to take Plan B unless you’re in a fertile period.
Side effects of plan B are basically a ramped-up version of PMS but may also mimic pregnancy symptoms. These include nausea, fatigue, feeling hot, discharge changes, bloating, cramping, and gas. This is because, as stated back there on how Plan B works, you’re creating a hormonal situation akin to pregnancy.
However, the most common Plan B side effect is irregular bleeding. Enough so you can read an entire page on this topic here.
I hope this has helped answer your questions about how effective is Plan B, but if not, we welcome comments and questions here at Life with Gremlins.
Plan B, also known as the morning after pill, is an emergency contraceptive that if taken within 72 hours of an unprotected sexual act can help dramatically reduce the chance of pregnancy. However, chances are if you are searching about bleeding after taking Plan B you already know what it…
Let’s start out by getting this out of the way: no one can tell you whether you are or are not pregnant over the Internet. I can’t. A quiz can’t. Scrutinizing timing and symptoms can’t. The only way to confirm a pregnancy is in person via examination, urine, or blood…
While for most something like a missed period seems a pretty obvious reason to take a pregnancy test, there are cases out there where pregnancy symptoms are a more significant deciding factor. Maybe you don’t have regular menses. Maybe you’re concerned you may just be experiencing early pregnancy bleeding and…
Our site contains affiliate links, including the Amazon Services LLC Associates Program. These along with other advertising help make Life with Gremlins possible. You can learn more about this in our privacy disclosure . Thank you for your support!

All

Select the section you want to search in

All
Consumer
Professional
Pill ID
Interactions
News
FDA Alerts
Approvals
Pipeline
Clinical Trials
Care Notes
Natural Products

Browse all medications:

a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
0-9

Advanced Search

Medical Answers
How effective is Plan B and how late can you take it?

I accept the Terms and Privacy Policy

Select one or more newsletters to continue.

Ad Choices

We comply with the HONcode standard for trustworthy health information.

Copyright © 2000-2022 Drugs.com. All rights reserved.

Medically reviewed by Sally Chao, MD . Last updated on July 30, 2021.
Plan B ( levonorgestrel ) is estimated to be 60% to 94% effective at preventing pregnancy when taken within 3 days (72 hours) after unprotected sex. Somewhere between 0.6% to 2.6% of women who take Plan B within this time frame will still become pregnant.
While Plan B can be taken up to 72 hours after unprotected sex, its efficacy decreases with time, and it is best to take it as soon as possible. For example, the chances of pregnancy are higher if Plan B is taken 4 days after unprotected sex, but are subsequently lowered if taken 3 days, 2 days, 1 day or within 24 hours after unprotected sex. However, the American College of Obstetricians and Gynecologists notes that some studies suggest that it can be moderately effective at preventing pregnancy up to 5 days after unprotected sex. Five days after unprotected sex is the latest time with which Plan B has been shown to lower your chances of pregnancy.
The efficacy of Plan B is also affected by the time at which it is taken within your menstrual or reproductive cycle. Plan B works best when taken before ovulation, or when an ovary releases an egg. Once there is a surge in the hormone that initiates ovulation and ovulation begins, Plan B cannot prevent pregnancy. Its primary mechanism of action is to change hormone levels such that ovulation is delayed. This is why it is important to take Plan B as soon as possible after unprotected sex. As treatment is delayed, ovulation becomes more imminent (if it has not yet occurred).
A review of studies in Clinical Obstetrics and Gynecology showed that among 492 women who took Plan B after unprotected sex, those who took it on or after the day of ovulation had the same pregnancy rate as would be expected among women who used no contraception at all. By comparison, none of the women who took Plan B before ovulation became pregnant.
In the event of another unprotected sexual encounter after Plan B is taken, Plan B will not protect against pregnancy—you will need to take Plan B again after another unprotected sexual encounter.
Plan B may also be less effective at preventing pregnancy in women who are overweight or obese. Studies reviewed by Cochrane suggest that the dose of levonorgestrel in Plan B has a lowered potency when taken by women who have a higher body mass index.
The easiest way to lookup drug information, identify pills, check interactions and set up your own personal medication records. Available for Android and iOS devices.
Subscribe to Drugs.com newsletters for the latest medication news, new drug approvals, alerts and updates.
Drugs.com provides accurate and independent information on more than 24,000 prescription drugs, over-the-counter medicines and natural products. This material is provided for educational purposes only and is not intended for medical advice, diagnosis or treatment. Data sources include IBM Watson Micromedex (updated 5 July 2022), Cerner Multum™ (updated 27 June 2022), ASHP (updated 16 May 2022) and others.
Help support Drugs.com by allowing ads...

Angle down icon
An icon in the shape of an angle pointing down.

Angle down icon
An icon in the shape of an angle pointing down.

Angle down icon
An icon in the shape of an angle pointing down.

Angle down icon
An icon in the shape of an angle pointing down.

Angle down icon
An icon in the shape of an angle pointing down.

Angle down icon
An icon in the shape of an angle pointing down.

Angle down icon
An icon in the shape of an angle pointing down.

Angle down icon
An icon in the shape of an angle pointing down.

Angle down icon
An icon in the shape of an angle pointing down.

Angle down icon
An icon in the shape of an angle pointing down.

Home

Chevron icon
It indicates an expandable section or menu, or sometimes previous / next navigation options.

Health

By

Ashley Laderer

Twitter icon
A stylized bird with an open mouth, tweeting.

Twitter

Snapchat icon
A ghost.

Snapchat

Fliboard icon
A stylized letter F.

Flipboard

Pinterest icon
The letter "P" styled to look like a thumbtack pin.

Pinterest

Link icon
An image of a chain link. It symobilizes a website link url.

Copy Link

This article was medically reviewed by Lauren Demosthenes, MD, OB-GYN, senior medical director at Babyscripts .

Our stories are reviewed by medical professionals to ensure you get the most accurate and useful information about your health and wellness. For more information, visit our medical review board.

Ashley Laderer is a freelance writer from New York who specializes in health and wellness. Follow her on Twitter @ashladerer

INSIDER

Plan B: Side effects, how long they last, and how to get relief

HEALTH

7 important things to know before taking Plan B, according to OB-GYNs

HEALTH

4 unexpected health benefits of going on birth control

INSIDER

How does birth control work and which methods are most effective

Reference Library
Reproductive Health

Chevron icon
It indicates an expandable section or menu, or sometimes previous / next navigation options.

Close icon
Two crossed lines that form an 'X'. It indicates a way to close an interaction, or dismiss a notification.

Plan B has a 95% chance of preventing pregnancy if you take it within 24 hours. If you take it within 72 hours, your chances reduce to 89% .
Note: Plan B, sometimes referred to as the "morning-after pill," is an over-the-counter form of emergency contraception you can take to prevent pregnancy after having unprotected sex.
"Plan B is FDA approved for use up to 72 hours after unprotected sex. It can be used up to 120 hours after, but the further out from intercourse, the less effective it will become," Nicole M. Bender , MD, an OB-GYN at Keck School of Medicine of USC.
So, for max protection, take the pill as quickly as you can get it.
The active ingredient in Plan B that prevents pregnancy is a hormone called levonorgestrel, which is a synthetic version of progesterone.
Aileen Gariepy, MD , OB-GYN at Yale Medicine and associate professor at Yale School of Medicine says that levonorgestrel works to prevent pregnancy by:
Plan B won't work if a pregnancy has already been established, says Gariepy. The only way to know for sure if you're pregnant is to take a pregnancy test . However, you can also
Mcstories.
Crossdressers Cum Shots
Why Does My Vagina Smell Like Onions

When Is Plan B Effective

Report Page