Twenty-seven guides about emergency contraception, one question each. Timing and whether it worked, side effects and cycle changes, fertility worries, taking it alongside an IUD or an implant, where to buy it and what it costs, plus the legal and faith questions that sit outside the clinical ones. Start with the group that matches what you are trying to find out rather than reading from the top. Below the post list is the reference layer, built only from the FDA-approved product labels, the CDC 2024 contraception guidelines, ACOG and the World Health Organization, with the wording quoted rather than summarized: what the label says about an existing pregnancy, what changed in December 2022, and why no US authority publishes a weight cutoff in pounds.Contraception
Contraception
Every answer on this page has a document behind it, and the document is quoted
This is a topic where the internet repeats numbers nobody can trace. A weight cutoff in pounds. An effectiveness percentage. A claim about what the pill does to an existing pregnancy. Some of those are wrong, and the wrong ones travel further than the right ones.
These 27 guides answer the practical questions: timing, side effects, whether it worked, where to buy it, what it costs, and how it interacts with an IUD or an implant. Below the list is the reference layer, built only from the FDA-approved product labels, the CDC's 2024 contraception guidelines, ACOG and the World Health Organization, with the wording quoted rather than summarized.
For the timing math on a specific date, use the emergency contraception calculator. If you are deciding what to do right now, a pharmacist or a clinician can help immediately, and this page is not a substitute for either.
What each option is, how long you have, and what the numbers actually measure
| Method | Access | Window | Published outcome |
|---|---|---|---|
| Levonorgestrel 1.5 mg (Plan B and generics) | Over the counter, no prescription, no age restriction since 20 June 2013 | 72 hours on the label | The label states about 7 of every 8 women who would have become pregnant will not |
| Ulipristal acetate 30 mg (ella) | Prescription only | 120 hours | Observed pregnancy rate 2.2 percent at 48 to 120 hours, against an expected 5.5 percent |
| Copper IUD | Placed by a clinician | 5 days | Failure rate of 0.14 percent across 7,034 insertions in a 2012 review of 42 studies |
Two things about that table that get misread constantly
The levonorgestrel figure is not "87 percent of users avoid pregnancy," and it is not a per-act failure rate. It describes the share of expected pregnancies prevented, among the smaller group who would otherwise have conceived. The ulipristal figures only mean something as a pair: 2.2 percent observed against 5.5 percent expected. Publishing an observed rate without its expected rate makes the drug look either miraculous or useless depending on which half you drop.
The copper IUD figure has the same trap in reverse. The widely quoted 0.09 percent is a sensitivity analysis that excludes one outlier study. The headline figure across all 42 studies is 0.14 percent. WHO's own wording is that the copper IUD is more than 99 percent effective, which is the safest way to say it.
The window depends on which authority you are reading
The FDA label for levonorgestrel says 72 hours. CDC frames the emergency contraceptive pill window as 5 days. That is a real difference between labeled use and clinical guidance, not an error in either. CDC also notes that ulipristal and levonorgestrel perform similarly within 3 days, but that ulipristal has been observed to be more effective between 3 and 5 days.
On the copper IUD, CDC's wording is precise in a way secondary coverage usually drops: it may be placed within 5 days of the first act of unprotected intercourse. How Long Is Plan B Effective After Taking It? and Is Ella Better Than Plan B? work through choosing between them.
What the FDA-approved label says about pregnancy, and what changed in 2022
Several of the most searched questions in this collection are really one question: does this end a pregnancy. The approved label answers it directly, and the answer was made more explicit in December 2022.
Plan B One-Step will not work if a person is already pregnant, meaning it will not affect an existing pregnancy.
US Food and Drug Administration, Plan B One-Step drug safety information
On 23 December 2022 the FDA approved a labeling change that removed a sentence saying the product may prevent attachment of a fertilized egg to the uterus. The agency explained why in its own words.
FDA determined the current science supports a conclusion that Plan B One-Step works by inhibiting or delaying ovulation and the midcycle hormonal changes. The evidence also supports the conclusion that there is no direct effect on fertilization or implantation.
US Food and Drug Administration, December 2022
The current consumer leaflet describes the mechanism plainly: the product works before release of an egg from the ovary, and as a result usually stops or delays that release. The Drug Facts panel carries the instruction not to use it if you are already pregnant, on the stated grounds that it will not work.
A caution if you go looking for the label yourself. Two FDA-hosted documents are still online carrying the retired pre-2022 implantation wording, one revised in 2009 and one in early 2021. They are genuine FDA pages and they are out of date. Check the revision date on any label you find. Is Plan B Abortion? How the Morning-After Pill Actually Works goes through this carefully.
Ulipristal is not identical on this point, and should not be described as if it were
The ella label states that the likely primary mechanism is inhibition or delay of ovulation, and then adds that alterations to the endometrium which may affect implantation may also contribute to efficacy. It separately states that ella is not indicated for termination of an existing pregnancy. Levonorgestrel and ulipristal have different label language here, and collapsing them into one summary overstates the case for one and understates it for the other.
Neither is mifepristone
Mifepristone is approved to end an intrauterine pregnancy through ten weeks gestation, is used in a regimen with misoprostol, and must be prescribed by a provider certified under a restricted distribution program. Levonorgestrel emergency contraception is approved to reduce the chance of pregnancy after unprotected sex, is sold over the counter, and its label says it will not affect an existing pregnancy. They are different drugs with different approved uses. Can Plan B Cause a Miscarriage? covers the question this usually sits behind.
There is no weight cutoff in pounds. There is a BMI signal, and it is published.
The claim that emergency contraception stops working above 165 pounds, or above a BMI of 26, appears on a large share of the pages covering this topic. No US authority publishes either number. They trace back to a European labeling episode around 2013 and 2014 and were never adopted by the FDA, the CDC, ACOG or WHO.
What is published is narrower and more useful. The CDC's 2024 guidance states the position in one sentence.
ECPs might be less effective among persons with BMI greater than or equal to 30 kg/m2 than among persons with BMI less than 25 kg/m2.
CDC, US Medical Eligibility Criteria for Contraceptive Use, 2024
CDC classifies emergency contraceptive pills at BMI 30 or above as Category 2, meaning the advantages generally outweigh the theoretical or proven risks. The copper IUD is Category 1, no restriction at any BMI. CDC also notes that the levonorgestrel formulation might be less effective than ulipristal in women with obesity. There is no safety concern in any of this; the issue is effectiveness.
The FDA has published data on the point, though not on the levonorgestrel label. The approved label for ella carries a pooled analysis covering both drugs at BMI above 30.
| Drug | Observed rate | Expected rate | What the label says |
|---|---|---|---|
| Ulipristal acetate | 3.1% | 4.5% | Not significantly reduced compared with the expected rate |
| Levonorgestrel | 7.4% | 4.4% | Observed rate higher than the expected rate |
Read the second row carefully. At BMI above 30, the observed pregnancy rate on levonorgestrel was higher than the rate expected with no contraception at all. That is a subgroup analysis with wide, overlapping confidence intervals rather than a powered comparison, so it should not be read as proof that the pill makes pregnancy more likely. It is, however, the strongest published signal that levonorgestrel is a weaker choice at higher BMI, and it comes from an FDA-approved label rather than a blog.
What the authorities do not do is give you a number in pounds. There is no weight at which the FDA says the pill stops working, and the FDA has never added a weight limitation or warning to the levonorgestrel label. ACOG's public guidance notes that some research suggests reduced effectiveness with higher weight, and that copper IUDs are not affected by weight, without publishing a threshold. If BMI is a concern, the sourced answer is that the copper IUD carries no such limitation and ulipristal holds up better than levonorgestrel.
Five things repeated everywhere with no authority behind them
- "Plan B is 89 percent effective." The current FDA label says about 7 of every 8 women who would have become pregnant will not, which is roughly 87.5 percent, and it frames that as expected pregnancies prevented. The specific 89 percent figure comes from older trial reporting and appears on no current label or CDC, ACOG or WHO page.
- "It stops working over 165 pounds," or "over a BMI of 26." No FDA, CDC, ACOG or WHO source publishes a weight cutoff in pounds or kilograms, or a BMI 26 threshold. The only published comparison point is CDC's BMI 30 against BMI under 25.
- "Plan B works for up to 5 days." Three different windows get merged into one sentence here. The levonorgestrel label says 72 hours. CDC frames the pill window as 5 days. Ulipristal is labeled for 120 hours. None of those is a claim about what the levonorgestrel label says.
- "The copper IUD is 99.9 percent effective." Neither the FDA nor the CDC publishes that decimal. WHO says more than 99 percent effective. The peer-reviewed failure rate is 0.14 percent across all studies, or 0.09 percent in a sensitivity analysis excluding one outlier.
- "There is a limit to how many times you can use it." The CDC's 2024 Selected Practice Recommendations contain no recommendation on repeat use of emergency contraceptive pills at all. That is an absence of guidance, not a hidden restriction. Can Taking Plan B Too Many Times Make You Infertile? handles the underlying worry.
One claim that is well supported, from two authorities
Drugs used for emergency contraception do not harm future fertility. There is no delay in the return to fertility after taking ECPs.
World Health Organization, emergency contraception fact sheet
ACOG states the same thing: none of the emergency contraception methods have any effect on future fertility. The FDA label is silent on the question, so this one is properly attributed to WHO and ACOG rather than to the label. Can Plan B Make You Infertile? What the Science Actually Says is the guide for it.
Two practical points from CDC worth knowing
CDC advises taking a pregnancy test if there is no withdrawal bleed within three weeks, which is the sourced answer to the timing question in When to Take a Pregnancy Test After Plan B. On resuming regular contraception, CDC distinguishes the two pills: after ulipristal, wait at least 5 days before starting or resuming hormonal contraception; after levonorgestrel or combined pills, any regular method may be started immediately. Either way, CDC advises abstaining or using barrier methods for 7 days, or until the next period, whichever comes first.
All 27 guides, grouped by what you are trying to find out
The archive above runs newest first. These groups follow the order the questions usually arrive in. Timing math hands off to the emergency contraception calculator, and the rest of the health tools are in the health calculators collection.
What it is and how it works
Five guides on the mechanism, the timing and the difference between the two pills.
- Is Plan B Abortion? How the Morning-After Pill Actually Works The label language quoted above, worked through in full.
- Is Plan B the Same as Birth Control? Emergency use against ongoing contraception, and why the dose differs.
- How Long Is Plan B Effective After Taking It? The 72 hour label window, and why sooner is better within it.
- Does Plan B Work If You Already Ovulated? The mechanism question that decides whether the pill can help at all.
- Is Ella Better Than Plan B? Two different drugs with different windows, labels and BMI performance.
Timing, and whether it worked
Four guides for the days after.
- Should I Take Plan B If He Didn't Finish? The risk question people are usually too embarrassed to ask a pharmacist.
- How Do You Know If Plan B Failed? What a late period does and does not tell you.
- When to Take a Pregnancy Test After Plan B CDC advises testing if there is no withdrawal bleed within three weeks.
- Can Plan B Cause a Miscarriage? Separating Facts From Fear The label says it will not affect an existing pregnancy. This explains why.
Side effects and your body
Eight guides on what happens afterward, from the common to the rumored.
- What Are the Side Effects of Plan B? The listed effects, how long they last, and what is not on the list.
- How Long Does Plan B Spotting and Bleeding Last? Bleeding that is not a period, and when it stops being normal.
- Can a Plan B Mess Up Your Cycle? Early, late or heavier, and how long the disruption typically runs.
- Does Plan B Mess With Your Hormones? One dose against a monthly regimen, and what that actually does.
- Can Plan B Cause Weight Gain or Bloating? Fluid retention against fat gain, which are not the same thing.
- Does Plan B Make Your Boobs Bigger or Sore? Breast tenderness is listed. Size change is a separate claim.
- Can Plan B Cause a Yeast Infection or BV? Whether a hormonal shift can change vaginal flora, and what else might.
- How Long Does Plan B Stay in Your System? Half life against duration of effect, which people conflate.
Fertility worries
Two guides on the fear that comes up most often, answered from WHO and ACOG.
- Can Plan B Make You Infertile? What the Science Actually Says No effect on future fertility, and no delay in its return.
- Can Taking Plan B Too Many Times Make You Infertile? Repeat use, and the absence of any published limit.
Taking it alongside other things
Three guides on interactions and dosing.
- Can You Drink After Taking Plan B? Absorption, vomiting and the practical answer.
- Can You Take Plan B With an IUD or Nexplanon? Whether emergency contraception adds anything on top of a device.
- What Happens If You Take Too Much Plan B? Double dosing, repeat dosing, and what the label covers.
Getting hold of it
Three guides on buying, paying and storage.
- Do Gas Stations Sell Plan B? Where to Buy Over the counter since 2013, with no prescription and no age restriction.
- Is Plan B FSA Eligible? Paying for it with a flexible spending or health savings account.
- Does Expired Plan B Work? Shelf life, storage and what an expiry date means for potency.
Law and belief
Two guides that sit outside the clinical questions.
- Is Plan B Legal in Georgia, Texas, and Every Other State? State by state, and the distinction from medication abortion law.
- Is Plan B Haram or a Sin? A Respectful Look at the Faith Question How different traditions approach it, presented without taking a side.
Frequently asked questions
Does Plan B end an existing pregnancy?
No. The FDA states that Plan B One-Step will not work if a person is already pregnant, meaning it will not affect an existing pregnancy. In December 2022 the FDA removed label language about preventing implantation, saying the evidence supports no direct effect on fertilization or implantation.
Is emergency contraception the same as the abortion pill?
No. Mifepristone is approved to end an intrauterine pregnancy through ten weeks and requires a certified prescriber. Levonorgestrel emergency contraception is approved to reduce the chance of pregnancy after unprotected sex and is sold over the counter.
Is there a weight limit for Plan B?
No US authority publishes a cutoff in pounds. The CDC states that emergency contraceptive pills might be less effective at a BMI of 30 or above than below 25, and classifies them Category 2 there. The copper IUD is Category 1 at any BMI.
How effective is Plan B?
The label states that about 7 of every 8 women who would have become pregnant will not. That describes the share of expected pregnancies prevented, not the share of all users who avoid pregnancy, and it is not a per-act failure rate.
How long do I have to take emergency contraception?
The levonorgestrel label says within 72 hours. Ulipristal is labeled for up to 120 hours. The CDC frames the pill window as 5 days, and says a copper IUD may be placed within 5 days of the first act of unprotected intercourse.
Does Plan B affect future fertility?
The World Health Organization states that drugs used for emergency contraception do not harm future fertility and that there is no delay in the return to fertility. ACOG states that none of the emergency contraception methods affect future fertility.
Every quotation and figure on this page
- Levonorgestrel label and the 2022 change. FDA, Plan B One-Step drug safety information, for the mechanism wording, the existing pregnancy statement, the December 2022 determination and the 20 June 2013 nonprescription approval. Current labels are on DailyMed.
- Ulipristal label. FDA-approved prescribing information for ella, revised June 2021, for the mechanism, the 120 hour window, the observed and expected pregnancy rates and the pooled BMI analysis.
- CDC guidance. US Medical Eligibility Criteria for Contraceptive Use, 2024, MMWR Recommendations and Reports, and the US Selected Practice Recommendations for Contraceptive Use, 2024, published 8 August 2024, for the BMI categories, the copper IUD window and the guidance on resuming contraception.
- WHO. Emergency contraception fact sheet, for the fertility statement and the copper IUD effectiveness wording.
- ACOG. The top questions asked about emergency contraception, for the weight and future fertility statements.
- Copper IUD failure rate. Cleland K, Zhu H, Goldstuck N, Cheng L, Trussell J, Human Reproduction 2012, a review of 42 studies and 7,034 insertions, structured abstract hosted by the National Library of Medicine.
- Mifepristone. FDA information on mifepristone, for the approved indication and the prescriber requirement.
Where to go next
For timing against a specific date, use the emergency contraception calculator. Other health tools are in the health calculators collection, and everything else on the site is on the Waldev homepage.
This page is health information, not medical advice. It reports what the FDA-approved labels, the CDC's 2024 contraception guidelines, ACOG and WHO say as of August 2026. It cannot account for your medical history, your medications, your cycle or your circumstances, and it is not a diagnosis or a treatment plan.
Emergency contraception is time sensitive. If you are deciding whether to use it, a pharmacist can help immediately and without an appointment, and a clinician can discuss the copper IUD, which is the only option here with no BMI limitation. If you have severe abdominal pain in the weeks after taking it, or heavy bleeding, or you think you may be pregnant, contact a healthcare provider rather than waiting.
If the situation involved assault or coercion, a clinician or a local sexual assault service can help with more than contraception, including care that is time sensitive in the same way.