Morning-after pills are good at stopping an egg from being released, but they do little once that release is underway or finished. So whether a pill works depends less on how fast you take it than on where you are in your cycle. A copper IUD placed within 5 days of sex is different: it doesn’t depend on ovulation timing at all.1PubMed. Copper T380 intrauterine device for emergency contraception: highly effective at any time in the menstrual cycle Since most people can’t pinpoint their ovulation day, taking a pill anyway still makes sense.
How the Morning-After Pill Actually Prevents Pregnancy
Each month your brain releases a burst of a hormone, called an LH surge, that triggers an egg to leave the ovary about a day later. Plan B, made of levonorgestrel, works by holding back that surge.2Nurx. Nurxâ„¢ Healthcare from Home ella, made of ulipristal acetate, can delay the surge or push back its peak if it has just started, and it may also directly stop the egg’s release.3PubMed. Ulipristal acetate: a review of its use in emergency contraception
Delay works because pregnancy needs sperm and egg together at the same time. Sperm can survive in the body for up to about 5 days, so sex in the days before ovulation can cause pregnancy. If a pill pushes ovulation later than the sperm can survive, the timing breaks and the sperm die before an egg arrives. That is why a pill taken days after sex can still help.
When a pill is taken early enough, ovulation is pushed back by days, not cancelled, so the egg is still released later in that same cycle. The pill is a one-time fix for one act of sex, not ongoing protection for later sex in the same cycle.
The pill does not work by other routes. At normal doses, levonorgestrel does not damage sperm.4PubMed Central. Does levonorgestrel emergency contraceptive have a post-fertilization effect? A review of its mechanism of action Nine of ten studies found Plan B does not change the uterus lining’s readiness for a pregnancy.5PubMed. Effect of levonorgestrel emergency contraception on implantation and fertility: A review That means it is not an abortion pill and cannot end a pregnancy that has implanted.
What Happens If You Take It Near or After Ovulation
Among women who took Plan B on ovulation day or later, pregnancies happened at the same rate as with no pill at all.6PubMed. Contraceptive efficacy of emergency contraception with levonorgestrel given before or after ovulation In another group taking it 1 to 2 days after ovulation, pregnancies matched what was expected without it.7PubMed. Effectiveness of levonorgestrel emergency contraception given before or ovulation–a pilot study
ella delays ovulation less and less as ovulation approaches.8PubMed. Ulipristal acetate: critical review about endometrial and ovulatory effects in emergency contraception One to two days before ovulation, at the peak of the LH surge, it acts like a dummy pill.9PubMed. Ulipristal acetate: critical review about endometrial and ovulatory effects in emergency contraception Still, ella works a little later into the fertile window than Plan B, because it can act after the LH surge has begun.10PubMed. Ulipristal acetate: a review of its use in emergency contraception
The days just before ovulation are a gray zone. The surge starts roughly a day or more before the egg is released, so there is a stretch when the signal has begun but the egg is still in the ovary. Plan B needs to act before the surge starts, so as the surge gets underway it has less and less left to hold back. The closer you think you are to ovulation, the less any pill can be counted on, and the decline is gradual, not a sharp cutoff.
A few researchers argue that ella’s steady effectiveness must come from changes to the uterus lining.11PubMed. UPA and LNG in emergency contraception: the information by EMA and the scientific evidences indicate a prevalent anti-implantation effect But studies looking directly at pregnancy rates after ovulation found no extra protection.12PubMed. Does ulipristal acetate emergency contraception (ella®) interfere with implantation? So you shouldn’t count on either pill if you know you’ve already ovulated.
If you’re near ovulation and choosing between the two, ella covers more of the days just before ovulation. It needs a prescription in the US, while Plan B doesn’t. If you can’t reach ella quickly, take Plan B rather than wait.
If you think you are at or past ovulation, taking a pill is still reasonable, because you rarely know for sure that ovulation has happened and the pill costs little. Treat it as possibly doing nothing, and don’t make it your only plan. Look into a copper IUD the same day, since it works whether or not the egg has been released. If you can’t get one, take a pregnancy test when it’s due.
The Option That Works Even If You’ve Ovulated
A copper IUD, a small T-shaped device placed in the uterus, is the most effective emergency contraception.13PubMed. Emergency Contraception In over 1,700 women, none became pregnant in the first month after copper IUD placement, including those past ovulation.14PubMed. Copper T380 intrauterine device for emergency contraception: highly effective at any time in the menstrual cycle So it works at almost any point in the cycle, as long as a pregnancy test is negative first.15PubMed. Copper T380 intrauterine device for emergency contraception: highly effective at any time in the menstrual cycle It also works regardless of weight.16PubMed Central. Practical Advice for Emergency IUD Contraception in Young Women Afterward, it can stay in for up to 10 years as hormone-free birth control.17PubMed. Emergency Contraception
A hormonal IUD worked about as well: one pregnancy in 317 women versus none in 321 with copper.18Eunice Kennedy Shriver National Institute of Child Health and Human Development. Science Update: Hormonal IUD as effective as a copper IUD at emergency contraception and with less discomfort, NICHD-funded study suggests Side effects like cramping or bleeding affected about 5 in 100 with either type.19Eunice Kennedy Shriver National Institute of Child Health and Human Development. Science Update: Hormonal IUD as effective as a copper IUD at emergency contraception and with less discomfort, NICHD-funded study suggests
Copper makes the environment hostile to sperm, so they are impaired before they can reach and fertilize an egg. That mechanism is also why it is not an abortion method: it is placed to stop fertilization, and it is not meant for someone already known to be pregnant.
To get one in time, call a clinic or Planned Parenthood and say it’s for emergency contraception. Ask for an appointment within 5 days of sex, and expect a urine pregnancy test before placement. You can still take a pill now while you wait for the appointment.
Placement takes a few minutes in an exam room. Cramping during and after is common, and spotting for days afterward is normal. The tradeoff is access: an IUD needs a clinic visit within the window, while a pill can be taken from a pharmacy shelf in minutes.
How to Tell Whether You’re Ovulating
Only 15% of women had an exact 28-day cycle, though 34% believed they did.20PubMed. Can apps and calendar methods predict ovulation with accuracy? Even in 28-day cycles, ovulation most often fell on day 16, not day 14.21PubMed. Can apps and calendar methods predict ovulation with accuracy? Period apps predicted the right ovulation day no more than about 21% of the time.22PubMed. Can apps and calendar methods predict ovulation with accuracy? So an app saying you’re “fertile” or “not fertile” isn’t enough to decide whether to take a pill. Take the pill as soon as possible rather than trying to calculate.
Ovulation can shift from cycle to cycle because of stress, illness, travel or sleep changes. Apps mostly estimate from your past period dates, so they predict ovulation but don’t detect it.
Some signs hint that ovulation may be near. Clear, stretchy vaginal discharge often appears before ovulation. A positive home ovulation test means the LH surge has started, and after one, ella is more likely to help than Plan B, and an IUD most of all.
These urine strips detect the surge, so a positive one means ovulation is likely within about a day or two, not that it has already happened. A negative strip on the day of sex doesn’t prove you’re safe: the surge may have come earlier or not yet, or the test may have been done at the wrong time. Most people don’t have strips on hand after unprotected sex, so they help only if you happened to be testing already.
Timing, Weight and Medicines That Lower Effectiveness
Pills taken within 3 days led to about 0.8% pregnancies versus 1.8% when taken on days 3 to 5.23PubMed. Effectiveness of emergency contraceptive pills between 72 and 120 hours after unprotected sexual intercourse Keeping a pill at home helps you start sooner.24PubMed. The effects of advance provision of emergency contraception on adolescent women’s sexual and contraceptive behaviors
Taking it the same day is better than waiting until the next morning, even though the label allows up to 3 or 5 days.
Body weight matters too. Plan B failed about four times more often in women with obesity than in normal-weight women.25PubMed Central. Safety and effectiveness data for emergency contraceptive pills among women with obesity: a systematic review Above about 80 kg (176 lb), pregnancy rates with Plan B rose to the level expected without it.26PubMed Central. Safety and effectiveness data for emergency contraceptive pills among women with obesity: a systematic review Under 75 kg (165 lb), pregnancy rates were under 2%.27PubMed Central. Safety and effectiveness data for emergency contraceptive pills among women with obesity: a systematic review
These findings describe a trend, not a cutoff where the pill suddenly stops. If you weigh more, ella or an IUD is a better choice, though taking Plan B is better than nothing if it’s all you can get fast.
Some medicines also weaken Plan B. Some seizure medicines, tuberculosis drugs like rifampicin, some HIV drugs, and St John’s wort speed up how the liver clears it.28StillSafe Philippines. What Medicines Can Make Plan B Less Effective? Drug Interactions You Should Know Griseofulvin, an antifungal, is on the same list.29Leeds, Grenville and Lanark District Health Unit. Emergency Contraceptive Pill (Plan B) Plan B and ella shouldn’t be taken together, since one weakens the other.30Leeds, Grenville and Lanark District Health Unit. Emergency Contraceptive Pill (Plan B)
The effect can last for a while after stopping such a medicine, so mention anything taken recently. Over-the-counter supplements count, and St John’s wort is an example people often forget to mention.
Tell the pharmacist every medicine and supplement you take, and ask whether a double dose or an IUD is advised.
Your Period Afterward and When to Take a Pregnancy Test
Taken in the first 3 weeks of the cycle, Plan B tends to make that cycle shorter, more so the earlier it’s taken.31PubMed. Bleeding patterns after use of levonorgestrel emergency contraceptive pills The next period may also last longer than usual.32PubMed. Bleeding patterns after use of levonorgestrel emergency contraceptive pills Bleeding between periods happens in only about 5 in 100.33PubMed. Bleeding patterns after use of levonorgestrel emergency contraceptive pills
Because the pill moves the timing of ovulation, the rest of the cycle shifts with it, so the next period can arrive on a different date than usual. A small change isn’t a sign that something went wrong, and this settles in the following cycle. Spotting a few days after the pill is not the same as a period, so count the next real period when timing a test.
If your period hasn’t come within 3 weeks of taking the pill, take a pregnancy test.34Planned Parenthood. Plan B Morning-After Pill | How Plan B Works & Side Effects If you track your cycle and your period is a week late, test then.35Twentyeight Health. Plan B and Your Period: What to Expect After Taking the Morning-After Pill Testing too early can give a false negative before the pregnancy hormone shows up.36Twentyeight Health. Plan B and Your Period: What to Expect After Taking the Morning-After Pill
A test taken in the first days after sex can’t detect a pregnancy yet, so wait for those timings. If a test taken at the right time is negative but your period still hasn’t come, repeat it a few days later. First-morning urine can make an early result more reliable, since it’s more concentrated. A positive result is reliable, and the next step is to contact a clinic.
When you start regular birth control afterward, remember you can still get pregnant later in the same cycle, since ovulation was only delayed. After ella, wait 6 days before starting hormonal birth control.37Planned Parenthood. Plan B Morning-After Pill | How Plan B Works & Side Effects Use condoms until the new method takes effect.
If It Doesn’t Work, Is the Pregnancy Harmed
Taking the morning-after pill while already pregnant won’t harm the pregnancy.38Planned Parenthood. Does the Morning After Pill Work If You Are Ovulating? If you take Plan B and still get pregnant, it isn’t expected to raise the chance of birth defects.39MotherToBaby. Levonorgestrel (Plan B One-Step®) ella taken after ovulation doesn’t increase miscarriage.40PubMed. Does ulipristal acetate emergency contraception (ella®) interfere with implantation?
Taking a pill just in case is safe when you’re unsure whether you’ve ovulated. Its only downside is that it may not help, and you may get mild nausea or a headache.
After a positive test, contact a doctor or clinic early to confirm the pregnancy. Ask for an early ultrasound if you have one-sided pain or bleeding. All options remain open, whatever you decide.