Emergency Contraception: Which Option Works Best and When

Missed or broken condom, late or missed pill, or unprotected sex and you need backup quickly.

Quick answer: Emergency contraception (EC) prevents pregnancy after unprotected sex and comes in three options: the copper IUD, the prescription pill ulipristal acetate (ella), and over-the-counter levonorgestrel pills (Plan B and generics). The copper IUD is the most effective, then ella, then levonorgestrel; time since sex and body weight affect pill performance.

Get it checked if you have severe pain after IUD insertion, ongoing heavy bleeding after an EC pill, or symptoms of pregnancy despite taking EC.

What emergency contraception is and how it works

Emergency contraception is a short-term method used after unprotected sex to reduce the chance of pregnancy. It does not terminate an established pregnancy, and it works mainly by delaying or preventing ovulation, and in the case of the copper intrauterine device, by preventing fertilization and possibly preventing implantation.

Mechanisms in plain words. Levonorgestrel and ulipristal acetate are pills that act on the hormonal process that triggers ovulation. If ovulation has already happened and an egg is released, those pills are less likely to prevent pregnancy. The copper IUD creates a local environment in the uterus that is toxic to sperm and eggs, and it works even after ovulation, which is why it is the most effective option.

Evidence and limits. High-quality studies show that copper IUDs have pregnancy rates well under 1% when inserted within five days of unprotected sex or within five days of ovulation. Ulipristal acetate offers better efficacy than levonorgestrel when taken within its window, and levonorgestrel is less effective the later it is taken and in people with higher body weight. No EC pill will work if a pregnancy is already established.

Who this is for. EC is for anyone who had unprotected sex, experienced birth control failure, missed multiple pills, or was forced into sex. It is safe for most people, but options vary if you are breastfeeding, have certain medical conditions, or are taking medications that interact with EC pills.

Plan B how long after: levonorgestrel timing and rules

Plan B and its generics contain levonorgestrel, a progestin taken as a single high-dose pill. The official window is up to 72 hours after unprotected sex, though effectiveness is highest the sooner you take it. Try to take it as soon as possible because every 12-hour delay reduces its effectiveness.

How well it works. When taken within 24 hours, levonorgestrel reduces the risk of pregnancy by most estimates by 60 to 85 percent compared with no EC, but that protection drops closer to the 72-hour mark. Exact numbers vary between studies, which is why earlier is better.

Who should not rely on it. Levonorgestrel is less reliable in people with higher body weight or body mass index (BMI). Some guidance suggests reduced effectiveness in people over about 155–176 pounds, but studies give a range and are not unanimous. If your weight or BMI is a concern, consider ella or the copper IUD instead.

Interactions and breastfeeding. Levonorgestrel is considered safe during breastfeeding; however, if you are taking enzyme-inducing drugs for epilepsy, tuberculosis, or certain herbal supplements like St. John’s wort, levonorgestrel may be less effective. Talk to a pharmacist about interactions.

Morning after pill effectiveness: real numbers and what they mean

People search for how effective the “morning after pill” is because the term covers more than one drug. The two main pills are levonorgestrel (Plan B) and ulipristal acetate (ella). Effectiveness depends on type, timing, and the person’s weight.

Ulipristal (ella): When taken within 120 hours (5 days) of unprotected sex, ella generally prevents more pregnancies than levonorgestrel across that time window. Studies suggest ella maintains relatively stable effectiveness across the 5 days, while levonorgestrel’s effectiveness declines with time.

Levonorgestrel: Best within 72 hours, effectiveness drops with time. If taken right away, it provides meaningful reduction in pregnancy risk, but not as much as ella.

Numbers to expect. No EC pill guarantees prevention. Copper IUD pregnancy rates are under 1% when used as EC. Ella’s failure rates are lower than levonorgestrel in pooled studies, though absolute pregnancy risk depends on when you take it. When possible, assume a nonzero residual risk and take a pregnancy test if your period is more than a week late.

Mistakes people make. Waiting to see if they get pregnant, using the wrong pill, or using a second levonorgestrel dose instead of switching to ella or IUD. If you vomit within two hours of taking a pill, repeat dosing or get another dose from a pharmacy or clinic.

ella vs Plan B: how to choose between them

When deciding between ella and levonorgestrel, weigh timing, weight, drug interactions, access, and cost.

Ulipristal (ella): Prescription-only in many places, active up to 120 hours, more effective later in the 5-day window, and appears less sensitive to body weight than levonorgestrel. It can interact with certain medications that speed up liver enzymes, lowering its effect. If you are taking an enzyme-inducing drug, ella may be less effective or you may need the IUD instead.

Levonorgestrel (Plan B and generics): Available over the counter without age restriction, best within 72 hours, inexpensive and widely stocked. Less effective if you are overweight, and enzyme-inducing drugs can reduce effectiveness. It is a good immediate option if you cannot get a prescription quickly.

Practical choice guide. If you can get ella quickly and are within five days, ella is usually the better pill choice. If you are within 72 hours and need something immediately and access to a prescription is a barrier, levonorgestrel is acceptable. If you are close to or past ovulation, or weight and medication interactions make pills less reliable, the copper IUD is recommended.

Copper IUD emergency contraception: procedure, timing, and pros and cons

What it is. The copper IUD is a small T-shaped device inserted into the uterus by a clinician. As emergency contraception, it can be inserted up to five days after unprotected sex or up to five days after the earliest estimated ovulation day.

Why it’s the most effective. The copper IUD prevents pregnancy with failure rates under 1 percent when used as EC. It works even if ovulation has already occurred because it prevents fertilization and may interfere with implantation.

Insertion process. A trained clinician performs a pelvic exam, measures the uterus, and inserts the IUD in a brief office visit. Expect cramping during and for a day or two after insertion. If you have never had a pelvic exam or IUD before, clinics like Planned Parenthood, sexual health clinics, or family planning services can help.

Pros and cons. Pros: highest effectiveness, provides ongoing contraception for 10+ years depending on device, and does not rely on weight. Cons: requires a clinic visit for insertion, can increase menstrual bleeding and cramps in some people, and has small risks such as perforation or infection at insertion. If heavier periods are a concern, see our article on copper IUD heavy periods.

Follow-up and removal. You can remove the IUD at any time. Ask your clinician how long the specific copper IUD brand is effective, and check strings as described in our IUD strings guide.

How weight matters for emergency contraception pills

Body weight and BMI influence the effectiveness of EC pills, particularly levonorgestrel. Research shows that levonorgestrel’s effectiveness declines as weight increases, and some pooled analyses indicate a statistically significant reduction in protection above certain weight or BMI thresholds.

What the guidelines say. Different agencies vary slightly, but many recommend considering ulipristal or the copper IUD if you have higher body weight or BMI, because those options are less affected by weight. The exact weight cutoff is not universally agreed on; studies report possible reduced levonorgestrel effectiveness starting around 155–176 pounds, but confidence intervals and study designs differ.

Why this happens. Pills are systemic drugs that distribute through the body; greater body mass can reduce peak concentrations and duration of effective drug levels. Ulipristal’s mechanism and potency appear less vulnerable to this effect, and the copper IUD acts locally in the uterus and is not affected by weight.

What to do in practice. If you weigh more than about 165 pounds or have a BMI over 25–30 and are choosing between pills, try to get ulipristal or a copper IUD. If you already took levonorgestrel and your weight is a concern, consider a visit to a clinic for copper IUD insertion as backup, and take a pregnancy test at the appropriate time if your period is late.

What bleeding after emergency contraception means

Light bleeding or spotting after EC pills is common and usually not serious. It is a side effect of the hormonal changes the pill causes. The timing and pattern can vary by method.

After levonorgestrel or ella. You may get spotting in the days after the pill, and your next period might come earlier or later than usual, and might be heavier or lighter. These changes typically normalize within one cycle. If your period is more than a week late, take a pregnancy test.

After copper IUD insertion. Expect cramping and heavier periods for the first few cycles for many people. If you experience very heavy bleeding or severe pelvic pain after insertion, contact the clinic because those could be signs of complications.

When bleeding is a red flag. Heavy bleeding soaking a pad or tampon every hour for several hours, fever and severe pain after insertion, or ongoing bleeding that seems much heavier than your normal period warrant medical attention. For a symptom-by-symptom guide on urgency, see our when-to-seek-care resources.

Where to get emergency contraception fast

Speed matters for EC, so know your local options before you need them. Each option has different access routes, cost, and timing.

Levonorgestrel (Plan B) availability. Over the counter at pharmacies, grocery store pharmacies, and some vending machines. No prescription is needed, and many clinics and community organizations provide them for free or low cost.

Ulipristal (ella) availability. Prescription-only in many countries. You can get it from a clinician, urgent care, telehealth, or sexual health clinic. If you cannot get to a prescriber quickly, some telehealth services can prescribe and ship the pill the same day.

Copper IUD availability. Requires a clinic visit for insertion. Planned Parenthood, community health clinics, sexual health clinics, and many primary care or gynecology offices offer same-day insertion if they have stock and availability. Calling ahead to confirm providers who offer emergency IUD insertion reduces delay.

Other places to try. Hospital emergency departments can insert copper IUDs, though not every ED does. Some pharmacies can order or advise where to obtain ella. If cost is a concern, community clinics, sexual health clinics, and some public health programs provide EC at reduced cost.

Practical tips. If you are unsure what to do right away, get levonorgestrel from a nearby pharmacy while you arrange a prescription for ella or an appointment for a copper IUD, because levonorgestrel is immediate and widely available. If you are able to reach a clinician quickly and want the highest protection, opt for the copper IUD.

Side effects, interactions, and who should not use each option

All EC options have potential side effects and interactions that matter for choice.

Levonorgestrel side effects and cautions. Common side effects include nausea, fatigue, dizziness, breast tenderness, and irregular bleeding. If you vomit within two hours of taking the pill, repeat dosing. Avoid relying on levonorgestrel if you take enzyme-inducing medications, and consider alternatives if you have severe liver disease.

Ulipristal side effects and cautions. Common side effects include headache, nausea, abdominal pain, and fatigue. Ella may interact with enzyme-inducing medications and some hormonal contraceptives; specifically, avoid starting certain hormonal contraceptives for a few days after ella; follow prescriber instructions. Ella is not recommended if you are already pregnant.

Copper IUD side effects and cautions. Possible increased menstrual bleeding and cramps. Not recommended if you have active pelvic infection, an undiagnosed abnormal vaginal bleeding, or certain uterine anomalies. Discuss copper allergies and potential risks with the inserting clinician. If you have heavy periods normally, the copper IUD may worsen bleeding; read our piece on copper IUD heavy periods for more.

Mood and emotional effects. Pills can cause transient mood changes in some people. If you have a history of mood disorder and are concerned about side effects of repeated hormonal doses, discuss options with a clinician. For ongoing contraception decisions, our comparison of options and method pages can help you weigh mood and other effects.

Practical steps to take right now after unprotected sex

• Time-stamp the event. Note the date and time of unprotected sex so you can select the fastest, most effective option.
• Decide on access. If you can reach a clinic quickly and want the most effective protection, call for a copper IUD insertion. If you need something immediately, buy levonorgestrel now and arrange a follow-up for ella or IUD if concerned about weight or timing.
• Check for interactions. Tell the pharmacist or clinician about all medications you take, including herbal supplements like St. John’s wort and anticonvulsants, which can reduce pill effectiveness.
• If you vomit after a pill. Repeat the dose if vomiting occurs within two hours. Contact the provider or pharmacist for guidance.
• Follow-up. Take a pregnancy test if your next period is more than one week late. If you choose an IUD or ella, book routine contraception if you want ongoing birth control.

For help weighing options or finding a clinic, talk to Sarah, the Periodwise assistant for local resource suggestions and next steps.

When to see a doctor about emergency contraception

If you have symptoms or a situation that could be urgent, seek care now.

• Severe pelvic pain after IUD insertion, fever, or heavy bleeding
• Passing large clots with fainting or dizziness
• Signs of pregnancy after EC, like missed period plus pregnancy symptoms
• Vomiting within two hours of taking an EC pill and unable to get a replacement dose
• Signs of infection such as fever, bad-smelling discharge, or severe pelvic tenderness

Book a routine appointment if you have:

• Questions about starting ongoing contraception after EC
• Concerns about repeated need for EC or contraceptive failure patterns
• Need for counseling about mood or side effects of hormonal options
• Desire to talk about fertility timing after EC use

If you are unsure whether your symptoms are an emergency or can wait, our when-to-seek-care guide walks through symptom-level decisions, or chat with Sarah, the Periodwise assistant for quick triage and local referral.

Frequently asked questions

How soon after sex should I take emergency contraception?

Take emergency contraception as soon as possible, because all methods work best the earlier you start. Levonorgestrel works best within 72 hours, ulipristal works up to 120 hours, and the copper IUD can be inserted up to five days after sex.

Can I use emergency contraception if I am breastfeeding?

Yes, levonorgestrel is considered safe while breastfeeding; ulipristal may be used but discuss timing with a clinician and consider temporary breastfeeding interruptions if advised. The copper IUD is also safe during breastfeeding, though you will need a clinic visit for insertion.

Will emergency contraception cause an abortion if I am already pregnant?

No, emergency contraception will not terminate an existing pregnancy. EC works mainly by delaying or preventing ovulation or by preventing fertilization. If you think you might already be pregnant, talk to a clinician about your options.

Can I use two doses of Plan B to increase effectiveness?

Taking two doses of levonorgestrel is not proven to increase effectiveness and is not a substitute for choosing ulipristal or a copper IUD when levonorgestrel is likely to be less effective. If you are concerned about effectiveness, contact a clinician about ulipristal or an IUD.

What if I vomit after taking an emergency contraception pill?

If you vomit within two hours of taking a pill, contact a pharmacist or clinician and repeat the dose if advised. For ulipristal or levonorgestrel, repeating the dose is standard advice when vomiting occurs very soon after ingestion.

How long after emergency contraception should I take a pregnancy test?

Wait until your next expected period; if your period is more than one week late, take a pregnancy test. Some pregnancy tests are sensitive earlier, but a missed period gives the most reliable result.

Can I get pregnant the same week after using emergency contraception?

Yes, there is a small residual risk of pregnancy after EC, which is why follow-up testing is important if your period is late. The copper IUD provides the highest protection and also offers ongoing contraception to prevent pregnancy from future intercourse.

Does weight affect all emergency contraception equally?

No, weight seems to reduce the effectiveness of levonorgestrel more than it does ulipristal. The copper IUD is not affected by body weight, which is why it is the preferred option when weight is a concern.

Where can I get a copper IUD inserted quickly?

Planned Parenthood, sexual health clinics, and many family planning or gynecology offices offer same-day or rapid appointments for copper IUD insertion, depending on stock and provider schedules. Emergency departments may insert IUDs in some hospitals. Use telehealth or call clinics to confirm availability.

Can emergency contraception affect future fertility?

No, there is no evidence that using emergency contraception harms long-term fertility. The copper IUD and EC pills do not reduce your ability to get pregnant in the future once removed or after the drug has cleared.