Emergency Contraception — How It Works, When It Works, and What to Expect

Emergency contraception (EC) is a safe, time-sensitive way to prevent pregnancy after unprotected sex, contraceptive failure (like a broken condom or missed pills), or sexual assault. It is not the same as ongoing birth control — it's a backup option for specific situations.

There are three main types, and they work through different mechanisms:

Plan B and generics (levonorgestrel 1.5 mg) are over-the-counter pills that primarily work by delaying or preventing ovulation. If ovulation has already occurred, levonorgestrel has little to no effect — which is why timing matters so much. It does not disrupt an existing pregnancy or prevent a fertilized egg from implanting (despite outdated label language).

ella (ulipristal acetate 30 mg) is a prescription pill that works similarly by postponing ovulation, but it's more effective than Plan B because it can delay ovulation even when LH levels have already started to rise — a point at which levonorgestrel becomes less reliable. This gives ella a wider effective window.

The copper IUD (Paragard) is the most effective form of emergency contraception. When inserted within 5 days of unprotected sex, it prevents pregnancy by creating an inflammatory environment that is toxic to sperm and eggs, preventing fertilization. It can also be left in place as ongoing contraception for up to 10 years.

Timing is critical for emergency contraception — the sooner you act, the more effective it is. But the exact window depends on which method you use.

Plan B (levonorgestrel) should be taken as soon as possible and is most effective within 24 hours of unprotected sex. It remains reasonably effective for up to 72 hours (3 days), but effectiveness drops significantly with each passing day: roughly 95% effective within 12 hours, 85% within 24–48 hours, and 58% within 49–72 hours. After 72 hours, it offers little reliable protection.

ella (ulipristal acetate) has a wider window — it remains effective for up to 120 hours (5 days) after unprotected sex. Crucially, ella maintains more consistent effectiveness across that entire window compared to Plan B, which declines sharply. If it's been more than 24 hours, ella is the better oral option.

The copper IUD can be inserted up to 5 days after unprotected sex — and its effectiveness doesn't significantly decline across that window. It prevents over 99% of expected pregnancies regardless of whether it's inserted on day 1 or day 5.

Practical takeaway: don't wait. If you need emergency contraception, take action the same day if possible. If Plan B is all you can access quickly, take it immediately. If you have time to see a provider within the 5-day window, the copper IUD offers the strongest protection and doubles as long-term contraception.

Effectiveness varies by method, timing, and body weight — and understanding these differences helps you make the best choice in a time-sensitive situation.

The copper IUD is the gold standard: it prevents over 99% of expected pregnancies when inserted within 5 days. No oral method comes close to this level of effectiveness.

ella prevents approximately 85% of expected pregnancies when taken within 120 hours. Its effectiveness remains relatively stable across the 5-day window, making it the best oral option when more than 24 hours have passed.

Plan B prevents approximately 85% of expected pregnancies when taken within 72 hours, but this is an average. Its effectiveness drops from roughly 95% in the first 12 hours to under 60% by hour 72.

Body weight matters. Research shows that Plan B becomes significantly less effective in women weighing over 165 lbs (75 kg) and may be ineffective above 175 lbs (80 kg). Ella appears to maintain better effectiveness at higher weights, though some reduction has been observed above 195 lbs (88 kg). The copper IUD's effectiveness is not affected by body weight — making it the most reliable option for all body types.

It's important to understand what these numbers mean: EC reduces the risk of pregnancy from a single act of unprotected sex. It does not provide 100% protection, and it does not protect against future unprotected encounters. If you have ongoing contraceptive needs, talk to your provider about a regular method.

Emergency contraception is safe for the vast majority of people, and side effects are generally mild and short-lived. Knowing what to expect can help reduce anxiety about taking it.

Common side effects of Plan B and ella include nausea (the most frequent complaint, affecting about 15–25% of users), headache, fatigue, dizziness, and breast tenderness. Taking the pill with food can reduce nausea. If you vomit within 2 hours of taking it, you may need another dose — contact your pharmacist or provider.

Menstrual cycle changes are the most noticeable effect. Your next period may come earlier or later than expected — typically by a few days to a week. You may also experience heavier or lighter bleeding, spotting between periods, or cramps. These changes are temporary and resolve within one to two cycles.

The copper IUD insertion may cause cramping and spotting at the time of placement. Ongoing effects include potentially heavier periods and increased cramping, particularly in the first few months — these are consistent with the copper IUD's effects as a regular contraceptive method.

Emergency contraception does not have long-term side effects. It does not increase your risk of blood clots, cancer, or ectopic pregnancy. It does not accumulate in your body or cause lasting hormonal disruption. While it's not intended as a primary contraceptive method (because regular methods are more effective), using it more than once is not harmful.

No. Emergency contraception does not affect your future fertility — this is one of the most persistent myths, and the evidence is clear.

Plan B and ella work by temporarily delaying ovulation. Once the medication is metabolized (within days), your normal hormonal cycle resumes. There is no mechanism by which these medications could cause lasting changes to your ovaries, uterine lining, or fallopian tubes. Large population studies have found no association between emergency contraception use — even repeated use — and subsequent difficulty conceiving.

The copper IUD, when used for emergency contraception, can be removed at any time. Fertility returns almost immediately after removal, typically within the first cycle. If you choose to keep it for ongoing contraception, it remains fully reversible — studies show that pregnancy rates after IUD removal are equivalent to those in women who never used an IUD.

The myth that EC harms fertility may stem from confusion with medication abortion (mifepristone), which is an entirely different medication with a different mechanism. Emergency contraception prevents pregnancy from occurring — it cannot disrupt a pregnancy that has already implanted.

Repeated use of emergency contraception is also safe from a fertility standpoint. While it's not recommended as a primary method (because regular contraception is more effective and predictable), using EC multiple times does not cause cumulative harm to your reproductive system. If you find yourself needing EC frequently, it's worth discussing more reliable ongoing options with your provider — not because EC has harmed you, but because a regular method will give you better protection.

No — emergency contraception and medication abortion are completely different medications with different mechanisms, and confusing them leads to unnecessary stigma and barriers to access.

Emergency contraception prevents pregnancy. It works by delaying or inhibiting ovulation so that fertilization never occurs. Plan B (levonorgestrel) and ella (ulipristal acetate) have no effect on an established pregnancy — if you are already pregnant, taking emergency contraception will not harm the pregnancy or cause a miscarriage. The copper IUD prevents fertilization by creating an inhospitable environment for sperm.

Medication abortion (mifepristone and misoprostol, also called the "abortion pill") terminates an existing pregnancy. Mifepristone blocks progesterone receptors, which is necessary for pregnancy maintenance, and misoprostol causes uterine contractions to expel the pregnancy. This is a fundamentally different process that occurs weeks after conception.

The confusion often arises because both involve reproductive health decisions and pills, but the biology is entirely distinct. Emergency contraception acts before implantation — preventing a pregnancy from beginning. Medication abortion acts after implantation — ending a pregnancy that has already been established.

Major medical organizations including ACOG, the WHO, and the American Medical Association classify emergency contraception as contraception, not abortion. This distinction matters for access: emergency contraception remains legal and available in all 50 U.S. states, including states with abortion restrictions.

Access depends on which method you need, where you live, and your insurance coverage — but in most cases, you can get emergency contraception quickly and without significant barriers.

Plan B and generic levonorgestrel are available over the counter in the United States with no age restriction and no prescription required. You can find them at pharmacies, drugstores, and many grocery stores — typically in the family planning aisle or behind the pharmacy counter (ask if you don't see it). Some pharmacies also offer it through self-checkout. Online retailers sell it as well, though shipping time may reduce its effectiveness.

Cost for Plan B ranges from $25–50 for brand name and $10–40 for generics (like Take Action, My Way, or AfterPill). Insurance and Medicaid may cover it, though navigating coverage at the pharmacy counter can cause delays — if cost isn't a barrier, purchasing it directly is often faster.

ella requires a prescription in the United States. You can get a prescription from your doctor, urgent care, Planned Parenthood, or through telehealth services that specialize in reproductive health. Some telehealth platforms offer same-day prescriptions with pharmacy pickup. Ella typically costs $40–60 without insurance.

The copper IUD requires a clinical visit for insertion. Contact your OB-GYN, Planned Parenthood, community health center, or urgent care clinic. If it's being used for emergency contraception, emphasize the time-sensitive nature when scheduling. Cost ranges from $0 with insurance to $500–1,000 without, but many clinics offer sliding scale fees.

Proactive tip: consider keeping a dose of Plan B at home before you need it. Having it on hand eliminates the most critical barrier — time.