Emergency Contraception: Plan B vs ella vs IUD, How Fast to Take It and How Well It Works
Written by Cherlie Joseph, MSN, FNP-BC · Medically reviewed by Naurah Gaspard, DNP, FNP-C, FNP-BC · Updated November 2026
Emergency contraception lowers the chance of pregnancy after unprotected sex or a birth control mistake. Plan B One-Step (levonorgestrel) is sold over the counter and works best within 72 hours; ella (ulipristal) needs a prescription and works up to 5 days after sex; a copper or hormonal IUD placed within 5 days is the most effective option. None of them end an existing pregnancy.
In this guide
Your three emergency contraception options
| Option | Time window | How to get it |
|---|---|---|
| Levonorgestrel 1.5 mg (Plan B One-Step, Take Action, My Way and other generics) | Best within 72 hours (3 days); sooner is better | Over the counter, no age limit or ID |
| Ulipristal acetate 30 mg (ella) | Up to 120 hours (5 days) | Prescription |
| Copper IUD or 52 mg levonorgestrel IUD | Within 5 days | In-person placement |
Emergency contraception pills work mainly by delaying or preventing ovulation. If you have already ovulated, the pills are much less likely to work, which is why timing matters so much. They do not harm an existing pregnancy and are not the same as the abortion pill.
Which option works best
IUDs are the most effective, preventing more than 99% of pregnancies when placed within 5 days. The CDC's 2024 contraception guidance added the 52 mg hormonal IUD (such as Mirena or Liletta) as an emergency option alongside the copper IUD. A bonus: you leave with years of ongoing birth control.
ella is more effective than levonorgestrel pills, especially on days 3 to 5 after sex, because it can still delay ovulation closer to the time the egg is released.
Levonorgestrel pills are the easiest to get quickly and work best when taken as early as possible. Studies estimate they prevent most expected pregnancies, but their effect drops over time.
Does weight matter?
Some studies suggest levonorgestrel pills may be less effective in people with a higher body weight or BMI of 30 or more, though the evidence is mixed and the FDA has not changed the label. ACOG notes that ella or an IUD may be better options in this situation. If you can't get those quickly, taking levonorgestrel is still better than taking nothing.
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- Side effects are usually mild: nausea, headache, tiredness, breast tenderness, belly cramps or spotting. If you vomit within 3 hours of taking a pill, ask a pharmacist or provider whether to take another dose.
- Your next period may come a few days early or late. If it is more than 7 days late, take a pregnancy test.
- Protection is not ongoing. Emergency pills only cover sex that already happened. You can get pregnant later in the same cycle, so use condoms or start regular birth control.
Emergency contraception does not protect against STIs. If the sex was with a new partner or without a condom, it is worth thinking about STI testing.
Starting regular birth control afterward
The timing depends on which emergency option you used, according to the CDC's 2024 Selected Practice Recommendations:
- After levonorgestrel pills: you can start or restart hormonal birth control right away, and use condoms or avoid sex for the next 7 days (2 days for progestin-only pills).
- After ella: wait at least 5 days before starting or restarting hormonal birth control, because hormones can make ella less effective. Use condoms or avoid sex until you've been on your method for 7 days (2 days for progestin-only pills).
- After an IUD: no extra steps; it keeps working as your birth control.
Taking emergency pills more than once in a cycle is not dangerous, but they are less effective than ongoing birth control. If you've needed emergency contraception more than once, a longer-term method may give you more peace of mind.
Get in-person care or call 911 if you have:
- Severe belly or pelvic pain, especially on one side, or shoulder pain or fainting (possible ectopic pregnancy)
- Very heavy bleeding that soaks a pad every hour for 2 hours or more
- If the sex was not consensual, you can get care, emergency contraception and support at an emergency room
Frequently asked questions
How late can you take Plan B?
Plan B and other levonorgestrel pills are labeled for use within 72 hours and work best the sooner you take them. ella works up to 5 days after sex, and an IUD can be placed within 5 days.
Do I need a prescription for the morning-after pill?
Not for levonorgestrel pills like Plan B One-Step; they are sold over the counter with no age limit. ella requires a prescription.
Will emergency contraception affect my future fertility?
No. Emergency contraception does not affect your ability to get pregnant in the future.
Sources
- ACOG: Emergency Contraception FAQ
- CDC: U.S. Selected Practice Recommendations for Contraceptive Use, 2024
- FDA: Plan B One-Step information
Keep reading
- Birth control options compared
- Missed a birth control pill? What to do
- How soon to get tested after a possible STD exposure
- Browse all conditions and treatments A to Z
Need emergency contraception or a follow-up birth control plan?
$79 visit, no appointment needed. Adults 18+ in FL, NM, OR and WA.
Start a visit →
Cherlie Joseph, MSN, FNP-BC
Board-certified family nurse practitioner licensed in Florida, caring for adults online at OurTopClinic. Meet our providers.
This article is for general education and is not a substitute for medical advice. Treatment, including any prescription, is decided by a licensed provider after reviewing your health history. OurTopClinic is not for emergencies; if you have a medical emergency, call 911. OurTopClinic serves adults located in Florida, New Mexico, Oregon and Washington. Learn more at ourtopclinic.com.
