Emergency Contraception: Side Effects, Timing, and When to See a Doctor
How emergency contraception works, common side effects (nausea, bleeding, cycle changes), effectiveness windows, and when to take a pregnancy test or seek care.
Important safety information
This article explains how certain products work and common side effects. It does not replace professional medical care. Seek urgent care for severe pain, heavy bleeding, fainting, chest pain, trouble breathing, or any symptom that worries you. For poisoning questions, call Poison Control at 1-800-222-1222 (U.S.).
Quick answer
Emergency contraception (EC) is for backup after unprotected sex or contraceptive failure — not regular birth control. Most side effects are mild and short-lived: nausea, headache, fatigue, and a shifted next period. Take a pregnancy test if your period is a week late. EC works best the sooner you take it; it does not replace ongoing contraception or STI prevention.
What emergency contraception is (and is not)
Emergency contraception refers to methods used after sex to reduce the chance of pregnancy. Common options include:
- Levonorgestrel pills (often called “Plan B”-type products) — most effective within 72 hours; some benefit up to 120 hours
- Ulipristal acetate — prescription pill effective up to 120 hours after sex
- Copper IUD — placed by a clinician; most effective form of EC when inserted within 5 days
These are not abortion medications. They primarily delay or prevent ovulation. If pregnancy has already implanted, EC will not end it.
Common side effects
Most people tolerate EC well. Typical short-term effects include:
- Nausea or vomiting — more common with levonorgestrel; taking with food may help. If you vomit within 2–3 hours of the dose, call a pharmacist or clinician — you may need another dose.
- Fatigue and headache — usually resolve within 24–48 hours
- Breast tenderness or bloating
- Dizziness
- Changes to your next period — earlier, later, heavier, lighter, or spotting. This is common and often settles by the following cycle.
When side effects need medical attention
- Severe abdominal pain — especially if localized to one side (ectopic pregnancy must be ruled out if pregnant)
- Heavy bleeding (soaking through a pad every hour for several hours)
- Signs of allergic reaction (hives, swelling, trouble breathing)
- Persistent vomiting preventing hydration
- Any symptom that feels severe or unusual for you
Emergency: 911 (U.S.) for chest pain, trouble breathing, or fainting. Poison Control: 1-800-222-1222 for overdose or dosing questions.
Effectiveness and timing
EC is not 100% effective. Effectiveness drops the longer you wait. Body weight may reduce effectiveness of some pill forms — ask a pharmacist or clinician about the best option for you (ulipristal or copper IUD may be preferred in some cases).
EC does not protect against STIs. Testing and safer-sex counseling matter if exposure was unprotected.
What to expect with your cycle afterward
Your next period may come early or late by up to a week or more. Track timing with our ovulation calculator only after your cycle normalizes — irregular bleeding right after EC is expected.
- Take a pregnancy test if your period is more than 7 days late
- Test sooner if you have pregnancy symptoms
- If pregnant after EC, contact your provider promptly for guidance
Drug interactions and repeat use
Some medications (certain anti-seizure drugs, enzyme inducers) may reduce EC effectiveness. Tell the pharmacist everything you take. Check interactions with our drug interaction checker, then confirm with a professional.
EC is intended for occasional use. For regular contraception, discuss pills, patches, rings, IUDs, or implants with your clinician. Repeated EC in one cycle is less ideal than a consistent method.
Emotional and follow-up care
Needing emergency contraception is common and not something to feel ashamed about. If you feel anxious, overwhelmed, or need confidential support, talk to a healthcare provider, campus health center, or Planned Parenthood. Crisis text line: text HOME to 741741 (U.S.).
Planning ahead
If you are trying to conceive later, see our guide on medications that affect fertility and use the due date calculator once you have a positive test and provider confirmation.
Track your cycle privately
Free tools for ovulation timing and pregnancy planning — no account required.
Important safety information
This article explains how certain products work and common side effects. It does not replace professional medical care. Seek urgent care for severe pain, heavy bleeding, fainting, chest pain, trouble breathing, or any symptom that worries you. For poisoning questions, call Poison Control at 1-800-222-1222 (U.S.).