Emergency Contraception

Even with protection, unplanned pregnancies can occur. If you’re considering emergency contraception like Plan B or other morning-after pills, it’s important to understand:

  • How it works

  • Effectiveness

  • The risks and side effects

  • What to do if it fails

How Does Emergency Contraception Work?

Emergency contraception (also known as the Morning-After Pill) lowers the risk of pregnancy by preventing or delaying ovulation.

However, emergency contraception doesn’t always prevent ovulation.[1][2][3] If you are already pregnant, it may affect how the embryo attaches to the uterus. This can cause the embryo to die.[3]

Woman talking with doctor about "How Emergency Contraception Works"
Woman wondering "How Effective is Emergency Contraception?"

Types of

Emergency Contraception

  • Plan B One-Step® (Levonorgestrel). Plan B is the most widely available over-the-counter emergency contraceptive. This progestin-only pill is most effective when taken within 72 hours of unprotected sex.  
  • ella® (Ulipristal Acetate). ella® is a prescription emergency contraceptive, a chemical cousin to mifepristone (part of the abortion pill protocol).[4][5] ella® is effective up to five days after unprotected sex.

How Effective Is Plan B and Other Emergency Contraceptives?

  • Pregnancy is only possible during a woman’s fertile part of her cycle (about 7 days). Taking emergency contraception at other times will have not impact pregnancy risk.
  • Plan B works best when taken right after unprotected sex. It can lower pregnancy risk for up to 72 hours.[6] 
  • Ella can be taken up to five days after unprotected sex. However, research suggests that emergency contraception tends to be less effective in women who are overweight.[7]
Woman writing down the differences between emergency contraception and the abortion pill

Emergency Contraception vs. Abortion Pill:
Key Differences

While often confused, Plan B and the abortion pill serve different purposes:

  • Emergency contraception aims to prevent pregnancy from occurring, but, depending upon where a woman is her cycle, it may not prevent a pregnancy from forming, but it may disrupt a newly formed embryo’s continued development and growth.[8]
  • The abortion pill is specifically designed to end a pregnancy that has already started.

If you’ve been sexually active in recent weeks, consider taking a pregnancy test before using emergency contraception. This helps confirm you aren’t already pregnant from an earlier encounter. If you do not want to end a pregnancy that has already started, emergency contraception may not be right for you. 

 

Woman searching on her phone "Can Emergency Contraception Cause Abortion?"
Woman wondering "What are the Risks and Side Effects of Emergency Contraception?"

Can Emergency Contraception Cause Miscarriage?

If fertilization has already occurred when emergency contraception is taken, the medication may interfere with the embryo’s ability to implant in the uterus, potentially resulting in its loss.[8] 

If that is not your intent, then emergency contraception may not be for you. 

Risks & Side Effects of
Emergency Contraception

Common side effects of emergency contraception include[9]:

  • Dizziness
  • Headache
  • Fatigue
  • Cramps or abdominal pain 
  • Nausea and/or vomiting
  • Breast tenderness
  • Delayed period (up to a week), heavier bleeding during your next period, or bleeding between periods

These side effects are typically mild and temporary. However, seek immediate medical attention if you experience severe lower abdominal pain, which could indicate an ectopic pregnancy.

    Nurse explaining to a woman What to Do if Your Emergency Contraception Fails
    Woman wondering "How Effective is Emergency Contraception?"

    What to do if

    Emergency Contraception Fails

    If your period is late by more than three to four weeks after taking emergency contraception, you may be pregnant.[7] Don’t panic—you have options and support available.

    Care Net Women’s Resource Center of North County is here to help you make a safe and informed decision. We offer:

    • Free pregnancy testing 
    • Free ultrasounds / Ultrasound referrals
    • Pregnancy options education
    • Confidential, compassionate care
    • Resources to help you move forward with confidence

    Give us a call at 661-729-4277 or make an appointment online today. All services are confidential and free of charge.

    *Important notes: Care Net Women’s Resource Center of North County provides pregnancy testing, ultrasound, and options education. We do not provide or refer for emergency contraception or abortion services. Our goal is to support you with accurate information and compassionate care as you make decisions about your reproductive health.

    Additionally, this article is not meant to substitute for medical advice or treatment. The purpose of our limited ultrasound exams is to identify a pregnancy inside the uterus, detect the fetal heartbeat, and estimate how far along you are. If there is no detectable heartbeat, it may indicate a miscarriage or ectopic pregnancy is occurring. If we cannot detect a fetal heartbeat during your appointment, we will provide appropriate referrals for follow-up care and treatment.

    Sources

    1. Hapangama D, Glasier AF, Baird DT. “The effects of peri-ovulatory administration of levonorgestrel on the menstrual cycle.” Contraception. 2001 Mar;63(3):123-9. DOI:10.1016/s0010-7824(01)00186-x https://www.contraceptionjournal.org/article/S0010-7824(01)00186-X/fulltext
    2. Croxatto, HB, Brache V, Pavez M, Cochon L, Forcelledo ML, Alverez F, Massai R, Faundes A, and Salvatierra AM, 2004. “Pituitary-ovarian Function Following a Standard Levonorgestrel in Emergency Contraception Dose or a Single 0.75 mg Dose Given on the Days Preceding Ovulation.” Contraception. 2004 Dec;70(6):442-50. DOI:10.1016/j.contraception.2004.05.007 https://www.contraceptionjournal.org/article/S0010-7824(04)00156-8/fulltext
    3. AAPLOG Committee Opinion #7. (2020, January). Embryocidal Potential of Modern Contraceptives. https://aaplog.org/wp-content/uploads/2024/05/Committee-Opinion-7-updated.pdf 
    4. Physician’s Desk Reference. (2023, April 13). Ella Drug summary: Mechanism of action. https://www.pdr.net/drug-summary/?drugLabelId=1278
    5. Saritha, F., Aiswarya, N., Aswath Kumar, R., & Dileep, K. V. (2023, February 3). Structural analysis and ensemble docking revealed the binding modes of selected progesterone receptor modulators. Journal of Biomolecular Structure & Dynamics. https://pubmed.ncbi.nlm.nih.gov/36752314/
    6. Mayo Clinic. (2024, September 1). Levonorgestrel (Oral Route) Side Effects. https://www.mayoclinic.org/drugs-supplements/levonorgestrel-oral-route/side-effects/drg-20074413
    7. Mayo Clinic. (2022, June 3). Morning-after pill. https://www.mayoclinic.org/tests-procedures/morning-after-pill/about/pac-20394730#
    8. Kahlenborn, C., Peck, R., & Severs, W. B. (2015). Mechanism of action of Levonorgestrel emergency contraception. The Linacre Quarterly, 82(1), 18-33. https://doi.org/10.1179/2050854914y.0000000026
    9. Cleveland Clinic. (2022, July 1). Morning-After Pill: Emergency Contraception & Side Effects. https://my.clevelandclinic.org/health/treatments/23386-morning-after-pill
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