Can Plan B Cause an Ectopic Pregnancy or Infertility?

Emergency contraception like Plan B One-Step (levonorgestrel) is often used to prevent pregnancy after unprotected sex or contraceptive failure. Questions about safety and long-term effects—especially whether Plan B can cause an ectopic pregnancy or infertility—are common. Here’s what the science and reputable health organizations tell us.

How Plan B Works

Plan B One-Step contains a high dose of levonorgestrel, a synthetic hormone that:

• Delays or prevents ovulation (the release of an egg from the ovary)
• May thicken cervical mucus, making it harder for sperm to reach an egg
• Has no effect on an existing pregnancy

It must be taken within 72 hours (ideally as soon as possible) after unprotected intercourse. The sooner it’s taken, the more effective it is at preventing pregnancy.

Common Plan B Side Effects

Most people handle Plan B without major issues. Side effects usually start within a few hours or days and resolve on their own. Common plan b side effects include:

• Nausea or vomiting
• Headache or dizziness
• Fatigue or tiredness
• Breast tenderness
• Abdominal (lower belly) pain or cramps
• Irregular bleeding or spotting before the next period
• Changes in the timing of the next menstrual cycle (earlier, later, lighter or heavier)

If you vomit within two hours of taking Plan B, contact a healthcare provider. You may need a repeat dose to ensure effectiveness.

Does Plan B Increase the Risk of Ectopic Pregnancy?

An ectopic pregnancy occurs when a fertilized egg implants outside the uterus—most often in a fallopian tube. Untreated ectopic pregnancy can be life threatening.

Here’s what you need to know:

• Plan B does not cause an ectopic pregnancy.
• Emergency contraception works before fertilization; it cannot disrupt an existing pregnancy.
• If Plan B fails and you become pregnant, the overall chance of that pregnancy being ectopic is the same as if you had not taken emergency contraception.
• In other words, Plan B does not increase your baseline risk of ectopic pregnancy.

Warning signs of ectopic pregnancy (seek medical care immediately):

• Sharp or stabbing abdominal pain on one side
• Vaginal bleeding or spotting
• Shoulder pain (referred pain from internal bleeding)
• Weakness, dizziness or fainting

Does Plan B Affect Long-Term Fertility?

There’s no credible evidence that a single dose of levonorgestrel emergency contraception impairs future fertility. Major points:

• Fertility typically returns quickly—often within the next normal menstrual cycle.
• Studies following women who used Plan B show no increase in time to next pregnancy or in infertility rates.
• Plan B does not cause permanent damage to reproductive organs.

If you’re planning pregnancy in the future, rest assured that using Plan B when necessary will not make it harder to conceive later.

When to Seek Medical Advice

Most plan b side effects are mild and resolve without treatment. However, contact a healthcare provider or go to the emergency department if you experience:

• Severe abdominal pain that doesn’t improve
• Heavy vaginal bleeding (soaking through a pad every hour for two hours)
• Signs of allergic reaction (hives, swelling of the face or throat, difficulty breathing)
• Vomiting within two hours of taking Plan B (you may need a repeat dose)
• No period within three weeks after taking Plan B (to rule out pregnancy)
• Any symptom that feels life threatening or very concerning

You can also try a free, online symptom check, using the doctor approved Ubie Symptom Checker to get personalized guidance right away.

Tips for Safe Use of Plan B

• Take it as soon as possible—ideally within 12 hours, and no later than 72 hours after unprotected sex.
• If you’re on certain medications (like enzyme-inducing antiseizure drugs), effectiveness may be reduced. Ask a doctor if you’re unsure.
• Plan B does not protect against sexually transmitted infections (STIs). Use condoms or get tested if needed.
• Keep a supply on hand so you don’t have to scramble to find it in an emergency.

Remember: Plan B is a backup, not a regular contraceptive. Talk to your healthcare provider about a reliable ongoing birth control method that fits your lifestyle.

Final Thoughts

Plan B is a safe, effective way to reduce the risk of unintended pregnancy after contraceptive mishaps. The evidence is clear that it neither causes ectopic pregnancies nor leads to infertility. Most side effects are mild and temporary. If you ever feel something is seriously wrong, don’t hesitate—speak to a doctor about any life-threatening or serious concerns. And for quick guidance on symptoms, consider a free, online symptom check, using the doctor approved Ubie Symptom Checker.

Always rely on trusted medical advice and reach out to your healthcare provider whenever you have questions about emergency contraception or your reproductive health.