Plan B: How it Works, Side Effects, and More

Even if you’re using protection, there’s always a chance that you could get pregnant. Perhaps you’ve turned to Plan B to avoid an unplanned pregnancy. But, what happens if Plan B fails? It’s crucial to understand your pregnancy options so you can plan your next steps!

Today, we’re discussing Plan B—including how it works, the risks and side effects, and what to do if you still get pregnant after taking it. Keep reading to learn more!

How Does it Work?

Plan B is a form of emergency contraception that lowers the risk of pregnancy by preventing or delaying ovulation. It’s often used when birth control fails or in cases of sexual assault.

However, Plan B doesn’t always prevent ovulation,^1,2,3 but may also work by disrupting the hormonal environment and interfering with the embryo’s attachment to the uterus, resulting in its death.^4,5

It’s important to know that Plan B and all other forms of emergency contraception should only be used as backups, not as primary methods of birth control.⁶

Is Plan B an Abortion Pill?

While they seem similar, Plan B and the abortion pill are not the same things. The difference is that Plan B aims to keep you from getting pregnant in the first place and may disrupt a newly formed embryo from continuing to grow⁷, but the abortion pill is designed to end a pregnancy every single time it is used.

If you have been sexually active in weeks prior to taking Plan B you may want to take a pregnancy test or even receive an ultrasound just to be certain that you’re not pregnant from a previous sexual encounter.

Can Plan B Cause Miscarriage?

A miscarriage is an unintended loss of a pregnancy before the 20th week of pregnancy. While the goal of Plan B is to prevent pregnancy altogether, if an embryo has already formed when Plan B is taken, it may interfere with the embryo’s ability to attach to the uterus, resulting in its death.⁸ If that is not your intent, then Plan B may not be for you.

Additionally, the Mayo Clinic warns that taking Plan B while pregnant can harm the fetus.⁹

How Effective is Plan B? When Can I Take Plan B?

Plan B is most effective when taken as soon as possible after having unprotected sex. It is reported to reduce the risk of pregnancy for up to 72 hours, but is not always effective.¹⁰

Does Plan B Have Side Effects?

Common side effects of Plan B include¹¹:

• Dizziness
• Headache
• Cramps or abdominal pain
• Nausea or vomiting
• Breast tenderness
• Delayed period, irregular bleeding, and/or heavier bleeding during your next period¹²

These side effects should be mild and only last a few days. However, if you experience bleeding or spotting for longer than a week or have significant lower abdominal pain after taking Plan B, contact your healthcare provider immediately, to be evaluated for a miscarriage or an ectopic pregnancy .¹³

What to Do if Plan B Fails

If you’ve taken Plan B and missed your period, it could mean that you’re pregnant.¹⁴

The next step is to find out for sure. We can connect you with a local pregnancy center that provides free pregnancy tests, ultrasounds, and options education, so you can take your next steps with confidence!

All of our services are 100% free and confidential. We exist to provide accurate medical information and support to women and men facing an unplanned pregnancy. Our pregnancy centers do not offer or refer for pregnancy terminations or birth control. Information is provided as an educational service and should not be relied on as a substitute for professional and/or medical advice.