If the condom, the pill, or hey, no protection at all has failed your pregnancy prevention plans, you might resort to Plan B.

After taking an emergency contraception (EC) — aka morning-after pill — like Plan B One-Step it’s normal to eagerly await a sign this backup method did its thing. For once, you can’t wait for your period to show up! But what if your flow is still on the fritz?

Here’s what to know about how EC can affect your period.

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Photography by Megan Madden/Prop Styling by Sara Schipani

If you’re staring at the clock waiting for your period to show up, we feel you.

Even though EC can cause your period to come at any time from a week early to a week late, everyone’s different. It’s possible that it can take even longer for your flow to return. But after about 2 weeks, the chance you’re actually pregnant goes up.

What’s to blame for the delay? That extra-strong dose of levonorgestrel (a type of synthetic progesterone — aka progestin). Though some hormonal birth control pills also contain levonorgestrel to prevent pregnancy, the morning after pill has it in much higher quantities. This can do a number on your menstrual cycle, including delaying your period.

In a 2007 study, researchers found that about 15 percent of participants who took Plan B experienced significant changes in menstrual cycle length, period length, and menstrual appearance.

Here’s what might happen when you get your flow back.

Timing and delays

After EC, your period might come late, early — or right on time. Remember, on average, it’s no more than a week either way.

Research from 2006 suggests that the earlier in your cycle you take Plan B, the earlier your next period will be. But the research isn’t conclusive so we don’t know if this is 10/10 true for all EC users.

Period duration

That same 2006 study found that taking EC can make your period last longer than normal. This was the case if the morning after pill was taken after ovulation. Your period length might also stay exactly the same.

Flow intensity

Your post-Plan B period might be lighter or heavier than usual.

According to an FDA report, about 31 percent of women experience heavy flows after taking Plan B. Heavier bleeding is even more likely if you’ve taken the pill more than once in a month.

Extra symptoms

Plan B can cause side effects like nausea, cramps, or headaches, but these symptoms should go away within 24 hours. If cramping persists, it’s likely just your period.

If you have a heavier period after taking Plan B, you might feel extra tired or lethargic.

To make matters more bloody confusing, it’s normal to experience some spotting or light bleeding after Plan B that’s not actually your period. This is a normal side effect of those extra hormones.

Here’s how to *spot* the difference between your period and Plan B bleeding:

  • Keep tabs on timing. Plan B bleeding usually starts flowing a few days after taking the pill.
  • Pay close attention to duration. Plan B spotting usually only lasts a day or 2, but it’s possible that it could last a little longer.
  • Super light bleeding. Spotting won’t look exactly like your usual period. It’s usually a much lighter color and it might only be a few drops of blood.
  • Check out the signs and symptoms. It’s unlikely you’ll experience all of your regular period probs like serious cramps and mood swings. However, Plan B can come with other side effects that usually disappear after 24 hours like:

PSA: In rare cases, spotting could also signal an early pregnancy, so track your cycle and take a pregnancy test if you feel unsure.

Most likely, your period will be business as usual by your second cycle after Plan B.

In a 2007 study, researchers found that the majority of participants who initially experienced menstrual changes from EC didn’t experience recurring symptoms in their second period.

Plan B is 95 percent effective if taken within a day after sex and 88 percent if taken between 3 days after. But there’s always a slim chance it won’t work.

If you take Plan B and your period is over a week late, there’s a slight chance that you might be pregnant. Take a pregnancy test to play it safe.

If it’s been 2 weeks, your pregnancy odds are even greater and you should likewise take a test. If your pregnancy test is positive, visit a doctor or midwife to confirm your result and walk you through your options.

If you’re not sure what stage of your cycle you’re at or you have irregular periods, Planned Parenthood recommends waiting 3 weeks after taking Plan B before you take a pregnancy test.

Pregnancy tests measure the hormone human chorionic gonadotropin (hCG), which the body starts to produce a few days after conception. So if you take a test too early, it could show a false-negative result.

If your period is still MIA 2 months after taking Plan B, you could be pregnant. It’s unlikely it’s the EC still messing with your cycle.

Take a pregnancy test and visit a doctor or midwife ASAP to know for sure.

Other things that can delay your period include:

Plan B impacts everyone differently, so it’s tough to predict how it will affect your menstrual cycle.

If your first period after taking EC is a few days earlier or later than normal, it’s probably nothing to worry about. After a week, take a pregnancy test.

By your second period post-Plan B, everything should return to normal. If you’re still experiencing irregular periods, talk with your doc.