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Dr, How Do I Know If the Morning After Pill Worked Effectively?

June 19, 2021

Have you ever asked yourself how to know if the morning-after pill worked? If you took the morning after pill and then spent days agonising over whether it worked or not before you could do a pregnancy test, then keep reading! And believe me, there are many other women and couples with this same question so it’s obviously something we need more information about!

Did The Pill Work?

Many women use emergency contraception pills to avoid unplanned pregnancies.

One of the issues with the pill is the question of whether it’s worked after you use it.

 Here’s a question I got just yesterday about this very issue:

Hi, doc my last menses started around 18th and ended around 23rd last month…I had unprotected sex on the 6th and took m.a.p on the 8th.. been feeling weird but I started bleeding today morning…Can I be pregnant by any chance?

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Without tests, the earliest sign most women of pregnancy is when they miss their period.

Commonly, as early as 5-6 weeks after their missed period, most women will begin to experience pregnancy symptoms.

Earliest Signs of Pregnancy

Some of these symptoms could even happen BEFORE the period is missed, such as :

  • Nausea and sometimes being unable to keep any food down
  • Sensitive, aching or sore breasts
  • Feeling more tired than expected.
  • A higher-than-usual basal body temperature
  • Unusual vaginal bleeding – you may have some vaginal spotting or what appears to be a lighter period than usual – also known as implantation bleeding. (“Implantation bleeding usually occurs about a week before your expected period. The bleeding will be a lot lighter than your usual period. It will stop after one to three days. This is light spotting or bleeding that occurs about 10 to 14 days after conception, usually about a week before your period would usually start. This bleeding will be lighter and stop after one to three days”.) 

But even before that, the earliest time you can detect pregnancy is about one week after sex with a blood test (roughly 6-11 days with the most sensitive tests); looking for Beta HCG (BHCG), one of the earliest hormones that start to go up after you fall pregnant.

Of course, blood tests are more sensitive than urine tests.

And so the earliest most urine tests will be positive for BHCG is two-three weeks after sex.

So if you are relying on a home pregnancy test, which is the case for most women, that still leaves at least 10-14 days after sex when you or you and your partner are unsure whether you are pregnant or not.

This creates a considerable period of uncertainty and can be pretty distressing for some couples.

 And it means that if a woman has taken the pill to prevent pregnancy, she’ll be looking for every sign possible to reassure herself that it has worked.

Morning After Pill - Sperm attempting fertilisation of Egg

Becoming Pregnant – The Essentials

So, to work out how to tell if the pill has worked, it’s helpful to know what it does in your body.

Before that, let’s look at what needs to be in place for you to fall pregnant.

Most of the time, you don’t get pregnant the very instant you have sex. 

If you have just ovulated, then the sperm and egg may fertilise in a short while.

But if you haven’t yet ovulated, sperm may remain for some days in the womb, waiting for the ovary to release the egg. 

For most women with a regular 28-day cycle, you are more likely to get pregnant in the first half of your cycle.

Usually, this is after your period ends and up to 1 day after ovulation. Those dates are known as your fertile window

When released, your egg will live about 24 hours. On the other hand, after ejaculation, healthy sperm can live up to 7 days within a woman’s womb. 

Even when you have not yet ovulated during your fertile period, having sex is most likely to lead to pregnancy.

The sperm can stay alive for seven days, waiting for your ovary to release a mature egg. So you can have sex one week before ovulation and still fall pregnant. 

 And this is where the emergency pill comes in useful.

How Does the Morning After Pill Work?

Well, the primary way modern emergency contraception pills work is to delay ovulation.

This means that if you had sex before ovulation and took the EC pill, it would delay the process by about 5-7 days till the sperm from that episode of sex has likely died before the egg is released.

 I say primarily because the drugs can also have some other effects on the body:

  1. They can make the mucus within the womb (cervical mucus) thicker and slow down the sperm’s ability to swim within the womb to reach the egg.
  2.  They could even affect the lining or tissues of the womb, preventing the fertilised egg from fixing within the womb. (implantation).

However, according to studies, these two methods are not as effective, so the one method we are pretty sure of how the pill works is by delaying your ovulation.

Fertile Window in Emergency Contraception

Morning After Pill Side Effects

Already we’ve seen that after having sex, you’re left with roughly two weeks, during which you need to wait to find out if you are pregnant.

But if you’ve taken the pill after sex, is there any way to know if the emergency pill has worked during that 2-week waiting time?

Well, the answer is NO – there is NO way you can tell it worked till you either get your period or do a pregnancy test. 

Some women say they feel different – their breasts feel different, or they experience bleeding after using the pill.

However, you can’t rely on these symptoms to guide you one way or the other.

  1. You may feel different due to the effect of the external hormones contained in the pill. 
  2. Bleeding soon after taking the EC pill could suggest other things.
  • it could be a side effect of the pill
  • It could be your period which the pill has caused to happen a little earlier than expected

But it never indicates whether or not the pill has worked.

Therefore, you will have to be patient for those two weeks after sex, which is the earliest period till you can have a negative blood or urine PT.

Read here about Delayed periods after taking Plan B.

How To Know If The Morning After Pill Has Worked

Can You Get Pregnant After Taking The Morning After Pill?

Yes, you can still fall pregnant after taking the pill.

Most often, this happens if you take the pill during or after you’ve already ovulated.

Or, you’ve taken the pill at the right time, yet you vomited just afterwards.

In addition, delaying how soon after sex you take the pill can also lead to failure (see below).

Here’s just what to do to reduce the risk of the pill not working:

  1. Know your cycle – use a calendar or app to identify your fertile period and estimate when you ovulate. If you are not on regular contraception, this helps you know the safe period when you are less likely to fall pregnant though I would still recommend using a condom or pill if you are not sure. 
  2. If you have sex, and it’s definitely around ovulation or your fertile window, take the pill asap after sex.
  3. Carefully follow the instructions on the pack; you are less likely to have anxious days and nights if you take the pill at the right time and in the proper doses – it will do its job effectively. For example, here are some pill facts. MAPs that contain Levonorgestrel (like Postinor, Take Action or Plan B) prevent:
  • from up to 95% of pregnancies if taken within 24 hours
  • up to 85% if taken within 25-48 hours
  • up to 58% if taken within 49-72 hours

For this reason, taking Levonorgestrel three days after unprotected sex may not leave you as well-protected as you hoped. 

On the other hand, the other EC pill, Ulipristal, the most effective morning-after pill, remains up to 98% effective throughout the five-day window. This is unlike LNG, whose effectiveness begins to reduce from 12 hours after sex. So not only do you have a longer window of 5 days after sex to use Ulipristal, but it is also slightly more effective at delaying ovulation than LNG.

You can learn more about Ulipristal here.

  1. If you’ve not been able to take the pill or are very worried it’s not worked, you do still have an option within five days of sex or your ovulation to have the Copper Copil or Copper IUD.
  2. The Copper coil is the most effective emergency contraception method presently available.

Safe Contraception

Taking contraception safely means you need to be a little more aware of your body and events that happen at special times.

Hopefully, this article explains all you need to know but guess what: you can send us an email or leave a response in the comments if you need any more answers.

 Stay Well!

More Reading


  1. FSRH Emergency Contraception
  2. Morning After Pill Effectiveness | LloydsPharmacy Online Doctor 
  3. UKHow Long Do You Ovulate & How Long Does an Egg Last After Ovulation – BEAUTY SIGHT

Editing by AskAwayHealth Team


All AskAwayHealth articles are written by practising  Medical Practitioners on a wide range of healthcare conditions to provide evidence-based guidance and to help promote quality healthcare. The advice in our material is not meant to replace the management of your specific condition by a qualified healthcare practitioner.
To discuss your condition, please contact a health practitioner or reach us directly

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