It can cause anxiety when your menstrual cycle doesn’t behave as you expect. Take a look at some of the common concerns about how taking the morning-after pill affects your menstrual cycle. In this article, you will learn about common side effects of taking the morning-after pill, when you need to take a pregnancy test, and what can cause inaccurate test results.

Can Plan B make your period late?

You may experience changes to your menstrual cycle (including having a delayed period) because of higher levels of hormones in your system. There are a variety of changes that can happen. You may experience lighter or heavier menstrual bleeding than you typically do. Taking the morning-after pill may change when you get your period; your next period can be earlier or later than expected. However, your period should still show up within two to seven days of its expected date. You might want to take a pregnancy test if your period is more than a week later than expected.

What else can happen when you take the morning-after pill?

Side effects from taking the morning-after pill may vary. Other than changes to the flow and timing of your menstrual period, you may experience:

• A shorter or longer menstrual period
• Spotting or irregular bleeding (bleeding between periods)
• Side effects like nausea, headache, dizziness, vomiting, or abdominal pain
• Cramps and tenderness (may be similar to what you typically experience during your period)
• Fatigue and lagging energy (especially if your menstrual flow is heavier than it usually is)

It may take a month or more for your menstrual cycle to readjust after taking the morning-after pill. Reach out to your primary care provider if bleeding lasts longer than a week or if you develop abdominal pain three to five weeks after taking the morning-after pill. It could be a sign of an ectopic pregnancy.  

Can you miss a period after taking the morning-after pill, or does it mean you’re pregnant?

In most cases, you’ll still get your period after taking the morning-after pill. Your menstrual period might be different for a cycle, however. It can show up early or late, last for a shorter or longer time, or have a lighter or heavier flow. Take a pregnancy test if your period is more than a week late or if you haven’t gotten your period within three to four weeks of taking the morning-after pill.

Can Plan B cause a false positive or false negative result on a pregnancy test?

A tiny percentage (less than 1%) of women may get a false positive pregnancy test result after taking the morning-after pill. Usually, this result is due to having detectable amounts of human chorionic gonadotropin (hCG) in your body. Factors that may contribute to the false positive test result include:

• A recent miscarriage or abortion
• A chemical pregnancy (a miscarriage that happens within five weeks of pregnancy)
• An ectopic pregnancy (your egg implants outside the uterus)
• An evaporation line (can occur if you haven’t read a pregnancy test in time) and other user errors 
• An expired pregnancy test - check the date before using one
• Certain medical conditions, including several types of cancer
• Some medications such as fertility drugs, antidepressants, and anti-anxiety treatments

You can get a false negative pregnancy test result if you take a pregnancy test too early. You won’t get accurate results from a pregnancy test if you take it within ten days of conception. You can reduce the chances of getting a false negative test result by waiting two weeks before taking a pregnancy test. 

If my periods are always irregular, when should I test for pregnancy?

The morning-after pill shouldn’t delay your period by more than a week. Of course, this may be harder to track when your period is always irregular. So, if you don’t get your period within three to four weeks after taking the morning-after pill, take a pregnancy test. You don’t need to take a pregnancy test after taking the morning-after pill if you get your next period as usual and aren’t experiencing any pregnancy symptoms. Reasons to take a pregnancy test after taking the morning-after pill include:

• Missing your next period
• Experiencing pregnancy symptoms - some of these symptoms overlap with the side effects of taking the morning-after pill, so it doesn’t necessarily mean you’re pregnant
• Needing some peace of mind (the what if’s are giving you anxiety)
  
  

Why is my menstrual cycle getting longer?

Changes to your menstrual cycle can occur for a variety of reasons. These changes are often temporary after taking the morning-after pill. Other causes of longer menstrual cycles include:

• Certain underlying health conditions like uterine fibroids
• Hormonal imbalances - may be due to hypothyroidism
• Bleeding disorders
• Your age
• Your lifestyle
  

If you are concerned about menstrual irregularities, get in touch with your primary care provider.