The morning after pill is an emergency backup option for preventing pregnancy. It can be used after unprotected sex or contraceptive failure and is a crucial option for preventing pregnancy.
In this guide, we will explain how the morning after pill works, the possible side effects, and what to do if your period is delayed.
Taking the morning after pill can bring a lot of questions, especially around how it might affect your menstrual cycle. This guide is here to help you understand what to expect and when you might need to seek further advice.
How the morning after pill works
The morning after pill is an emergency contraceptive that primarily works by delaying ovulation. This means it stops the egg from being released from the ovary, which in turn prevents pregnancy. There are two main types of morning after pills available:
- Levonorgestrel-based pills (e.g., Plan B): Most effective when taken within 12 hours of unprotected sex but can be taken up to 72 hours after. Approximately 97% effective at preventing pregnancy [1].
- Ulipristal acetate-based pills (e.g., Ella): Most effective when taken within 24 hours of unprotected sex but can be taken up to 120 hours (5 days) after unprotected sex. Approximately 98% effective at preventing pregnancy [2].
Does the morning after pill delay periods?
Yes, the morning after pill can delay your period. The hormonal changes induced by the pill can affect the menstrual cycle. After taking the morning after pill, your period may start a little earlier or later than expected. Some people may also experience a lighter or heavier bleed than usual [3].
How will taking the morning after pill affect my next period?
The hormones in the morning after pill delay ovulation and can temporarily disrupt your usual cycle. While your next period may arrive on time, it’s also common for it to be slightly early or late. Some may experience spotting, and the flow could be heavier or lighter than usual.
When should I be concerned about a late period?
Although the morning after pill is highly effective, it isn’t 100% guaranteed to prevent pregnancy. If your period is 5–7 days late, consider taking a pregnancy test. Alternatively, if it’s been at least 21 days since unprotected sex and you’re concerned, a pregnancy test can offer clarity.
If your bleeding is significantly different from normal, or you experience unusual lower abdominal pain, it’s wise to speak to a doctor. Severe lower abdominal pain should be assessed in A&E. Other factors like stress, significant changes in weight or exercise, and conditions such as polycystic ovary syndrome can also affect period timing.
How long does it take for periods to return to normal after taking the morning after pill?
The morning after pill generally only affects the first period following its use. Your next cycle and future periods should return to normal.
How much delay in periods after taking the contraceptive pill?
After taking the morning after pill, it is common for your period to be delayed. The hormonal changes induced by the pill can affect the menstrual cycle, leading to a late period after taking the morning after pill. The maximum delay in periods after taking the morning after pill is usually around a week, though this can vary. If your period is delayed by more than seven days, it's advisable to take a pregnancy test to rule out pregnancy [5].
It's important to note that other factors can also cause delayed periods, such as stress, changes in weight, or underlying medical conditions like polycystic ovary syndrome (PCOS) [6].
Other changes to your period
Besides a delay, the morning after pill can also cause other changes to your period. The flow might be heavier or lighter than normal, and some may experience spotting or bleeding after taking the morning after pill. These changes are due to the hormonal disruption caused by the pill and are generally nothing to worry about [7].
What should I do if my period is late after taking the morning after pill?
If your period is late after taking the morning after pill, it’s natural to be concerned. Here’s what you should do:
- Take a pregnancy test: If your period is more than a week late, it’s wise to take a pregnancy test to rule out pregnancy [5].
- Monitor your symptoms: Pay attention to any unusual symptoms like severe abdominal pain or heavy bleeding [7].
- Consult a healthcare provider: If your period is more than two weeks late or if you have other concerns, it's best to speak with a doctor [8].
When should I see a doctor after taking the morning after pill?
- To discuss a more reliable long-term contraception method.
- If your period doesn’t return and your pregnancy test is negative.
- If your normal cycles don’t resume as expected.
- For severe lower abdominal pain or significantly heavy bleeding, seek help in an urgent care setting.
- If you're concerned about possible STI exposure, a sexual health screen is advised.
How HealthHero can help
If you're worried about a delayed period after taking the morning after pill, or if you have any other concerns, HealthHero is here to help. Our online GP service allows you to speak with a doctor who can provide advice and reassurance. Whether you need help understanding what’s normal or unsure about the next steps, we’re here to support you.
The morning after pill can delay your period, but usually by no more than a week. If your period is delayed longer than this or if you have other concerns, it's important to seek medical advice. Emergency contraception is safe and effective, but it's always best to know what to expect.
