Can The Morning After Pill Affect Your Period?
The morning after pill can affect your period in a few different ways. This includes making it early or slightly late, or lighter bleeding. The morning after pill contains an active ingredient that acts like a hormone similar to the one your body naturally makes.
Any medication that affects your hormones can impact your period. This includes birth control pills and hormone replacement therapy.
The morning after pill works best if you take it within 24 hours of having unprotected sex. Unprotected sex means having sex without a condom. Unprotected sex can also happen when your regular method of contraception fails, such as the condom breaking or if you forget to take your birth control pill.
The morning after pill does not protect you against sexually transmitted infections (STIs). Only condoms can protect you against STIs.
Does the morning after pill delay your period?
The morning after pill can delay your period or even make it come early. It’ll usually only delay your period by a few days. If you still have not got your period after 7 days from when you expect to get it, do a pregnancy test.
There are other factors that can change when your period comes. Your period might be delayed if you:
- normally have irregular cycles
- are stressed
- take other medications
- have lost weight recently
- have certain health conditions like thyroid disorders, diabetes or polycystic ovarian syndrome (PCOS)
You might not be pregnant if your period is slightly late, but it’s understandable if this concerns you. Most pregnancy tests will not be sensitive to a positive reading until 21 days after you’ve had sex. If you’re concerned that you might be pregnant, speak to your doctor.
Why does the morning after pill affect your period?
The morning after pill affects your period as it prevents ovulation. Ovulation occurs when your ovaries release an egg to get ready for fertilisation by sperm. Ovulation is a stage that normally happens around the middle of your menstrual cycle.
Your menstrual cycle is made up of four main stages: menstruation, the follicular phase, ovulation and the luteal phase. If something, such as the morning after pill, affects one stage of the cycle it can impact a later phase.
There are 2 types of emergency contraceptive pills: Levonelle and EllaOne. Levonelle contains the active ingredient levonorgestrel, a type of progestin. Progestins are synthetic hormones that mimic the natural hormone progesterone.
EllaOne contains ulipristal acetate, an ingredient that affects the progesterone receptor. Both levonorgestrel and ulipristal acetate can affect the hormones in your menstrual cycle.
Changes to your period can be a common side effect of the morning after pill. These include making it early, late or even lighter in bleeding.
Temporarily delaying or preventing ovulation can have a knock on effect of delaying your period. A late period does not mean you’re pregnant, but that your regular cycle is delayed by a few days. It should go back to normal the following cycle.
How late can your period be after taking the morning after pill?
Your period can be up to a week late after taking the morning after pill. In some cases, it can be more than a week. If you know where you are in your menstrual cycle, take a pregnancy test once your period is more than a week late. If you’re unsure, you should wait around 21 days (3 weeks) after unprotected sex before taking a test.
You can speak to your pharmacist or doctor if you’re unsure about how long you should wait before taking a pregnancy test.
How to know if emergency contraception worked
The only way to know if emergency contraception has worked is when you get your next period. Unfortunately, this does mean it’s a bit of a waiting game to know whether you’re pregnant or not.
If you’ve taken the morning after pill at the right time, within 24 hours of unprotected sex, there’s a 95 to 99% chance that the emergency contraception has worked. The later you take the morning after pill, the less effective it becomes at preventing pregnancy. Levonelle (levonorgestrel) can work up to 72 hours and EllaOne up to 120 hours after unprotected sex.
The morning after pill will only work if you take it before ovulation. You can tell you might be ovulating if you work out what is roughly 10 to 16 days before your period. You may also notice the signs of ovulation, such as changes in your cervical mucus or a small increase in your overall body temperature. However, it is difficult to track when you might ovulate.
Another form of emergency contraception is the copper IUD (intrauterine device). This is a small device that is fitted inside your uterus. The copper IUD can be left in your uterus to be used as regular contraception. For emergency contraception, the copper IUD needs to be fitted within 5 days of having unprotected sex.
If you’ve taken any emergency contraception after ovulation, it will not work. Look out for the signs of pregnancy, including nausea, vomiting, abdominal pain and breast tenderness. You may bleed a little in the early stages of your pregnancy, which might be confusing if you’re waiting for your period. If this happens, do a pregnancy test or speak to your doctor.
Dr Babak Ashrafi Clinical Lead for Service Expansion
Babak studied medicine at King’s College London and graduated in 2003, having also gained a bachelor’s degree in Physiology during his time there. He completed his general practice (GP) training in East London, where he worked for a number of years as a partner at a large inner-city GP practice. He completed the Royal College of GPs membership exam in 2007.Meet our doctors
Last reviewed: 23 May 2022
Can The Morning After Pill Delay Your Period? Ask Ella (EllaOne) [accessed April 2022]
How Late Can Your Period Be After Taking Plan B? (Healthline) [Dec 2020] [accessed April 2022]
You might need emergency contraception if you’ve recently had unprotected sex and want to reduce your risk of getting pregnant. ZAVA offers a morning after pill service, which includes a variety of options.