Can Emergency Contraceptive Pills Delay Your Period?

Can emergency contraceptive pills cause a delay in menstruation?

Hello, doctor.
I would like to ask if emergency contraceptive pills can cause a delay in my menstrual period.
My menstrual cycle is not very regular, but it averages about 24 days.
I had my last period on November 2, then again on November 23, and on December 16, I had unprotected intercourse but with withdrawal (not sure if there was any contact).
Because I was worried about pregnancy, I took emergency contraception (Ella) on December 18.
My period was supposed to arrive on December 16, but it has been delayed for 4 days and has not come yet.
What is the possibility of pregnancy? What could be the reasons for the delayed period?

SHARON, 20~29 year old female. Ask Date: 2015/12/21

Dr. Lin Wenbin reply Obstetrics and Gynecology

Consult a physician to check for hormonal imbalances in order to confirm the diagnosis.

Reply Date: 2015/12/21

More Info

Emergency contraceptive pills (ECPs), commonly known as "morning-after pills," are designed to prevent pregnancy after unprotected intercourse or contraceptive failure. They primarily work by delaying ovulation, preventing fertilization, or inhibiting implantation of a fertilized egg. However, one of the side effects of taking ECPs can be a delay in your menstrual period.

In your case, you mentioned that your menstrual cycle is not very stable but averages around 24 days. You took the emergency contraceptive pill on December 18 after having unprotected intercourse. Since your last menstrual period started on December 16, it is understandable that you are concerned about the delay in your period, which is now four days late.

It is important to note that ECPs can affect your menstrual cycle in several ways. They may cause your next period to come earlier or later than expected. In some cases, the period may be lighter or heavier than usual. The hormonal changes induced by the ECP can disrupt your regular cycle, leading to variations in timing. This is particularly relevant for individuals with irregular cycles, as the hormonal fluctuations can have a more pronounced effect.

Regarding your concern about the possibility of pregnancy, while ECPs are effective, they are not 100% guaranteed to prevent pregnancy. The effectiveness of ECPs decreases the longer you wait to take them after unprotected intercourse. Since you took the pill within a few days after the incident, the chances of preventing pregnancy are relatively high, but not absolute. If your period does not arrive within a week or so, it would be prudent to take a pregnancy test to rule out pregnancy.

In summary, the delay in your period could be attributed to the hormonal effects of the emergency contraceptive pill. It is not uncommon for ECPs to cause a delay in menstruation, especially if your cycle is already irregular. If your period does not arrive soon, consider taking a pregnancy test and consulting with a healthcare provider for further guidance. They can provide personalized advice based on your health history and current situation. Remember, it is always best to consult with a healthcare professional for any concerns regarding your reproductive health and menstrual cycle.

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