Finding oneself needing emergency (post-coital) contraception in an unexpected situation is something we encounter not rarely in the clinic. However, the time within which it can be taken differs by type of drug, and the mechanism of action also differs, so surprisingly few people know exactly "by when, which drug, and how to take it." Especially when the menstrual cycle is irregular, it is hard to gauge the time of ovulation, so the response can be delayed. In this article, I have organized the types of emergency contraceptive pills, the timing of use, the mechanism of action, and the changes and precautions that commonly appear after taking it, centered on the questions frequently received in the clinic.
In what situations is emergency contraception considered
Emergency contraception is a method considered after intercourse in which contraception was not used or was insufficient, to lower the chance of an unwanted pregnancy. Cases such as a condom tearing or slipping off, missing the regular pill for several days, or intercourse occurring without contraception fall under this.
Those with a regular menstrual cycle know roughly their ovulation day, making it easier to gauge the risky period. However, even with a regular cycle, the ovulation day can shift back and forth depending on condition or stress, so it is hard to conclude that the chance of pregnancy is entirely absent even on a day thought to be safe. For those with an irregular cycle, predicting the timing of ovulation is even trickier, so it is easy to miss the window for response.
In the clinic, those who usually record their own menstrual cycle tend to judge the risky period quickly and come in at an appropriate time.
If your cycle is erratic, it helps to grasp the pattern of your own cycle through regular check-ups. If you are considering which contraception suits you, you may also refer to a consultation on contraception concerns.
How does emergency contraception work
The core action of emergency contraception is blocking or delaying ovulation. The World Health Organization (WHO 2021) and the International Federation of Gynecology and Obstetrics (FIGO) explain that when emergency contraception is taken before ovulation, it suppresses the secretion of luteinizing hormone, thereby delaying follicular maturation and ovulation.
There is an important point here. According to the WHO and FIGO, emergency contraception is not a drug that terminates an already established pregnancy or affects an implanted embryo. That is, it is not a drug that ends a pregnancy, but a drug that delays ovulation before a pregnancy is established and thereby prevents fertilization. If ovulation has already occurred and fertilization has taken place, it is no longer a stage that the drug can block.
In the past, the explanation that it lowers the implantation rate by changing the uterine lining was common, but in recent evidence it is being organized that the main mechanism of emergency contraception is delaying ovulation, and that the effect of blocking implantation itself is not clear. For this reason, it is emphasized that the effect is higher the sooner it is taken before ovulation. If you are curious about the mechanism, How to choose emergency contraception wisely within 5 days covers it in more detail.
How do the types and timing of use differ
Emergency contraceptives are all prescription drugs and require a prescription after a hospital visit. Since the timing of use and the effect differ by ingredient, the choice is made to fit the situation during the visit. There are mainly the following two classes.
| Category | Levonorgestrel class | Ulipristal acetate class |
|---|---|---|
| Action | Delays ovulation by slowing the pre-ovulatory rise of luteinizing hormone | Binds to progesterone receptors to suppress and delay ovulation |
| Recommended timing | Within 72 hours after intercourse | Within 120 hours (5 days) after intercourse |
| Features | A relatively long-used ingredient | Activity reported even at a late point and near the time of ovulation |
Levonorgestrel is a relatively long-used ingredient, and use within 72 hours after intercourse is recommended. Ulipristal acetate can be taken up to a later point, within 120 hours, and the UK Faculty of Sexual and Reproductive Healthcare (FSRH 2023) explains that activity is reported even in situations where some time has passed or near the time of impending ovulation.
Both classes share a common principle. The sooner the better. Since the effect of the same drug declines as time is delayed, it is desirable to take it at as early a point as possible, even within the recommended time. Which ingredient suits your situation is safest to judge through a medical visit.
What changes can appear after taking it
Because emergency contraception works by temporarily raising the body's hormone levels, several changes may appear after taking it. There are individual differences, and most are temporary.
- Nausea/vomiting: Nausea or vomiting may occur. It may feel worse if taken on an empty stomach.
- Irregular bleeding: A small amount of bleeding may appear at a time different from what was expected.
- Change in menstrual cycle: Due to the change in hormone levels, the next period may come a few days earlier or later.
- Fatigue/headache/dizziness: These symptoms may accompany, and if the headache is severe, taking an ordinary painkiller is fine.
In particular, if you vomit within 3 hours of taking it, there is a possibility that the drug was not sufficiently absorbed, and re-taking may be necessary. In this case, rather than judging on your own, it is safer to inquire at the prescribing hospital for guidance.
If you are worried about symptoms after taking emergency contraception, get a consultationWhat precautions must be observed after taking it
Taking emergency contraception does not mean that all subsequent intercourse is protected. This is also the part most frequently emphasized in the clinic. Please be sure to remember the items below after taking it.
- Emergency contraception does not guarantee 100% contraceptive efficacy. Even if taken, the possibility of pregnancy does not entirely disappear.
- Within one menstrual cycle, a single dose is recommended. Taking it two or more times in the same cycle makes it hard to expect sufficient contraceptive efficacy.
- There is no contraceptive effect for intercourse that takes place after taking it. Therefore, until the next period begins, you must use another contraceptive method such as a condom together.
- From the start of the next period, it is good to get a consultation on steady contraceptive methods such as the regular oral contraceptive pill or the intrauterine device (Mirena).
Frequent use of emergency contraception can burden hormonal balance, so if the situation recurs, it is desirable to set up a regular contraception plan that suits you rather than relying on emergency response. As there are also points to consider depending on individual health status, such as oral contraceptives and the risk of blood clots, I recommend deciding together through a medical visit.
What should I do if my period is late
After taking emergency contraception, the expected period being moved earlier or later by within 3 days is a change that can commonly occur. This is because the temporary change in hormone levels affects the cycle.
However, it is not common for emergency contraception to delay the period by more than a week. Therefore, if the period does not begin even more than a week past the expected date, it is safe to do a pregnancy test. If the test is unclear or you feel anxious, it is better to confirm through an obstetric-gynecologic visit.
If irregular bleeding continues, or unusual lower-abdominal pain accompanies it, I also recommend getting a medical visit. After going through an emergency situation once, it is also meaningful to use it as an occasion to review your overall contraceptive method. Overall consultation including contraception can be received at the pregnancy and contraception clinic.
Emergency contraception is, literally, an "emergency" means. Taken with the correct timing and method, it helps, but it is hard for it to replace steady, everyday contraception. If you are pondering which contraception suits you, we will find the direction together in the clinic.
Written by: Lee Dong-hee Director · Obstetrics and Gynecology Specialist · See physician profile
First published December 14, 2023 · Last reviewed May 30, 2026
References: World Health Organization (2021), FSRH Clinical Guideline Emergency Contraception (2023), ACOG Practice Bulletin Emergency Contraception (2015), FIGO Mechanism of Action of Emergency Contraception
This article is intended to provide general health information and does not replace individual diagnosis or treatment. If you have symptoms, please consult through a medical visit.