Post-Coital Oral Emergency Contraception

By: Sarah Ly

Post-Coital Oral Emergency Contraception

Post-coital oral emergency contraception is used for the prevention of pregnancy after intercourse. The contraception comes in the form of pills, often collectively referred to as morning-after pills. Post-coital use of morning-after pills separates them from traditional contraception which is either a continual preventative process, such as the birth control pill, or used during intercourse, such as condoms. Oral emergency contraception is important to embryology because it represents a significant accomplishment in the human ability to manipulate the process of embryonic development and pregnancy. Though there are still many misunderstandings about the morning-after pills as a contraceptive method, the continued efforts of scientists to carry out research on emergency contraception suggests that the technology may continue to improve and grow into more widespread use.

The origin of emergency contraception can be traced back to the 1920s when scientists first showed that post-coital contraception could work in mammalian animals. Dogs and horses were brought into clinics shortly after mating and were administered small doses of extracted ovarian estrogen. The treatment prevented the animals from becoming pregnant. Veterinary physicians quickly embraced the scientific findings and began putting them into practice, creating a radical new development in contraceptive technology.

Some reports of human trials can be traced back to the 1940s, but it was not until the 1960s that physicians officially documented the first successful case of human emergency contraception. The study, from the Netherlands, documented a group of medical practitioners successfully executing the same animal-tested method of treatment performing emergency contraception on a thirteen year-old rape victim. Meanwhile, US scientists were also gathering positive findings about the role of estrogen treatments in pregnancy prevention. In 1974, Albert Yuzpe developed a specific cocktail of the hormones estrogen ethinyl estradiol and progestin. This cocktail displayed high efficacy and low side effects, and was later coined the Yuzpe Regimen. From that point on, emergency contraception became a focus for scientists who would later develop more effective variations of the treatment as well as test the efficacy and safety of emergency contraception.

In 1997 The US Food and Drug Administration (FDA) officially announced the safety and efficacy of oral emergency contraceptive pills. However, this approval only affects a physician’s right to prescribe the morning-after pills to patients for emergency contraception. In fact, not a single drug company has yet to apply for FDA approval to officially market and advertise morning-after pills for postcoital contraception.

Scientists have developed many varied hormone formulas for emergency contraceptive pills since the 1960s, which have led to a large variety of different oral contraceptive treatment courses. In the US, there are currently eighteen commercial brands of emergency contraceptive pills available to the public. These include Plan-B, Seasonale, and Ovral. The Yuzpe method remains the most commonly used hormone cocktail in pills today. The Yuzpe method is the most thoroughly studied method, and boasts a seventy-five percent rate reduction of unplanned pregnancies. It should be noted that this value does not represent the success rate of the drug, but rather, compares the difference in number of pregnancies that would be seen without treatment versus with treatment. For example, within a finite population of women who have unprotected sex, a given proportion of them would become pregnant. If they all received the morning-after pill, the number of pregnant woman would be only one-fourth of the original statistic.

The title of the morning-after pill is misleading in several ways. First, the morning-after pill encompasses an entire course of treatment which generally involves multiple pills taken in two dosages, rather than a single pill taken just once. The prescribed dosages can be as large as twenty pills, and are consumed by the individual twelve hours apart from each other. Additionally, in contrast to what the phrase “morning-after” would suggest, women do not have to wait until the morning subsequent to unprotected intercourse to take the pill. Also, the effectiveness of the pill does not expire after one day. In fact, the morning-after pill is intended to be effective if taken up to seventy-two hours after intercourse. Scientific studies illustrate the fact that this established time frame does not represent a maximum time for the drug’s efficacy, as treatments induced as late as 120 hours after unprotected sex have been successful in preventing pregnancy. These results underlie the fact that the prescribed limitations of the pill may not be as absolute as they seem and that further studies could change the official treatment guidelines of the morning-after pill.

Although the exact mechanism of contraception enacted by emergency contraceptive pills has not been concretely established, different studies support several plausible physiological explanations for the drug’s effectiveness. For example, much research has shown that ingestion of the morning-after pill can stall ovulation, which corresponds to the fact that the morning-after pill is most effective when taken before ovulation. Other researchers observe that the morning-after pill induces changes in the endometrium, or inner lining of the uterus that influences a woman’s ability to conceive during, and after, the course of treatment, though these observations have been contradicted by other scientists. Some other ideas regarding the mechanism of pregnancy prevention include changes to the cervical mucus, intervention of embryo transport, and direct fertilization interference.

Although the mechanism has not been found, numerous scientific studies attest to the safety of the morning-after pill. But like any drug, there are documented side effects. The most prominent warning that accompanies emergency contraception is that it should not be administered after a woman becomes pregnant. However, even so, studies reveal no evidence of birth defects in children born to mothers who took the morning-after pill while unaware that they were already pregnant. Common side effects related to emergency contraceptive pills include nausea, dizziness, abdominal pain, and fatigue.

Despite its long history of being used and the many studies that confirm its safety, oral emergency contraception remains attached to multiple stigmas. Some opponents of morning-after pills suggest that post-coital use of the pills encourages unsafe sexual practices. Additionally, surveys often find that many individuals equate the morning-after pill to abortion, though the pill prevents the occurrence of pregnancy rather than interrupting it during the process of embryogenesis. Oral emergency contraceptives are an important milestone in the history of embryology and fertility because their use symbolizes the human desire to manipulate and predict pregnancy.


  1. Ellerston, Charlotte. “History and Efficacy of Emergency Contraception: Beyond Coca-Cola,” International Family Planning Perspectives 22 (1996): 52–56.
  2. Grimes, David. “Emergency Contraception,” Annals of Internal Medicine 137 (2002): 18–189.
  3. Trussel, James. “The Role of Emergency Contraception,” American Journal of Obstetrics and Gynecology 190 (2004): 30–38.


How to cite

Ly, Sarah, "Post-Coital Oral Emergency Contraception". Embryo Project Encyclopedia ( ). ISSN: 1940-5030


Arizona State University. School of Life Sciences. Center for Biology and Society. Embryo Project Encyclopedia.

Last modified

Monday, September 11, 2023 - 10:58

Share this page