MORNING AFTER PILL: HOW TO TAKE IT, EFFECTS AND EFFECTIVENESS - MEDICINE - 2025

The morning-after pill appeared on the market just over 20 years ago, and has become the emergency lifeline for hundreds of women who weren't ready to get pregnant. The vast majority of these pills are made up of progesterone, a fundamental hormone in inhibiting pregnancy.

Regardless of whether it was due to a broken condom, a night out they weren't prepared for, or even rape, the morning-after pill is responsible for preventing a good number of unwanted pregnancies.

Although many people consider that it is a pill that induces abortion, the truth is its mechanism of action has nothing to do with it; in fact, using the morning-after pill avoids unwanted pregnancies that could ultimately lead to induced abortions.

Mechanism of action

The mechanism of action varies depending on the composition of the morning after pills. However, considering that currently most of these pills (also known as emergency contraceptives) are composed only of progesterone (or some homologous progestin), this mechanism of action will be described.

It is important to clarify that in some countries there may be emergency contraceptive pills with another composition whose mechanism of action is not the one described below.

How do progesterone pills work?

During the menstrual cycle there are a series of hormonal changes that first induce the maturation of the ovules (follicular phase) and later the release of an ovum to be fertilized (ovulation).

In the first stage the predominant hormone is estrogen, while in the ovulation phase the critical hormone is LH (Luteinizing Hormone), which induces a kind of erosion in the ovary wall that is in contact with the ovum in order to to allow it to break free.

Once the egg is released from the ovarian follicle, it turns into the corpus luteum which begins to secrete large amounts of progesterone, which in turn inhibits LH secretion. And that is precisely where emergency contraceptive pills work.

After unprotected sex, when a woman takes emergency contraception, progesterone levels in her blood rise sharply (due to the pill).

This is detected by the pituitary gland (gland that secretes LH) as a sign that ovulation has already occurred, so that the natural secretion of LH in the woman's body is suppressed.

In this way, the pill "tricks" the pituitary so that the chemical signal that releases the ovum is not generated and therefore it remains "imprisoned" within the follicle where it cannot be fertilized; thus avoiding pregnancy in that menstrual cycle.

On the other hand, high doses of progestogens (usually 1.5 mg of levonorgestrel or its equivalent) cause cervical mucus to increase in viscosity, making it difficult for sperm to enter the uterus and from there to the tubes (where fertilization must occur), so this is a complementary mechanism of action.

How to use?

Since the morning-after pill inhibits ovulation, it should be taken as soon as possible after unprotected sex; in this sense, the sooner it is used, the higher the effectiveness rate.

Regarding the route of administration, this is always oral although the presentation varies from brand to brand and from country to country.

Most commonly, a 1.5 mg tablet or two 0.75 mg Levonorgestrel tablets are presented. In the first case, a single tablet should be taken once, while in the second, both can be taken together once or once every 12 hours for two doses (that is, two tablets).

How many times and how often can it be used

Since these are high-dose progestogens that somehow interfere with a woman's hormonal balance during the menstrual cycle, it is recommended that the use of emergency contraception be limited to no more than three times a year.

On the other hand, emergency contraception should never be used more than once per menstrual cycle; that is, it can be used a maximum of three times per year in separate cycles.

Side effects

Most of the side effects of contraceptive pills are mild and can be tolerated without major inconvenience, spontaneously subsiding between 24 and 72 hours after administration.

Among the most common side effects are:

-Gastrointestinal intolerance (nausea and sometimes dyspepsia).

-Feeling of fatigue.

-Drowsiness.

-Mastalgia (pain in the breasts).

-Increase in the volume of menstrual bleeding and irregularity in one or two cycles after the administration of the treatment.

Effectiveness

Studies report that if emergency contraception is used within the first 24 hours after unprotected intercourse, the success rate is between 90 and 95%, decreasing approximately 5 to 10% for every additional 12 hours until maximum time of 72 hours.

That is, emergency contraception can be used up to the third day after unprotected sex.

However, some studies indicate that protective effects against unwanted pregnancy could be seen for up to 5 days, although success rates are markedly lower.

From the above, it can be concluded that the term morning-after pill is somewhat imprecise, since it is not essential to take the pill exactly the day after (as with first-generation emergency contraceptives) because there is a window of 72 hours to do it.

Precautions

Emergency contraceptive pills should not be used as a regular contraceptive method, for this there are other methods specifically designed to be effective when used routinely.

On the other hand, it is important to note that emergency contraceptive pills do not have the same effect if they are administered before intercourse and not once ovulation has occurred. That is, if the woman had already ovulated when she had sexual intercourse, it does not matter if she took emergency contraception immediately, its effect will be zero.

Finally, it must be remembered that emergency contraception does not protect against sexually transmitted diseases, so in random sexual encounters it is better to use barrier methods.

References

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7. Trussell, J., Stewart, F., Guest, F., & Hatcher, RA (1992). Emergency contraceptive pills: a simple proposal to reduce unintended pregnancies. Family planning perspectives, 24 (6), 269-273.
8. Rodrigues, I., Grou, F., & Joly, J. (2001). Effectiveness of emergency contraceptive pills between 72 and 120 hours after unprotected sexual intercourse. American Journal of Obstetrics & Gynecology, 184 (4), 531-537.