Explainer: What is the morning-after pill and how does it work?

April 16, 2014 by Beverley Vollenhoven, Monash University
The morning-after pill is available in Australian pharmacies without prescription. Credit: Shutterstock

Condoms break, contraceptive pills are missed and in the throes of passion, contraception might be overlooked. So from time to time, a woman may need emergency contraception, known as the morning-after pill.

The morning-after is available in Australian pharmacies without prescription. The pharmacist may ask you about what contraception you are using and what other medication you're taking. But you will not be required to show identification.

The most commonly used morning-after pill available in Australia is Postinor. This pill contains the hormone progestogen and can be taken as a single dose (1.5 mg) or as two doses (0.75 mg, 12 hours apart). Both are equally as effective.

How does it work?

The chance of is greatest in the two days leading up to and including ovulation. An egg lives for 24 hours and sperm can live for up to three to five days, therefore conception can occur several days after sex.

The morning-after pill works by delaying the increase in the hormone that starts ovulation, the release of an egg. By delaying or stopping the egg from being released, the sperm can't reach the egg and pregnancy can't occur.

The morning-after pill therefore needs to be taken before the hormone surge occurs; its effectiveness decreases the closer it's given to and it is not effective if given after fertilisation has occurred.

Copper intrauterine devices (IUDs) are an alternative method of contraception and can be inserted up to five days after unprotected sex. Depending on the type, IUDs protect against pregnancy for five or ten years.

In the past, the morning-after pill has been thought to prevent implantation and has therefore been termed an abortifacient. This is categorically incorrect.

Implantation can only occur if an embryo is created when a sperm enters an egg. If fertilisation has not occurred then an embryo has not been created and therefore the morning-after pill is not preventing implantation.

Pharmacists should therefore have no hesitation in dispensing the morning-after pill, no matter what their on abortion.

How effective is it?

The earlier the morning-after pill is taken after unprotected sex, the greater the success in preventing pregnancy. Ideally the pill should be taken within 72 hours, in which case the rate of efficacy is around 85%.

If taken after 72 hours, the effectiveness reduces. At 120 hours, the risk of pregnancy is five times greater than if taken within 24 hours of unprotected sex.

After taking the morning-after pill, women should use a barrier method of contraception, such as condoms, for the remainder of their cycle. The morning-after pill might delay the next period. But if it's more than 21 days late, it's best to take a pregnancy test.

Recent research has shown that as a woman's weight increases, the effectiveness of the morning-after pill decreases. Obese women (with a body mass index of 30 or above) who take the morning-after pill are four times as likely as their healthy weight counterparts to become pregnant.

Being obese doesn't preclude women from taking the morning-after pill but it's important to note it reduces its efficacy. In such cases, women may choose to have a copper IUD inserted instead.

There are medicines that interact with the morning-after pill and potentially make it less effective: some anti-epilepsy medicines, St John's Wort and drugs for tuberculosis and HIV. These medicines speed up the breakdown of the morning-after pill in the body.

It's important to tell your pharmacists about other medicines you're taking in case there is a drug interaction. In such cases, your pharmacist may recommended you take a higher dose of Postinor.

Is it safe?

There have been no deaths or reports of serious problems after taking the morning-after pill and it's also safe to use while breastfeeding. If pregnancy does occur, there is no evidence the drug will cause any harm to the fetus.

It has never been shown that accessibility to the morning-after pill leads to an increase in use, an increase in or to a decrease in the use of ongoing contraception.

It's important that all women – especially teenagers – are well informed on the availability of the . This information should be given in an impartial manner without judgement.

Explore further: Morning-after pill may not work in heavier women

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