Levonorgestrel Emergency Contraception Works Well — Even if Taken Before Sex

Precoital EC can be more effective

By Melinda Young

A new study using a mathematical model finds that an oral dose of 1.5 mg levonorgestrel emergency contraceptive (LNG-EC) is safe and largely effective both when taken shortly before sexual intercourse and shortly after — so long as the woman is not ovulating.¹

LNG-EC is sold under the name Plan B One-Step, and it consists of a single round tablet with 1.5 mg of levonorgestrel. It has a marking of G00 on one side.

Both the World Health Organization and the U.S. Centers for Disease Control and Prevention recommend that women have an advanced supply of emergency contraception (EC) on hand to minimize delays, says Douglas J. Taylor, PhD, senior advisor to quantitative sciences in the product development and introduction department of FHI 360 in Durham, NC.

Research shows that EC works best if someone takes it soon after having sex, within an hour.

“If it’s taken within an hour or two after sex, it has 91% effectiveness — depending on whether the person has ovulated or not,” Taylor says.

“It’s not going to work if it’s taken on the day of ovulation or the day after,” he adds.

Most people who use EC may delay taking it — even when they have a pill on hand. If they have to drive to a drug store to find a box, it could be a day or longer before they take the pill.

Taylor and co-investigators examined nine studies and calculated the effectiveness of taking levonorgestrel EC based on real-life data of people taking the pill up to 72 hours after sex. The population-average maximum attainable effectiveness levels ranged from 49% to 67% when accounting for postcoital delays.¹

“The average delay was 24 hours,” Taylor notes. “The longer you wait, the less likely you take it before ovulation and the less likely it would work.”

There is a way for people who anticipate having unprotected sexual intercourse to use EC without a delay, and that is by taking the pill three hours or less before having sex.

The question is whether this works well in preventing pregnancy, and the new study finds that it does work well. It does not work as well as taking EC immediately after intercourse, but it works better than the real-life practice of taking EC many hours afterward.

Based on the investigators’ modeling, precoital use of LNG-EC has population-average maximum attainable effectiveness levels that range from 70% to 81%. The model estimated effectiveness based on half of subjects taking LNG-EC within three hours before sex.¹

“Our message is you don’t want to delay. If you had unprotected sex, to avoid pregnancy, take it as soon as you can after or before unprotected sex,” Taylor says.

Precoital LNG-EC is not a practical solution for everyone because many people do not know they need EC until after they have sex and something happens, such as a broken condom, he adds.

“So, many people have to go out to get it, and that delay will reduce effectiveness for people,” Taylor explains. “If they had it in advance, it can help if a person’s partner doesn’t use condoms or if there is a problem with the condom.”

Reproductive healthcare clinicians need to let patients know that it is important to have LNG-EC in advance, especially if they occasionally have unprotected sex. And they can safely and effectively take the medication three hours or less before they have sex.

Clinicians also need to remind patients that LNG-EC is not an abortifacient, despite misinformation online and that is being spread by anti-abortion groups and politicians.

“It’s not an abortifacient,” Taylor says.

The Food and Drug Administration’s labeling clearly states that “Plan B One-Step is not effective in terminating an existing pregnancy.”

It works by delaying ovulation, not by ending a pregnancy, Taylor says.

“That’s what the evidence says is the case,” he adds.

REFERENCES

1. Taylor DJ, Kapp N, Steiner MJ. Maximizing the effectiveness of 1.5 mg levonorgestrel for emergency contraception: The case for precoital use. Contracept X 2024;6:100107.
2. U.S. Food and Drug Administration. Plan B One-Step: Highlights of prescribing information. https://www.accessdata.fda.gov/drugsatfda_docs/label/2009/021998lbl.pdf