In a 2021 study, researchers asked more than 500 people a simple question: How does the morning-after pill prevent pregnancy? Surprisingly, about 60% got it wrong.

Considering how widely emergency contraception is used, that’s… not great.

Part of the confusion comes from the name itself. The phrase “morning-after pill” makes it sound like something that works after pregnancy begins. But that’s not how it works at all. These pills actually work earlier in the process, before pregnancy even starts, by delaying or preventing ovulation.

This fascinating animated explainer breaks down the science behind it. Each month, the body prepares an egg for release, triggered by a surge of luteinizing hormone (LH). If that egg gets fertilized within about 24 hours, pregnancy can occur.

Emergency contraceptive pills interrupt that timeline.

One type, commonly known as Plan B, uses levonorgestrel, a hormone that interferes with the LH surge, meaning no ovulation, no egg to fertilize. Another pill uses ulipristal acetate, which blocks progesterone receptors and can delay ovulation even if the hormone surge has already started.

The big takeaway? You don’t actually have to wait until the morning after. These pills work best the sooner they’re taken, but they can still help up to 3–5 days after sex.

Science: clearing up awkward misunderstandings since forever.