Ella Works by Hitting the Pause Button on Ovulation

Here's the one-sentence answer: Ella (Ulipristal Acetate) prevents pregnancy by blocking progesterone's signal in your body, which delays or stops the release of an egg from your ovary.

If that sounds confusing, don't worry. This guide explains exactly how Ella works in your body, using plain English and simple analogies — no medical degree required.

What Ella Does in Your Body

To understand how Ella works, it helps to know what normally happens during your menstrual cycle when you could become pregnant.

The Normal Process (Without Ella)

Each month, your body prepares to release an egg from one of your ovaries. This process is called ovulation. Here's the simplified version:

1. Your brain sends hormonal signals (including a surge of luteinizing hormone, or LH) telling an ovary to release an egg.
2. Progesterone, a key hormone, plays a role in timing this release.
3. The egg is released and travels down the fallopian tube, where it can be fertilized by sperm.
4. Sperm can survive in the reproductive tract for up to 5 days, waiting for an egg.

This is why emergency contraception has a multi-day window: sperm may already be waiting when your egg is released.

How Ella Interrupts the Process

Ella is a selective progesterone receptor modulator. Think of it this way:

Imagine progesterone is a key, and progesterone receptors in your body are locks. Normally, when progesterone (the key) fits into the lock, it triggers a series of events that lead to ovulation.

Ella acts like a fake key. It slides into the same lock (the progesterone receptor) but doesn't turn it. Instead, it blocks the real key (progesterone) from getting in. Without progesterone's signal, the chain of events that triggers ovulation gets disrupted.

The result: ovulation is delayed or prevented entirely. If no egg is released, sperm have nothing to fertilize, and pregnancy can't occur.

Why This Matters for Timing

This mechanism is what makes Ella effective even 4 or 5 days after unprotected sex. Sperm can survive up to 5 days in the reproductive tract. If Ella can delay your ovulation past the point where those sperm are still viable, pregnancy is prevented. It's a race against the clock — and Ella buys you more time by postponing the egg's release.

How Long Does Ella Take to Work?

Ella starts working quickly after you take it. The 30 mg tablet is absorbed into your bloodstream and begins binding to progesterone receptors within hours.

However, "working" in this case means delaying ovulation, not creating an immediate barrier. The medication is most effective when taken as soon as possible after unprotected sex. While it's approved for use up to 120 hours (5 days), clinical data shows that effectiveness is highest when taken sooner.

Unlike some medications where you need to wait days to see an effect, Ella's job is done once it delays or prevents the next ovulation. You won't "feel" it working — the effect is hormonal and internal.

How Long Does Ella Last in Your System?

Ulipristal Acetate has a half-life of about 32 hours, meaning it takes roughly 32 hours for half the drug to be eliminated from your body. It remains active long enough to cover the critical window around ovulation.

This is also why there's an important rule about hormonal birth control after taking Ella: you should wait at least 5 days before restarting hormonal contraception (the pill, patch, ring, etc.). Since both Ella and hormonal contraceptives act on the progesterone receptor, using them at the same time can reduce the effectiveness of both. Use condoms or another barrier method in the meantime. For more details, see our guide on Ella drug interactions.

What Makes Ella Different from Plan B?

Both Ella and Plan B (Levonorgestrel) are emergency contraceptive pills, but they work through different mechanisms:

Plan B (Levonorgestrel)

• Delivers a large dose of progestin (a synthetic form of progesterone)
• Works by flooding the system with progestin, which can suppress the LH surge and delay ovulation
• Most effective within 72 hours (3 days)
• Effectiveness drops significantly after 3 days
• Available over the counter

Ella (Ulipristal Acetate)

• Blocks progesterone from acting on its receptor (opposite approach to Plan B)
• Can delay ovulation even when the LH surge has already begun — a critical window where Plan B becomes less effective
• Maintains effectiveness up to 120 hours (5 days)
• Requires a prescription

The key difference: Plan B adds more progestin to your system, while Ella blocks progesterone from working. This is why Ella remains effective later in the fertile window — it can still delay ovulation even when the hormonal cascade is already underway.

For a full comparison of your options, see Alternatives to Ella.

The Copper IUD

It's worth mentioning the Copper IUD (Paragard) as well. It works through a completely different mechanism — copper ions create an environment that's toxic to sperm. When inserted within 5 days of unprotected sex, the Copper IUD is the most effective form of emergency contraception, and it doubles as long-term birth control for up to 10 years.

Does Ella End a Pregnancy?

No. Ella does not terminate a pregnancy. If you're already pregnant (meaning a fertilized egg has implanted), Ella will not work. It's designed to prevent pregnancy from occurring in the first place by delaying ovulation. This is an important distinction — Ella is emergency contraception, not an abortion pill.

Final Thoughts

Ella works by blocking progesterone's signal, delaying or preventing ovulation so that sperm and egg never meet. It's like hitting a pause button on your cycle at exactly the right moment. This unique mechanism is what makes Ella effective for a full 5 days — longer than any other emergency contraceptive pill.

If you need Ella, the most important thing is to act quickly. The sooner you take it, the better it works. Find a provider who can prescribe it, then use Medfinder to locate a pharmacy with Ella in stock.