Emergency Contraception: Your Options and How Well They Actually Work

The three options

Levonorgestrel pills (Plan B One-Step and generic equivalents) are available over the counter, no prescription or age restriction, at most pharmacies. They work best the sooner you take them after unprotected sex, and are officially labeled for use within 72 hours, though some effect continues up to 120 hours (5 days).

Ulipristal acetate (Ella) requires a prescription, but is more effective than levonorgestrel — particularly notable in two situations: later in the 5-day window (its effectiveness holds up better than levonorgestrel's as time passes) and at a higher body weight, where levonorgestrel's effectiveness drops off more than ulipristal's does.

The copper IUD (Paragard) is the single most effective form of emergency contraception that exists — over 99% effective, and unlike the pills, it still works even if ovulation has already happened, since it primarily works by preventing fertilization and implantation rather than delaying ovulation. It requires a same-day clinician visit for insertion, which is the main access barrier, but it then keeps working as regular contraception for up to 10-12 years if you choose to keep it in.

How effective each one actually is

The copper IUD is the clear effectiveness leader (over 99%), and its effectiveness doesn't decline with body weight or with time within the window the way the pills' does. Between the two pills, ulipristal (Ella) is generally more effective than levonorgestrel, especially the later you are in the 5-day window or at a higher BMI — some data suggest levonorgestrel's effectiveness drops meaningfully at a BMI over 25-30, while ulipristal's holds up better, though neither pill is as reliably effective at a higher body weight as the copper IUD.

How they actually work — and what they don't do

All three options work primarily by delaying or preventing ovulation (the copper IUD additionally affects fertilization and implantation). None of them will disrupt an already-implanted pregnancy — if ovulation has already happened and fertilization occurred, the pills specifically won't work, which is part of why timing matters so much and why the copper IUD is the more reliable backup later in your cycle. They are not the same as, and do not cause, a medication abortion.

Practical things worth knowing

None of these protect against STIs — that's a separate conversation if the unprotected sex was also a possible exposure. Nausea and a temporarily irregular next period (earlier, later, heavier, or lighter than usual) are common and not a sign anything went wrong. It's safe to use emergency contraception more than once if you need to, but it's meaningfully less effective than a regular ongoing method used consistently, so if you're finding yourself reaching for it repeatedly, that's worth a conversation about a regular method that fits your life better.