Yes. For the most common morning-after pill (levonorgestrel, sold as Plan B, I-pill, and similar brands), effectiveness seems to drop as body weight goes up. Research suggests it may not work as reliably above a certain weight. This isn't true of every emergency contraception option. So body weight should affect which one you choose — it is not a reason to skip emergency contraception.

What the evidence actually shows

  • Levonorgestrel (the most common morning-after pill) — studies indicate its effectiveness starts to decline at higher body weights, and some data suggests it may be substantially less reliable in that range; it isn't that it "stops working," but that the odds of it failing go up
  • Ulipristal acetate (a prescription-only option in some countries) — appears to hold its effectiveness across a wider weight range than levonorgestrel, though it too may become less reliable at very high body weights
  • The copper IUD — the most effective emergency contraception option overall, and its effectiveness doesn't depend on body weight, because it works mechanically rather than hormonally
  • Global guidance on an exact weight or BMI "cutoff" isn't settled — different studies and regulators haven't agreed on one precise number, so talk to a doctor rather than checking yourself against a chart

What this means in practice

If your body weight is on the higher side, the concern with levonorgestrel is how well it works at your weight, not how soon you took it. (Taking it as soon as possible still matters for everyone.) There are two other options. Ask a doctor or pharmacist whether ulipristal acetate is available and right for you. Or consider a copper IUD inserted within 5 days, which is the most effective option and is not affected by body weight.

Emergency contraception is still worth taking at any body weight — it lowers pregnancy risk compared to taking nothing. But if you can get one, a copper IUD or ulipristal acetate is a more reliable choice at higher body weights than a second levonorgestrel dose.

Frequently asked

Should I just take two morning-after pills if I weigh more?

No — doubling the dose is not proven to make it work better and can increase side effects like nausea without good evidence that it improves protection. If you're concerned about effectiveness at your body weight, ask about ulipristal acetate or a copper IUD instead.

Is there an exact weight cutoff where levonorgestrel stops working?

There isn't a single agreed number — studies point to reduced effectiveness at higher body weights, but regulators and researchers haven't settled on one universal cutoff. This is best discussed directly with a doctor or pharmacist who can weigh your specific situation rather than relying on a fixed chart.

How soon does emergency contraception need to be taken?

Sooner is always better. Levonorgestrel works best within 72 hours, though it is sometimes used a bit later with less effect. A copper IUD can be inserted up to 5 days after unprotected sex and works well throughout that time. If several days have already passed, a copper IUD is the option to ask about first.

Does this affect regular birth control pills too?

This specific weight-related effectiveness concern is best established for emergency contraception, particularly levonorgestrel. If you have concerns about your regular contraception and body weight, talk to your doctor separately about the method that suits you best.