What is the morning-after pill and how does it work?

Bottom lineThe morning-after pill is emergency contraception taken after unprotected sex that works mainly by delaying or preventing ovulation; levonorgestrel (Plan B) works best within 72 hours and ulipristal (ellaOne) up to 120 hours, and the sooner the better. It's not the abortion pill and won't end an established pregnancy; a copper IUD fitted within 5 days is the most effective option, and it may shift your next period.

The morning-after pill is emergency contraception you take after unprotected sex or a contraception failure to reduce the chance of pregnancy. It works mainly by delaying or preventing ovulation.

The two types

• Levonorgestrel (for example Plan B): most effective within 72 hours (3 days), though it can be used up to 5 days with declining effectiveness
• Ulipristal acetate (ellaOne): effective up to 120 hours (5 days) and more effective later in that window

The sooner you take it, the better it works.

How it works

It delays or stops ovulation so there's no egg to fertilize. It is not the same as the abortion pill and does not end an established pregnancy or harm a developing one.

A more effective option

A copper IUD fitted within 5 days is the most effective form of emergency contraception and provides ongoing contraception afterward.

Things to know

• It's less effective than regular contraception, so it's for emergencies, not routine use
• It may shift your next period earlier or later
• Vomiting within a couple of hours may mean you need another dose
• Higher body weight can reduce effectiveness of some pills - a copper IUD or ulipristal may be better

When to see a doctor or pharmacist

For advice on the best option, and take a pregnancy test if your period is more than a week late.

See can you get pregnant on your period.

Femora helps you track whether your next period shifts after emergency contraception.