How fast does Plan B start working?

Onset of action is the time from taking Plan B (Levonorgestrel) to its first noticeable effect. For users planning around the dose — whether for an event, a daily routine or an acute symptom — knowing the typical onset window for Plan B at 1.5mg is useful, as is knowing what shifts that window earlier or later.

Typical onset for Plan B

For oral tablet containing Levonorgestrel, the first effect usually appears between 30 minutes and 2 hours after dosing in most adults. Peak effect arrives later, often after several hours. The exact window depends on the formulation, the person's metabolism and what was eaten around the time of dosing.

What slows or speeds onset

Onset is faster on an empty stomach and slower with a heavy fatty meal. Smoking, age and certain co-administered medications can also shift onset. According to the prescribing information for Levonorgestrel, the standard 1.5mg dose should not be re-dosed simply because the effect feels slow — re-dosing inside the same window stacks plasma concentrations and increases side-effect risk.

Frequently asked questions

How long does Plan B take to work? ▾

Most users feel the first effect of Plan B between 30 minutes and 2 hours after dosing at the standard 1.5mg. Empty stomach speeds onset; heavy meals delay it. Peak effect typically lands later than first onset.

Why isn't Plan B working fast enough? ▾

Slow onset is usually because of recent food, alcohol, individual metabolism or simply impatience — many users underestimate how long the first window is. Re-dosing on your own is not recommended; if onset is consistently absent, consult the prescriber rather than doubling up.

More on Plan B

The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.