Evidence checked as of October 2026. Written by The Wellness Team.
How long does the morning-after pill work?
There are two pills. Levonorgestrel, the older and cheaper one, is licensed for up to 72 hours after unprotected sex and works best within the first 24 hours; its effectiveness falls with every day that passes. Ulipristal acetate works for up to 120 hours, five days, and holds its effectiveness better across that window. Neither protects against sex that happens later in the same cycle.
The third option is the most effective of all: the copper intrauterine device, fitted within five days, prevents more than 99% of expected pregnancies and then works as ongoing contraception for years. It needs a fitting appointment, which is why the pills exist, but anyone within the five-day window should be told it is an option.
Which type is most effective?
Per the Faculty of Sexual and Reproductive Healthcare, the copper IUD is the most effective emergency contraception, followed by ulipristal, then levonorgestrel. The differences are not trivial in the 72 to 120 hour window, where levonorgestrel is largely spent but ulipristal and the IUD still work.
The right choice depends on timing, your weight, your other medicines, whether you want ongoing contraception, and how quickly each option can actually be obtained. That is a short conversation with a clinician, not a guess at a shelf.
Does body weight affect how well it works?
Evidence reviewed by the FSRH suggests levonorgestrel may be less effective in women over 70kg or with a BMI over 26, and ulipristal may also lose some effectiveness at higher weights. The copper IUD is not affected by weight at all. If weight is a factor, a double dose of levonorgestrel is sometimes advised, but ulipristal or an IUD is often the better answer. This is exactly the sort of detail a two-minute consultation settles.
What should you expect afterwards?
Your next period may come a few days early or late and may be heavier or lighter than usual. If it is more than seven days late, or unusually light, take a pregnancy test. If you vomit within about three hours of a pill, it may not have been absorbed and another dose is needed. Some medicines, including certain epilepsy treatments, St John's Wort and some HIV medicines, reduce the pills' effectiveness, which is another reason the IUD sometimes wins.
Emergency contraception prevents pregnancy; it does nothing about sexually transmitted infections. If the situation that led here also carried an infection risk, that is worth a separate, quiet conversation and, where appropriate, testing.
How quickly can you get it privately?
As of October 2026, a same-day telephone consultation with The Online GP is £59 and a video consultation £150. Emergency contraception can be prescribed promptly where it is appropriate, with clear advice on timing, weight, interactions and what to do next, and a referral arranged if a copper IUD is the right choice. Ongoing contraception can be sorted in the same conversation so you are not back here next month.
Book a same-day appointment or message us on WhatsApp. Confidential, unhurried and judgement free.
Evidence and limits
The Faculty of Sexual and Reproductive Healthcare clinical guideline on emergency contraception underpins the timing, weight and interaction points above: https://www.fsrh.org/Public/Standards-and-Guidance/Emergency-Contraception.aspx
This is general information, not personal medical advice. Emergency contraception works best early; if you are unsure which option fits, be seen the same day.