Two oral emergency contraceptives are available in the UK: ellaOne (ulipristal acetate) and Levonelle (levonorgestrel). A third option — the copper IUD — is more effective than either pill but requires fitting by a clinician within 5 days. This article explains how each works, when each is used, and what to do afterwards.

How ellaOne (ulipristal acetate) works

Ulipristal is a selective progesterone receptor modulator. It works mainly by delaying or stopping ovulation, even close to the time when ovulation is about to occur. This wider effective window is one reason it has higher efficacy than levonorgestrel later in the cycle.

ellaOne is licensed for use up to 120 hours (5 days) after unprotected sex. Earlier is better, but it remains effective across the whole window.

How Levonelle (levonorgestrel) works

Levonorgestrel is a synthetic progestogen. It works primarily by delaying or stopping ovulation, but it is less effective than ulipristal when ovulation is imminent. Its window is 72 hours (3 days) after unprotected sex — though efficacy drops as time passes within that window.

Levonelle is widely available, generally lower in cost than ellaOne, and is what most pharmacies stock as standard. A higher dose is recommended for patients with a BMI over 26 or a body weight over 70 kg.

Time windows after unprotected sex

The earlier you take any emergency contraceptive, the more effective it is. As a rough framework:

  • 0 to 72 hours: either pill is an option. ellaOne is generally more effective.
  • 72 to 120 hours: only ellaOne or a copper IUD is appropriate.
  • Any time within 5 days: a copper IUD is the most effective single intervention.

Interactions and what to avoid

Hormonal contraception interactions are the most clinically important here. Levonorgestrel can be used alongside ongoing hormonal contraception, but ulipristal is different — taking progestogen (including starting or resuming your regular pill) within 5 days of ellaOne can reduce its effectiveness. Clinicians will advise the right approach for your situation.

Both pills can be affected by enzyme-inducing medications such as certain epilepsy or rifampicin-based regimens. If you take regular prescription medication, mention it at consultation.

Side effects and follow-up

Common side effects of both pills include nausea, headache, fatigue, dizziness, and changes to the timing of the next period. If you vomit within 3 hours of taking either pill, you may need to take another dose — speak to a clinician.

Your next period can come earlier or later than usual. If it's more than 7 days late, take a pregnancy test. Emergency contraception does not protect against STIs and is not as effective as regular contraception — it is for use after an accident, not as a routine method.

What to do next

After taking either pill, the conversation should turn to ongoing contraception. If you don't have a method you trust, your clinician will discuss the options — combined pill, progestogen-only pill, implant, IUD, injection — and what fits your life. A consultation through Farmeci can review your situation and prescribe regular contraception where appropriate.