How does the morning-after pill work? Levonorgestrel explained

When should you seek emergency contraception?

Seek advice as soon as possible after unprotected sex or a contraceptive failure. The levonorgestrel emergency contraceptive pill is used within 72 hours under the cited UK guidance; sooner is better. Do not wait for a routine online assessment if that delays care.

Other options have different time windows. A pharmacist or sexual-health service can help choose an appropriate method based on when sex occurred, medicines you take and your circumstances.

How levonorgestrel works

Levonorgestrel mainly prevents or delays ovulation. It does not end an established pregnancy. It cannot guarantee that pregnancy will be prevented, protect against sexually transmitted infections or provide continuing protection for sex later in the cycle.

A pregnancy risk cannot be calculated reliably from a single generic success percentage. Timing relative to ovulation, further unprotected sex and interacting medicines matter.

Compare timing rather than incompatible percentages

The copper IUD may sometimes be considered according to ovulation timing, which a clinician must assess. Do not rule out care yourself because a pill's window has passed. Do not combine emergency contraceptive pills without professional advice.

Product instructions and vomiting

The UK Levonelle 1500 product information specifies one 1.5 mg tablet within 72 hours and another tablet if vomiting occurs within three hours. This is product-specific information, not a universal vomiting threshold for all emergency contraceptives.

If you vomit soon after a dose, contact a pharmacist or clinician promptly with the pack name and timing. Do not guess whether another dose is needed. Tell them about medicines used during the previous four weeks, including epilepsy treatments and St John's wort: an alternative method may be necessary.

Weight or BMI can affect the discussion, but uncertainty in the evidence is not a reason to withhold timely advice or rely on an unsupported weight cutoff.

After taking it

Ask when to restart or continue your usual contraception and how long additional protection is needed. Guidance differs between levonorgestrel and ulipristal.

A pregnancy test three weeks after the last unprotected sex helps check the outcome. Seek advice sooner for an unusually late or abnormal period or pregnancy symptoms. Severe abdominal pain or fainting needs urgent assessment.

Breastfeeding advice also depends on the exact product. Ask a pharmacist rather than applying one pill's leaflet to another. Emergency contraception should remain a prompt local-care decision.

Information and clinical decisions

This guide provides general information, not a diagnosis or personal treatment plan. Any clinical assessment and prescribing decision rests with an independent clinician. Prescrivia is a technology intermediary, not a medical provider or pharmacy; it does not prescribe, sell or dispense medicines. Assessment does not guarantee a prescription, medicine availability or a health outcome.

Further reading: our period-delay guide, for a different purpose from emergency contraception.

Read about online consultations and their limits. Service information must not delay urgent local care.

Sources

1. NHS: emergency contraception — UK pill and copper-IUD timing and the copper IUD's greater effectiveness.
2. Levonelle 1500 UK product information — Single-tablet regimen, three-hour vomiting rule, mechanism and enzyme-inducing medicine considerations for this product.
3. Devon Sexual Health: emergency contraception — Follow-up pregnancy testing three weeks after the last unprotected sex and prompt advice.
4. Levonelle One Step UK patient leaflet — Product-specific precautions, pregnancy warning symptoms and breastfeeding advice.

See the current clinical, legal and language review statuses for this edition. Source checks are editorial work, not approval.