Emergency contraception can reduce the chance of pregnancy after unprotected sex or contraceptive failure, but it is not guaranteed to work in every situation. If you are worried it has not worked as expected, understanding why can help you decide what to do next.
Our guide explains how timing, ovulation, medicines, vomiting and other factors can affect emergency contraception, along with clear next steps. If you are unsure at any point, a pharmacist can help you understand your options quickly and discreetly.
You can start a confidential online consultation with us here at WePrescribe for personalised advice based on your situation.
Timing Of Use In Relation To Ovulation
Emergency contraception pills mainly work by delaying or preventing ovulation, so they may be less effective if ovulation has already happened.
- Sperm can survive in the body for several days
- Pregnancy can still occur if ovulation happens shortly after sex
- Emergency contraception is most effective before ovulation
Because timing is not always clear, it is often safer to get advice rather than rely on estimates.
Why It Is Hard To Know Exactly When Ovulation Happened
Ovulation does not always happen at the same time each cycle.
- Periods can vary from month to month
- Stress, illness or travel can affect timing
- Apps and trackers are only estimates, not medical tools
If your decision depends on ovulation timing, a pharmacist can help you assess your risk more accurately.
Delays Between Unprotected Sex And Taking Treatment
The sooner emergency contraception is used, the more effective it usually is.
Waiting can reduce your options, especially after a few days.
What to do based on timing
| Time since sex | What to do |
| Within 24 hours | Seek emergency contraception as soon as possible |
| 1–3 days | Do not delay, options are still available |
| 3–5 days | Seek urgent advice, options may be more limited |
| Over 5 days | Speak to a pharmacist, GP or sexual health clinic |
Do not wait to “see what happens.” Acting quickly gives you more options.
Interactions With Other Medications Or Supplements
Some medicines and herbal remedies can reduce the effectiveness of emergency contraception.
This includes certain medicines that affect how hormones are processed in the body, as well as herbal remedies such as St John’s wort.
Bring this to your consultation
- Current medications
- Recent medications (last few weeks)
- Herbal supplements
- Any long-term conditions
If you are unsure whether something may interact, it is safer to mention it and get advice.
Body Weight And Its Potential Influence On Effectiveness
Body weight or body mass index may influence how well some emergency contraception pills work, but this varies and should be discussed individually.
- It does not mean emergency contraception will not work
- It does not mean you have done anything wrong
- It simply means your options may need to be reviewed more carefully
A copper intrauterine device is not affected by body weight based on current evidence.
Vomiting Or Digestive Issues After Taking A Dose
Vomiting soon after taking an emergency contraception pill may mean the dose has not been absorbed properly.
Guidance suggests that if vomiting happens within a few hours, further advice is needed quickly.
What to do:
- Do not assume the dose has worked
- Do not wait for your next period
- Seek advice from a pharmacist, GP or sexual health clinic
If this has happened, you can speak to a WePrescribe pharmacist online for prompt, discreet guidance.
Incorrect Use Or Misunderstanding Of Instructions
Emergency contraception may be less reliable if it is not used as intended.
Common issues include:
- Taking it later than recommended
- Not seeking advice after vomiting
- Having further unprotected sex afterwards
- Assuming one dose provides ongoing protection
If you are unsure whether you have used it correctly, it is worth checking rather than waiting.
Situations Where Additional Contraception May Be Needed
Emergency contraception does not replace regular contraception, and extra protection may be needed afterwards.
Practical next steps
- Use condoms or avoid sex until advised otherwise
- Consider starting or restarting contraception
- Follow the pharmacist’s or clinician’s advice
- Take a pregnancy test if your period is late or unusual
If you need ongoing protection, exploring regular contraception options can help reduce future risk.
What To Do If You Think Emergency Contraception Did Not Work
If your period is late, unusual, or you have pregnancy symptoms, take a pregnancy test and seek advice.
When to act
- If your period is late
- If your bleeding is different from usual
- If you have symptoms such as nausea or breast tenderness
When to seek urgent help
- Severe lower abdominal pain
- Heavy or unusual bleeding
- Feeling faint or unwell
Contact NHS 111 for urgent advice, or call 999 in an emergency.
If you are unsure what has happened or what to do next, speaking to a pharmacist can help you understand your risk and your options without judgement.
One of our WePrescribe pharmacists can review your situation confidentially, including timing, symptoms and any medicines you have taken, and guide you on whether you may need a pregnancy test, further care or ongoing contraception.
Taking that step can give you clarity and reassurance, rather than waiting and worrying.
