Plan B is an emergency contraceptive pill containing levonorgestrel, taken after unprotected sex or contraceptive failure. Its side effects are mild and short-lived, and the more important questions are usually about timing and what happens next.
Take it as soon as possible. Levonorgestrel emergency pills work best the sooner they are taken and are licensed for use within a defined window after unprotected sex. Waiting reduces how well it works, so this is not something to postpone.
Common hormonal medicine side effects
- Nausea, and occasionally vomiting
- Tiredness
- Headache and dizziness
- Lower abdominal pain or cramping
- Breast tenderness
- Spotting before the next period
- A period that arrives earlier or later than expected
These are short-lived, usually settling within a day or two. It is a single dose, not ongoing treatment, so there are no long-term effects to weigh.
If you vomit within a few hours of taking it, it may not have been absorbed. Check the leaflet and speak to a pharmacist, as another dose may be needed. See vomiting after the morning-after pill.
Bleeding, mood, skin, weight and cycle changes
Three things people are commonly unsure about:
- It does not end an existing pregnancy. Emergency contraception works mainly by delaying ovulation, so it prevents pregnancy rather than terminating one. If you are already pregnant it will not work and will not cause harm.
- It does not protect you for the rest of the cycle. You can become pregnant from sex in the days afterwards, so ongoing contraception still matters.
- It does not affect future fertility. Using it, even more than once, does not reduce your ability to conceive later.
Your next period may be early, on time or late. If it is more than about a week late, or unusually light, take a pregnancy test. See a late period after the morning-after pill and period changes after emergency contraception.
Serious warning signs that need medical attention
Get urgent medical help for severe lower abdominal pain, particularly three to five weeks afterwards, since this needs assessment to exclude an ectopic pregnancy. Also seek help for fainting, heavy bleeding with dizziness, or swelling of the face or throat.
Who may be at higher risk?
Things that reduce how well it works:
- Delay. Effectiveness falls the longer you wait, so take it as soon as you can rather than waiting for a convenient moment.
- Vomiting within a few hours of the dose.
- Some epilepsy medicines and rifampicin, and St John’s Wort. If you take any of these, say so, because a different option or a different dose may be needed. See St John’s Wort and birth control.
- Higher body weight, which may reduce the effectiveness of levonorgestrel emergency pills. A pharmacist may suggest an alternative.
A copper intrauterine device is the most effective form of emergency contraception and can be fitted within a defined window after unprotected sex. It is worth asking about, particularly if any of the above apply to you, and it can then continue as ongoing contraception.
Emergency contraception does not protect against sexually transmitted infections, and this is a reasonable moment to ask about testing.
What to discuss with your doctor, pharmacist or clinic
- Given when this happened, is this the right option, or would another be better?
- Do any of my medicines affect it?
- When should I take a pregnancy test?
- When can I start or restart ongoing contraception?
- Should I be tested for sexually transmitted infections?
If you have needed emergency contraception more than once, that is worth a conversation about ongoing options rather than a reason for awkwardness. Pharmacists provide this routinely.
Related contraception, HRT and hormonal medicine guides
- Emergency contraceptive pill side effects
- Morning-after pill side effects
- Hormonal contraception side effects
- When to see a doctor about hormonal medicine
- Report a hormonal medicine side effect
See also levonorgestrel side effects and Norlevo.
Medical Disclaimer: This content is for informational and educational purposes only and does not constitute medical diagnosis, prescription, or professional advice. Always read the patient information leaflet and consult a qualified doctor or pharmacist regarding any medicine or health concern.