Levonorgestrel is a single-dose contraceptive. If taken within 72 hours of the incident, there is a 95 percent chance of it being effective and preventing any unplanned pregnancy.

This emergency contraceptive tablet works with only one dose and can be kept on hand for any contraceptive accident or failure. It can be bought online and saves the need for an emergency appointment with your own doctor.

The active ingredient of 1.5mg of levonorgestrel works by stopping the release of eggs from the ovaries and also by preventing fertilisation of a released egg or it attaching itself to the lining of the womb.

Levonorgestrel is the active ingredient and its effectiveness is:

Within the first 24 hours: 95% effective

24 to 48 hours: 85% effective

48 to 72 hours: 58% effective

Levonorgestrel may have no effect if taken after longer than 72 hours after unprotected sexual activity. In such cases, consult your local doctor or there is the option of using EllaOne emergency contraception tablet which can be taken up to 5 days after unprotected sex.

Very few women are sick after taking Levonorgestrel but, should this occur within three hours of having taken the tablet, it is necessary to take a second replacement tablet, as the first dose will not have had sufficient time to be effective. If sickness still occurs, speak with your local doctor about a different emergency contraceptive method.

The feeling of being sick or nauseous will not affect Levonorgestrel.

Levonorgestrel may alter the regularity of your next period and may also lead to a much lighter or heavier period than is normal. If the next period proves to be more than five days late, either take a pregnancy test or consult your doctor.

Levonorgestrel protects you only for that one unprotected occasion and so contraception continues to be needed during the rest of the menstrual cycle. If you are using the patch or the contraceptive pill, you may also need the added protection of a condom for the rest of that menstrual period.

The following medicines may make Levonorgestrel less effective at preventing pregnancy:

Barbiturates and other medicines used to treat epilepsy (e.g.primidone, phenytoin, and carbamazepine)
Medicines used to treat tuberculosis (e.g. rifampicin, rifabutin)
Ritonavir (used to treat HIV)
Griseofulvin (used to treat fungal infections)
St John’s Wort (Hypericum perforatum - a herbal remedy)
Ciclosporin (suppresses the immune system)
If you take any of the above medicines you should discuss a more effective form of contraception with your GP or local family planning clinic.

If you suffer from any of the following conditions, Levonorgestrel may not be suitable for you and could be ineffective:

Bowel disease (e.g. Crohn’s disease) interferes with the way you digest your food
Severe liver problems
If you have ever had an ectopic pregnancy (where the baby develops somewhere outside the womb)
If you have ever had a disease called salpingitis (inflammation of the Fallopian tubes)
If you take any of the above apply you should discuss a more effective form of contraception with your GP or local family planning clinic.

Do not take Levonorgestrel if your period is already overdue as you may already be pregnant. You should see your GP or family planning clinic. If you have already taken Levonorgestrel but suspect that you may now be pregnant, there is no evidence that Levonelle will harm your baby.

Levonorgestrel should not replace your regular methods of contraception, such as the pill or condoms; these are more reliable and effective.

Please read the Patient Information Leaflet enclosed with your medicines before taking Levonorgestrel.

Levonorgestrel should be taken as soon as possible after unprotected sex; the sooner it is taken, the more effective it is at preventing unwanted pregnancy.
It is only effective up to 72 hours after, if it has been longer than this you should not take Levonorgestrel and see your GP to discuss emergency contraception.
If you are sick or suffer from diarrhoea within 2 hours of taking Levonorgestrel it may not have been absorbed and will not be effective. You will need to obtain another supply as soon as possible.
Levonorgestrel is not 100% effective at preventing pregnancy, however, it is 95% effective after 24 hours. It is important to try to take it within this window if possible. After this, the success rate becomes 85% and 58% after 48 and 72 hours respectively. If you cannot take Levonorgestrel within the first 24 - 48 hours after unprotected sex, you may wish to see your GP to discuss alternatives such as EllaOne.

If your next period has not arrived 5 or more days from when it was due you should take a pregnancy test.

Each Levonorgestrel tablet contains the active ingredient: 1.5mg of levonorgestrel.

It also contains the following inactive ingredients: potato starch, maize starch, colloidal silica anhydrous, magnesium stearate (E572), talc (E533b), lactose monohydrate.

If you do experience side effects from Levonorgestrel the most common can include:

Abdominal pains
Nausea or sickness
Diarrhoea
Dizziness
Breast tenderness
Headaches
Spotting or abnormal vaginal bleeding
A very small number of people may be allergic to Levonelle. This will show as a skin reaction including itchiness, rash and swelling of the face. If this occurs you should see your doctor immediately.

If you experience any adverse effects from taking your prescribed medicine it is important to let your doctor know immediately. In a medical emergency, you should contact the emergency services or go straight to your local Accident & Emergency.

https://www.nhs.uk/conditions/contraception/emergency-contraception/

https://www.medicines.org.uk/emc/medicine/16887/SPC