The second dose is taken 12 hours later. Emergency contraceptive pills are very effective. If taken within 24 hours of unprotected sexual intercourse, they will prevent at least three out of four pregnancies that would have occurred if no emergency contraception had been taken. Emergency pills are more effective the sooner the first dose is taken after sex . Research shows that progestogen-only methods are more effective than using combined oestrogen and progestogen emergency pills.
Most women can use emergency pills.
However, if you are taking certain prescribed or over the counter medicines, or suffer from certain illnesses such as migraine, some emergency pills will not be suitable. Tell your doctor, pharmacist or family planning clinic about any medicines you are taking or any illnesses you may have. You may feel sick or vomit. This is much less likely with progestogen-only emergency pills. However, if you do not get a normal period within three weeks, think you may be pregnant or want to talk about using regular contraception go and see a doctor or nurse.