When a regular method has let you down or was missed, levonorgestrel gives you a clear, well established way to lower the chance of pregnancy. A single 1.5 mg tablet works mainly by delaying ovulation, the moment at which pregnancy could otherwise begin, and it has been used safely by women for this purpose for decades.

Timing is everything. The tablet can be taken up to seventy two hours after unprotected sex, but it is most effective the sooner it is taken, so there is real value in not waiting. It is intended as a backup for occasional use rather than a routine method, and it offers no protection against sexually transmitted infections.

Most women have no trouble with it. Some notice mild nausea, tiredness or a headache, and the next period may arrive a little earlier or later than expected. If you are sick within two hours of taking it, you may need another dose.

Take the single tablet as soon as possible after unprotected sex, ideally within twelve hours and no later than seventy two hours. It can be taken with or without food. If you vomit within two hours, take another tablet.

Levonorgestrel 1.5 mg, the active ingredient.

Nausea, tiredness, headache, lower abdominal pain and spotting can occur, and the next period may shift earlier or later. The effects are short lived.

For emergency use only, not a routine method, and it gives no protection against sexually transmitted infections. It will not end an existing pregnancy. If your period is more than a week late, take a pregnancy test.