Levonorgestrel is a manufactured hormone which is used in numerous methods of birth control.

If levonorgestrel is taken in pill form within 120 hours of unprotected sex, it can be used as an emergency birth control method. In most countries, levonorgestrel can be provided by a pharmacist after consultation with a patient and so a prescription is not needed. However, levonorgestrel is less effective with the passing of hours and can only be used BEFORE pregnancy has occurred.The mechanism of levonorgestrel as an emergency birth control method works by inhibiting ovulation, thus preventing fertilisation, and thickening of the mucosa of the cervix.

Levonorgestrel can also be combined with estrogen in order to produce the combined oral birth control pill, an extremely popular method used as a preventative measure by women worldwide.

Very common side effects (10% of subjects reporting) of levonorgestrel include dizziness, uterine bleeding/pain, fatigue, heavy menstruation and headache/nausea. Diarrhoea, vomiting and painful menstruation can also occur but are less common and usually dissipate after 48 hours.