Levonorgestrel 1.5mg is the generic version of Levonelle. The treatment is a synthetic version of the hormone Progesteroneand is understood to work in two ways: Stopping the ovaries releasing an egg and preventing sperm from fertilising an egg already released.
The dose can be taken up 72 hours after sex, but should be taken as soon as possible after sex to increase it's effectiveness.
Levonorgestrel may cause side effects and is not suitable for all women. More detailed information can be found in the Dr Andrews Clinical Fact Sheet on Emergency Hormonal Contraception.