Levonorgestrel is a short-acting contraceptive pill that significantly inhibits ovulation and prevents the implantation of a pregnant egg. It exerts a fast-acting contraceptive effect by increasing the mucus viscosity of the cervix, thus increasing the resistance to sperm penetration. This drug is generally used for emergency contraception in women in case of unprotected or other contraceptive errors, which may include slipping or breaking of the condom, uncontrolled in vitro ejaculation, or miscalculation of the safety period. It is generally recommended that one pill be taken within 72 hours of intercourse. The earlier this pill is taken, the more effective it is, and it can be taken at any time during the menstrual cycle.