List of products in the National Drug Code with proprietary name aftera. Levonorgestrel is used by women to prevent pregnancy after birth control failure (such as a broken condom) or unprotected sex. This medication is an emergency contraceptive and should not be used as a regular form of birth control. It is a progestin hormone that works mainly by preventing the release of an egg (ovulation) during your menstrual cycle. It also makes vaginal fluid thicker to help prevent sperm from reaching an egg (fertilization) and changes the lining of the uterus (womb) to prevent attachment of a fertilized egg. Using this medication will not stop an existing pregnancy or protect you or your partner against sexually transmitted diseases (such as HIV, gonorrhea, chlamydia). This medication may not work well in women over a certain weight (for example, greater than 164 pounds or 74 kilograms), or if you have used certain other medications within the past month. This effect can result in pregnancy. Talk to your doctor for more details and to see if this medication is right for you (see also Drug Interactions section). Check the ingredients on the label even if you have used the product before. The manufacturer may have changed the ingredients. Also, products with similar names may contain different ingredients meant for different purposes. Taking the wrong product could harm you.