Levonorgestrel emergency contraception: important information for women taking other medicines. Some medicines or herbal remedies that contain the ingredient St. John's wort, might reduce how well levonorgestrel emergency contraception works. Tell the doctor, pharmacist or nurse if you are currently taking a medicine to treat any of the following, or if you have used one in the past 4 weeks: epilepsy, tuberculosis, HIV, a fungal infection, or if you have taken any herbal remedies that contain the ingredient St. John's wort.