Emergency contraceptive pills (ECPs) can prevent pregnancy when taken within 5 days of unprotected sex. ECPs work primarily by preventing or delaying ovulation and may also affect egg and sperm transport. The levonorgestrel regimen is most common and involves taking one or two pills depending on the specific medication. ECPs are not intended for regular use and are meant only for emergency situations when unprotected sex occurred. While side effects can include changes to the menstrual cycle or nausea, ECPs are considered safe and effective for preventing pregnancy when used correctly.