In order to work, emergency contraception must be used soon after unprotected sex occurs. How soon after depends on a number of factors, including whether the pregnancy has implanted, the health of the woman and whether she may already be pregnant.
Emergency contraceptives in pill form are popularly known as the “morning-after” pill. They go by such brand names as Next Choice One Dose, Ella and Plan B One-Step and can be used up to five days after unprotected sex. However, manufacturers caution that the medications have a better chance of working if taken sooner rather than later.
The vast majority of the market uses Plan B One-Step, which has as much as 99 percent of the market share. Plan B was approved in 1999 and is available in generics Next Choice and Levonorgestrel tablets. Ella was approved in 2010. It is estimated that about 12 million packages are sold annually, according to research by the IMS Health and SymphonyIRI Group, both market research firms.
Morning-after pills contain either levonorgestrel or ulipristal acetate. Plan B One-Step is available over-the-counter without a prescription, but ulipristal may have a prescription for purchase.
The pills operate depending on where the woman is in her menstrual cycle. They can either prevent or delay ovulation, block fertilization or stop a fertilized egg from implanting in the uterus. The last function is debated among medical professionals, and there is some evidence that levonorgestrel doesn’t stop the fertilized egg from implanting. Whether Ella has the same limitation isn’t clear.