ellaOne® works by delaying ovulation so that any sperm in the female reproductive system cannot find an egg to fertilise, and so no pregnancy can occur.
When you have unprotected sex, sperm travel from the vagina, through the cervix and up the fallopian tubes where they wait for an egg. ellaOne® helps prevent or delay ovulation until all the sperm have died (5 days), so there is no egg for them to fertilise and no pregnancy can take place.
It is very important that you take ellaOne® as soon as possible after unprotected sex for it to be most effective.
If ovulation has already taken place, no morning after pill will be effective. It is very hard to know when you are ovulating as your cycle can change from month to month. By taking ellaOne® as soon as possible after unprotected sex, you reduce the risk of ovulating in that time.
The morning after pill only works by preventing ovulation, it can not cause an abortion and it will not have any effect in a case where an egg has already been fertilised.