can tell if it worked when you get your period, if you don’t, take a pregnancy test. that is how and when you know whether it did work. the morning after pill is a one time thing.... i have issues with other pills so i have to rely on the morning after pills at times but with periods i know how it works but as i don't have my periods back yet wondering how does it really work! i'm not to sure how you will tell without your period. 