ellaOne: ellaOne contains and active ingredient called ulipristal acetate. This chemical prevents or delays your ovaries from releasing an egg (ovulating) This protects you against pregnancy.
Levonelle: contains a synthetic hormone like substance called levonorgestrel. It prevents about 84% of expected pregnancies when you take it within 72 hours of having unprotected sex. It will not prevent a pregnancy every time and is more effective if you take it as soon as possible after unprotected sex. It is better to take it within 12 hours rather than delay until the third day.