Often called 'the morning after pill', you can take the emergency contraceptive pill to try and prevent pregnancy. It will only work if you haven't ovulated.
Levonelle
Levonelle contains levonorgestrel, a synthetic (man-made) version of the natural hormone progesterone produced by the ovaries. Taking it's thought to stop or delay the release of an egg (ovulation). Levonelle has to be taken within 72 hours (3 days) of sex to prevent pregnancy. It doesn't interfere with your regular method of contraception.
ellaOne
ellaOne contains ulipristal acetate, which stops progesterone working normally. This also works by stopping or delaying the release of an egg. ellaOne has to be taken within 120 hours (5 days) of sex to prevent pregnancy.