There is a choice when it comes to emergency contraception, and the different options work in different ways.
Here is a simple summary of how the 3 forms of emergency contraception actually work:
Copper Intrauterine Device (‘copper coil’) – this is the most effective form of emergency contraception. It works by preventing fertilisation and also prevents implantation (if necessary). It can be used up to 120hrs after unprotected sex (or 5 days after expected ovulation date – whichever is longer). It also has the added benefit of providing ongoing contraception if required (but it can be removed if that is not needed!)
Ullipristal acetate (ellaOne) – this is an oral contraceptive. It works by preventing/delaying ovulation and can be used up to 120hrs after unprotected sex. It is unlikely to prevent pregnancy if given after ovulation.
Levonorgestrel – this is another form of oral contraception. It also works by preventing/delaying ovulation. It has a licence for use up to 72hrs after unprotected sex (and is ineffective if given after 96hrs). It is also unlikely to prevent pregnancy if given after ovulation.
If you think you need emergency contraception I would recommend seeking medical advice as soon as possible, as all forms are more effective the sooner they can be started.