The morning-after pill (emergency contraception) is estimated to prevent about 85% of pregnancies. It is thought to work by:
a) Stopping the ovaries from releasing an egg,
b) Preventing sperm from fertilizing any egg that may have already been released; or, (importantly)
c) Stopping a fertilized egg from attaching itself into the womb lining.
Since this reversible contraceptive device acts after the sperm has fertilized the egg and the device merely prevents a fertilized egg from implanting itself into the womb lining, then the ruling on such contraceptive devices would be similar to that of carrying out an abortion at an earlier stage, which is impermissible unless there is a genuine and valid reason.
Therefore, the morning-after pill will have the same ruling as the loop (an intrauterine device), for it may work by stopping a fertilized egg from attaching itself into the womb, as mentioned above. Thus, the rules of an early abortion would apply in this case also; and hence it should only be used in extreme medical conditions.
In conclusion, the ruling on employing the loop, the morning-after pill or any other method that may act after the egg has been fertilized as a means of contraception is somewhat different to the general ruling on reversible contraception (al-azl). Reversible contraception is generally permitted if practiced on an individual level, whilst employing any method that may prevent a fertilized egg from implanting itself into the womb will not be allowed except in certain medical conditions, for which one should consult a reliable scholar of knowledge and piety.