Any hormonal preparation taken in the form of a pill to prevent conception (see birth control). The most common form is the combined pill, which contains an oestrogen and a progestogen. Both act to suppress ovulation, while the progestogen additionally causes changes in the viscosity of cervical mucus and alters the lining of the womb, both of which decrease the chances of fertilization should ovulation occur. The so-called ‘minipill’ contains only a progestogen and has fewer side effects than the combined pill. Emergency contraception (the so-called ‘morning-after pill’), is designed to prevent pregnancy after unprotected sexual intercourse. There are several types. One contains the synthetic progestogen levonorgestrol, which delays ovulation and has to be taken within 72 hours of intercourse. Another type contains ulipristal acetate, which also delays ovulation, and is effective for up to five days following intercourse.