One of the known side effects of the emergency oral contraceptive pill is changes in menstrual bleeding patterns.
In general, your menstrual period should still arrive within a week from its usual expected date. Research has demonstrated that if you take emergency contraception earlier in your menstrual cycle, your period may come slightly earlier, while if you take it later in your cycle, your period may be slightly delayed.
Nevertheless, these variations should not exceed a week and if you experience prolonged delay in the arrival of your menses, you should consider a urine pregnancy test.
You may also experience a longer menstrual period than usual. Intermenstrual bleeding (known also as "spotting") may also occur.