Irregular periods may be one of the side effects of using emergency oral contraceptive pill, as it is a hormonal method of preventing pregnancy.
Since the pill works by introducing different hormones into one's system, it can affect their menstrual cycle. Some women may have lighter bleeding, and others may skip their periods entirely.
One of the most common side effects of the emergency contraception pill is getting one's period earlier or later than usual. If someone's period is more than a couple of weeks late, they may want to consider taking a pregnancy test. The pill can also make your period; lighter, heavier, longer, or shorter. The specific side effects vary widely among individuals, and different pills cause different side effects. Some common side effects include spotting, nausea, breast tenderness, and headaches.
Birth control pills act by ensuring that the ovaries do not release eggs. This action also leads to the thickening of the cervical mucus, which then acts as a barrier to the sperm. They may also make it difficult for an egg to implant itself in the lining of the womb.
Everyone is different, and the effects of pills are not always predictable. If a person has recently started taking a new pill, the body may need time to adjust, and this can cause a missed period. The iPill website has a "myth-busting" section, which states that "the Emergency Contraceptive Pills can cause fluctuation in your period cycle because of which the quality of bleeding may vary. This doesn't mean you are pregnant".