The birth control pill is the most popular form of contraception for American women but, unfortunately, the pill’s effectiveness heavily depends on how it’s taken. Doctors urge that women make it a habit to take the pill at the same time every day, but why is this even a rule, and what exactly would happen if you broke it?

The birth control pill is arguably the most well-known “pill” in the English vernacular. It's responsible for preventing countless unplanned pregnancies throughout the world every day, and Forbes even credited the pill for helping advance the woman’s equal rights movement. The American College of Obstetricians and Gynecologists explained that, when used perfectly, around one in every 100 women will become pregnant over the course of a year. When used typically, however, that number jumps to eight women in every 100. Doctors urge that you make it a habit to take the pill at the same time every day, but why does this punctuality matter so much? Well, it has to do with what the pill actually does to a woman’s body.

How The Pill Works

Many women simply swallow a mysterious pill every day knowing that it’ll keep them baby-free without completely understanding what’s happening on a biological level.

There are two main types of birth control pill: progestin-only pills and combination pills, which contain both progestin and estrogen. These hormones work to prevent pregnancy in several different ways. First, they prevent ovulation by tricking the body to never realize that it’s time for it to release eggs. These same hormones also thicken the mucus in the cervix, making it more difficult for tiny sperm to enter. In addition, they also thin the lining of the uterus, so that if by chance an egg is released and it does meet up with a sperm, it will not be able to latch onto the uterine lining and begin a pregnancy.

Why Time Is Of The Essence

Progestin pills, also known as mini pills, are the less popular of the two pill types and are the only time-sensitive forms of birth control medication. These pills are slightly less effective than combination birth control pills. However, some women opt for mini pills over combination birth control because they carry a lower risk of serious health complications.

According to Planned Parenthood, if you are late taking the POP pills by more than three hours, it’s important that you use a second form of birth control, such as a condom. This is because the active ingredient in POPs, progestin, does not stay in the body’s system for very long — typically 24 hours. When the pill is taken later, a woman’s body has had time to revert back to its natural fertility and release an egg. If she has sex after taking a late pill she has a higher chance of becoming pregnant. Even if you’re only a few hours late, it’s strongly advised that you use backup birth control.

Doctors still advise that women take the combination pill at the same time every day, but this is more so that they make the pill a habit and are less likely to go a day without taking it. Due to the duo hormones in the combination pills, women are still protected even if they are a few hours late taking their medication. But it’s still essential that you take these medications every day, Bedsider explained.

If you miss more than two combination birth control pills, then you are in danger of pregnancy. In these instances it’s recommended that you begin taking your pills again on your regular schedule and use a second form of birth control for the following week.