Questions You Have About Birth Control

Dr. Nancy Shannon: Sure!

Progestin-only birth control pills, like all forms of hormonal birth control, work by altering the patterns of naturally occurring hormones in the body. But birth control pills that contain both estrogen and progestin work mainly by preventing ovulation, while progestin-only pills work by thickening cervical mucus, making it difficult for sperm to enter, and thinning the lining of the uterus to prevent pregnancy. Progestin-only pills can interfere with ovulation, but don’t always do so consistently. 

When taken correctly, progestin-only pills are just as effective as combination pills, but it’s essential that you take POPs on time. You must take them within the same three-hour window every day, and if you miss that three-hour window you should use a condom any time you have sex for the next 48 hours. 

You should also know that you take most types of progestin-only pills every day, without a placebo week (though one brand of POP, called Slynd, has four placebo pills at the end of each pack). You can’t use progestin-only pills to reliably skip periods, and you may experience spotting throughout the month as your body gets used to the POP. However, after the first few months, most people on POPs experience much lighter periods, and some stop having periods at all until they stop taking the POP.

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