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What is a progestin-only contraceptive pill or “POP”?

A progestin-only contraceptive or the “mini-pill” is one kind of birth control pill. Regular birth control pills contain two hormones: estrogen and progesterone. The mini-pill has only progesterone in it and is highly effective with a failure rate of 0.3% with perfect use and 9% with typical use.

How does the POP work?

The hormone causes the mucus between your cervix and uterus to thicken which helps to block sperm from ascending into the uterus. It also causes the lining of the uterus to become thinner. Finally, the mini-pill can stop your body from releasing an egg, so fertilization cannot take place.

Starting POP

Switching from Estrogen Containing Contraceptive Pills 

Skip the 7 inactive pills at the end of the pack and instead start the POP’s the day after the last active pill. Use a back-up method for the first 2 days. 

First Day Start 

Take the first pill on the first day of your period. Take one pill daily at the same time every day, even during your period. Use a back up method, such as condoms or spermicide for the first 7 days. 

Today Start 

Start the pill today. If you have had unprotected intercourse since your last period, perform a pregnancy test prior to starting the pill. If it is negative, start the pill today. Use another method of birth control such as condoms or spermicide for the first 7 days. 

As soon as you finish one pack, begin the next one. Start your next pack even if you are still bleeding or have not started your period. Continue taking one pill every day.

Missing Pills 

If you miss one POP take it as soon as you remember it, even if that means taking two pills in 1 day. If you are more than 3 hours late taking a POP, use a back-up method (condoms or spermicide) of birth control for the next 7 days.

If you miss 2 or more POP in a row, there is an increased chance you could become pregnant. Immediately start using your back-up birth control method. Restart the POP by taking 2 pills a day for 2 days. If your menstrual period does not begin within 4 - 6 weeks, see your clinician for an exam or perform a home pregnancy test. 

If you have had intercourse without adequate protection because you missed one or more pills, you may be able to use the emergency contraception pill to prevent an unwanted pregnancy. Contact University Health Services or your clinician for information about the “morning after” pill.

Missing Periods 

Keep track of your periods while you take the POP. If you have more than 45 days with no period, then you may want to do a home pregnancy test or see your clinician for an exam and pregnancy test.


  • Some women may experience irregular bleeding and menstrual periods. Spotting between periods is fairly common. Some women stop having periods for several months at a time. Once a pregnancy is ruled out, this is not harmful. 
  • The POP is a very low dose contraceptive and there is a very narrow margin of error. If you miss a pill or take a pill late you could be at risk for pregnancy. The pill must be taken every single day at the same time daily to be effective. 
  • Increased risk of functional ovarian cysts 
  • Slight increased risk of an ectopic pregnancy 


  • The POP has no estrogen side-effects and can be taken by women that have had complications or side effects from using the estrogen-containing birth control pill. 
  • Nursing mothers can take the POP without a change to their milk supply, preferably after the baby is six weeks old. 
  • Decreased risk of endometrial cancer 
  • Decreased risk of anemia

 The POP does not protect you from sexually transmitted infections. If you are at risk for a sexually transmitted infection, it is a good idea to always use a condom even when on the pill.


In an emergency go to Mount Nittany Medical Center or call 911 for an ambulance.

This content is reviewed periodically and is subject to change as new health information becomes available. This information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.

Approved by the UHS Patient Education Committee Revised 05/22/18

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