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

A progestin-only contraceptive pill(POP) or the “mini-pill” is one kind of birth control pill. Regular birth control pills contain two hormones: estrogen and progesterone. The most common POP containsonly norethindrone and is highly effective with a failure rate of 0.3% with perfect use and 7% with typical use.It is a good option for those women who have a medical condition in which birth control pills containing estrogen would be contraindicated and for those who have unwanted side effects from estrogen containing birth control pills.

How does the POP work?

You must take a pill the same time every day. The POP works by thickening cervical mucus to inhibit sperm migration, suppression ovulation, slowing movement of an egg through the fallopian tubes, and thinning the endometrium. Ovulation is not consistently suppressed with the norethindrone POP, and approximately half of the women still ovulate. Therefore, the effects of the norethindrone POP on cervical mucus and endometrium represent the critical factors in factors in prevention of conception.

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 7 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 weeks perform a home pregnancy test. If negative, and menses does not begin in 2 weeks, repeat the pregnancy test. If negative, continue the pills, if positive, stop the pills and call your provider or UHS.

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 (ECP) to prevent an unwanted pregnancy. If less than 3 days since unprotected intercourse, emergency contraception brand,Plan B One Step,and other generic ECPsare available over the counter without a prescription. If greater than 3 days and less than 5 days since unprotected intercourse, please contact University Health Services or your clinician for information about Ella, another ECP which requires a prescription.

Illness symptoms and use of medications that may interfere with efficacy: if having severe vomiting and or diarrhea within 4 hours of taking POP, continue the pill and use back-up method of birth control until 48 hours after symptoms are over. Medications such as Rifampicin, certain seizure medications and some anti-retroviral drugs can lessen effectiveness of POP. Always inform your provider of all of your current medications.

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 and/or consult with your clinician.


  • 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 POPis 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(within a 3 hour window)daily to be effective.
  • Increased incidence of functional ovarian cysts.
  • Slight increased risk of an ectopic pregnancy. Report any unexplained abdominal or pelvic pain to your provider, if severe, seek immediate medical evaluation.y 


  • 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 06/10/2020

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Progestin Only Contraceptive Pill


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