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What are “POPs”?

When considering oral contraceptives, two common options include combination oral contraceptives (COCs), which contain both estrogen and progestin, and progestin-only pills (POPs). In our What’s the difference between progestin and estrogen in birth control pills?, we looked at the major differences between these hormones and the benefits and drawbacks of COCs versus POPs.

Keep reading to learn more about progestin-only pills, how effective POPs are, potential side effects of this type of oral contraceptive, and women who may want to consider a POP over a pill that uses estrogen.

How do progestin-only pills work?

The key difference between POPs and COCs is that POPs do not contain estrogen. Instead, progestin is the primary hormone used to prevent pregnancy.

Progestin-only birth control pills prevent pregnancy by thickening the mucus of the cervix. This makes it harder for sperm to enter the uterus to fertilize an egg. As a synthetic form of progesterone (which is naturally produced in the body), progestin stops ovulation but this process is not always consistent.

Studies show that roughly four out of ten women who use progestin-only pills will still ovulate. Another way POPs prevent pregnancy is that it thins the lining of the uterus. This means any egg that is fertilized will have a harder time implanting itself to the wall of the uterus. Similar to other oral contraceptives, POPs do not prevent STDs (sexually transmitted diseases) or HIV. Because certain birth control methods do not provide skin-to-skin protection (oral contraceptives and IUDs), use a barrier method to protect against STDs, such as condoms.

POPs are taken orally and in order to be effective, must be taken once per day at the same time every day. Typical progestin-only pills come in a pack of 28 tablets, all of which contain active hormones with no placebo. However, Slynd®, a newer progestin-only pill, features 24 white active pills and four green inactive or placebo pills which helps to provide a scheduled withdrawal bleed that can be planned and anticipated.

Birth Control Pills

As with all medical products, read the patient package insert or ask your doctor to learn how to properly store your pills to ensure product stability and shelf-life.

How effective are progestin-only pills?

Clinical studies are performed to evaluate the effectiveness of POP products. These trials often look at both typical use and perfect use. When looking at typical use, approximately nine out of 100 women will become pregnant during the first year of using a POP. It’s important to keep in mind that these findings are based on other POPs that offer a 3-hour missed pill window. As the only POP with a more flexible 24-hour missed pill window, Slynd® has a Pearl Index of just 4.0 Pearl Index (2.3, 6.4; 95% CI).

Even if you’re taking your progestin-only birth control pills on schedule and ensure it’s safely stored, there are certain medications that may impact how effective the pill is in preventing pregnancy. Certain medications, such as Rifampin, some barbiturates, and griseofulvin, may make POPs less effective. Before taking birth control pills, inform your doctor of any other medication you may be taking.

The effectiveness of POPs may also be negatively impacted if you experience vomiting or diarrhea, resulting in your body not properly absorbing the pill. In this situation, women should use another method of birth control, such as a condom, for at least 48 hours.

Progestin products like Micronor® that use norethindrone offer a 3-hour window during which women must take the pill for it to be effective. Instead of using norethindrone, Slynd® uses drospirenone, another form of progestin. Slynd® is the only progestin-only pill that offers a 24-hour missed pill window. This means that you can be up to 24 hours late in taking your next Slynd® pill without compromising its effectiveness. However, it is still recommended that you take your pill at the same time every day for maximum effectiveness.

What are common side effects when taking progestin-only pills?

When using progestin-only pills, women may experience a lighter period with less blood flow and cramping. Certain women may also experience no periods at all when taking the pill. POPs have also been linked to a reduced risk of pelvic inflammatory infection, anemia, and endometrial cancer.

One adverse side effect when taking progestin-only pills, particularly those that use norethindrone, include erratic or unscheduled bleeding. Slynd®, unlike typical progestin-only pills, has a tolerable bleeding profile comparable to combined oral contraceptives. In clinical studies, there was as little as <1% (0.4%) discontinuation rate due to bleeding irregularities.

Other side effects of POPs may include headaches, acne, nausea, breast tenderness, lower sex drive, and weight gain.

group shot of 4 women with high BMI


Who should or shouldn’t take progestin-only pills?

Certain women who are more sensitive to estrogen may want to consider a progestin-only pill in order to avoid introducing additional hormones to their bodies.

Who should consider taking progestin-only pills?

Increased levels of estrogen may impact breast milk production during the postpartum period, so women who are breastfeeding will want to consider a POP instead of a combined pill.

Progestin-only pills are considered safe for older women (35 years old and older) who experience high blood pressure, blood clots, or migraine headaches with aura. Women who smoke should also avoid estrogen-based oral contraceptives, but POPs are a viable and safe alternative.

Who should not take any birth control pills, including progestin-only pills?

Women who have had breast cancer in the past or have a history of breast cancer in their family should not take a progestin-only pill. Additionally, those who experience severe cirrhosis, acute liver disease, abnormal uterine bleeding, or have benign or malignant liver tumors should not take POPs.

What are some common side effects of POP products?

With progestin-only pills, some of the common side effects include headaches, nausea, breast pain and tenderness, weight gain, decreased sexual drive, menstrual cramps, and acne. Speak to your doctor if side effects persist or worsen.

Choosing the progestin-only pill that’s right for you

When considering a progestin-only pill or combination birth control pill, always speak to a doctor to learn more about which product is right for you and your needs.

Do not take Slynd® if you:

  • have kidney disease or kidney failure
  • have reduced adrenal gland function (adrenal insufficiency)
  • have or have had cervical cancer or any cancer that is sensitive to female hormones
  • have liver disease, including liver tumors
  • have unexplained vaginal bleeding

If any of these conditions happen while you are taking Slynd®, stop taking Slynd® right away and talk to your healthcare provider. Use non-hormonal contraception when you stop taking Slynd®.

Click here to read more Important Risk Information and Full Prescribing Information.

Slynd® is a trademark of Chemo Research, S.L.

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