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How Effective Are Progestin-Only Birth Control Pills?

Emily Maurer

Medically reviewed by Emily Maurer, NP on September 17, 2020

Progestin-only birth control pills, also known as minipills, are a completely safe and effective form of hormonal birth control. Though less popular than the combination pill, the minipill can deliver the exact same level of pregnancy protection when taken properly.

Still, the minipill is its own unique form of birth control, and women who take it need to be aware of a few key differences between it and other methods.

How effective is the minipill?

Most birth control combination pills work by increasing your body’s levels of estrogen and progestin, two naturally occurring hormones that regulate the body’s reproductive cycles. Minipills only contain progestin, slightly altering their overall efficacy. Like combination pills, minipills prevent unwanted pregnancy by halting ovulation and thickening the cervical mucus — making it impossible for egg fertilization to occur.

When used exactly as prescribed, minipills are up to 99% effective at preventing pregnancy. In reality, however, minipills are actually somewhere between 87 and 91% effective, meaning that between 9 and 13 out of 100 women who take the minipill become pregnant every year. 

The failure rate of minipills is slightly higher than those of most other forms of hormonal birth control, mostly due to the minipill’s more specific usage instructions. The minipill must be taken at the same time every single day in order to stay effective — a deviation of just a few hours can lower your body’s protections against pregnancy.

Maximizing Minipill Efficacy

First things first: when you start taking the minipill determines how soon it becomes effective. If you take your first pill within the first 5 days after the start of your period, you will be protected against unwanted pregnancy immediately. Otherwise, you’ll need to use another form of birth control such as a condom for at least 48 hours after your first pill until the pregnancy protection begins. 

Taking the pill with the appropriate regularity can be a bit trickier. If you take a pill 3 or more hours later than you normally do, use condoms or another form of birth control for a minimum of 48 hours so your body can get its progestin levels back where they need to be. The same advice applies if you vomit in the hours after you take a pill, as your body probably didn’t have time to fully absorb the hormones. 

If you forget to take the pill for several days in a row or have some other kind of long-term disruption to your birth control, tell your doctor. While you may just be able to start over with a new pack of pills, it’s best to be sure that there aren’t any other factors you need to take into consideration.

Why take the minipill?

Even though minipills are slightly less effective than combination pills, they’re still a valuable option for many women. Because minipills contain progestin alone, they’re ideal for women looking to maintain their natural levels of bodily estrogen. 

Women who are at risk of conditions such as blood clots or high blood pressure are usually advised to take the minipill, because the estrogen in other hormonal birth control methods can more than double a woman’s chances of developing blood clots.

For this same reason, women over the age of 35 with a history of smoking are advised to consider the minipill as a birth control option, since both age and smoking are factors that can interfere with blood flow. 

Another common reason women opt for the minipill is breastfeeding: high levels of estrogen can reduce a woman’s supply of breastmilk. While not all women will find that estrogen-containing birth control affects their milk output, those looking to err on the side of caution often consider the minipill a good alternative.

Minipill Alternatives

Minipills aren’t the only option out there for women looking for estrogen-free birth control. Both the shot, the Nexplanon implant and hormone-containing IUDs protect against unwanted pregnancy using progestin alone. 

In addition, the birth control shot, implant and the IUD don’t require the constant upkeep of the minipill. Shots need to be taken approximately once every 12 weeks in order to be effective, the implant is good for 3 years and most IUDs can last for between 3 and 5 years at a time. For women who want a progestin-only birth control option but are worried that minipills might not be effective enough for them, there are methods out there.

Finding the right birth control method for you can be an overwhelming process. With the vast number of options out there for you to choose from, it can feel impossible to know what the best one is. Get started by answering some questions from a Nurx provider to get customized recommendations from our experts.

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