Progesterone-Only Birth Control

Progesterone-only birth control is a type of hormonal birth control that does not contain synthetic estrogen. Instead, it uses a synthetic form of progesterone called progestin.

The oral form of this type of birth control is also called the minipill. Because it does not contain estrogen, the minipill may have fewer side effects than other forms of hormonal birth control.

Progestin-only birth control is considered a safer form of birth control for those who are over the age of 35, smoke, or are at risk for heart attack or stroke. It is between 93% and 99% effective in preventing pregnancy.

Here's what to know about who should consider progestin-only birth control, what the options are, and the potential risks.

How Progestin-Only Birth Control Works

Progestin-only birth control contains only progestin, a synthetic form of the hormone progesterone. In the body, progesterone is a sex hormone produced in the ovaries. It plays a role in the menstrual cycle and the early stages of pregnancy.

Progestin-only birth control works by thickening cervical mucus, making it harder for sperm to enter the uterus. It also helps prevent ovulation, which occurs when your ovary releases an egg. It is not as good at preventing ovulation as other types of birth control pills, however. This makes it slightly less effective than other birth control methods although the minipill is still considered very effective at preventing pregnancy.

Progestin-only birth control is considered safer for certain people, and it may have fewer side effects than birth control pills that contain estrogen.

Progestin-only vs. Combination Birth Control Pill

In comparing these two types of hormonal birth control, there are some differences:

• Combination birth control pills contain two hormones—both progestin and estrogen—instead of just progestin.
• Progestin-only birth control has fewer side effects, but it may be slightly less effective at preventing pregnancy. 
• All progestin-only pills contain the same amount of progestin (all pills are "active"), so you must take one every day and at the same time every day, whereas combination birth control pills have either 21 or 24 active pills.
• The progestin dose is higher in combination birth control pills compared to progestin-only pills.

Why Use Progestin-Only Birth Control?

Your healthcare provider may recommend a progesterone-only birth control method if:

• You're breastfeeding: Some research has suggested that the estrogen in combination birth control pills may inhibit breast milk production. Progesterone alone does not have this effect.
• You're at increased risk for cardiovascular problems: Progestin-only birth control is considered a safer option if you're at risk of heart disease or stroke. Estrogen, by contrast, is known to increase cardiovascular risk, particularly if you have high blood pressure, a history of blood clots, or are over 35 and smoke.
• You want to avoid taking estrogen: Combination pills sometimes cause headaches or nausea, but the progestin-only minipill doesn't have these side effects.

Who Shouldn't Use Progestin-Only Birth Control

Progestin-only contraception may not be appropriate for you if:

• You are at high risk for or have had breast cancer: While the research on this is not definitive, some studies have shown an association with progestin-only birth control and breast cancer.
• You have liver disease: Some evidence has shown that progestin can potentially damage the liver.
• You take anti-seizure medications: Some anti-seizure medications break down hormones in your body and may reduce the effectiveness of a progestin-only pill.
• You have had bariatric surgery: Bariatric surgery may affect the way your body absorbs these medications and may make them less effective.
• You have trouble remembering to take medications at the right time: While combination birth control pills don't have to be taken at the exact same time every day, the minipill does. There are other options, such as an intrauterine device (IUD), that don't require you to take any pills.

Common Side Effects

Progestin-only birth control pills share common side effects, some of which will resolve over time. They may include: 

• Headache
• Nausea
• Spotting or irregular vaginal bleeding
• Amenorrhea (no period)
• Breast tenderness
• Weight gain
• Acne
• Increased hair growth

Side effects of the progestin injection include:

• Irregular periods
• Loss of bone density

Risks

Serious side effects are rare, but they include:

• Menstrual bleeding that is unusually heavy or that lasts a long time
• Severe stomach pain
• Severe headaches

Combined estrogen and progestin oral contraceptives may increase the risk of getting breast cancer, endometrial cancer, and liver tumors. It is not known whether progestin-only (norethindrone) oral contraceptives also increase the risks of these conditions. 

A 2016 review of the use of progestin and breast cancer risk concluded that, unlike other oral contraceptives, studies indicate that progestin-only formulations do not increase the risk of breast cancer. The researchers noted that the six studies reviewed had small sample sizes, so larger-scale clinical studies are needed.

Advantages and Disadvantages of Progesterone-Only Birth Control Pills

Before You Start

Before you begin taking a progestin-only medication, your healthcare provider will want to assess your overall health. You should tell them if you take any other medications or supplements as well and if you smoke.

Your healthcare provider will advise you on when your chosen method will become effective against pregnancy. For example, the minipill needs to be taken for a week before it becomes effective. Therefore, you will need to use a barrier method of birth control if you are sexually active during that time.

An injectable will be immediately effective if it is given within the first seven days after your period has started; if it has been longer than that, you will need a backup method for the first week after the injection.

An IUD becomes effective immediately upon insertion.

Things to Keep in Mind

If you opt for the minipill, it is very important that you take it at the exact same time every day. The Depo-Provera shot must be given every four months. Another thing to consider before starting a progestin-only method is whether you hope to become pregnant in the future. Fertility returns right away after you discontinue some of these methods (such as the minipill), while it may take several months with others (such as the Depo-Provera injection).

Types of Progesterone-Only Birth Control

Progestin-only birth control comes in many different forms. Here's a rundown:

Birth Control Pills

As their name suggests, progestin-only birth control pills do not contain any estrogen. They are available in 28-day packs which you take every day during your four-week cycle. All 28 pills contain progestin; there are no placebo pills.

The minipill only comes in one formulation in the United States, called norethindrone. It comes in a generic form, or with brand names including:

• Camila
• Errin
• Heather
• Jolivette
• Micronor
• Nora-BE

Depo-Provera Injections

Depo-Provera is a birth control injection that slowly releases progestin medroxyprogesterone acetate into your body, providing protection from pregnancy from 11 to 14 weeks. If you opt to use Depo-Provera, you will need four injections each year. The injection also comes in a generic form.

Depo-Provera injections offer the added benefit of reducing the pain associated with endometriosis. 

Common side effects include weight gain, irregular bleeding, spotting, and prolonged bleeding. Once stopped, it may several months to a year to start ovulating again and become pregnant.

Mirena IUD

The Mirena IUD is an intrauterine device (IUD) that continuously releases a small amount of progestin for up to seven years; it is more than 99% effective at preventing pregnancy. The Mirena IUD has also been approved to help treat heavy periods.

The Mirena IUD is inserted by your healthcare provider and has strings that allow you to check that the device is still in place. As with all intrauterine devices, complications may include perforation of the uterus, infection, and accidental expulsion.

Skyla IUD

Skyla is another progestin-only IUD option. It is a bit smaller than Mirena and is typically easier for a healthcare provider to insert. Once inserted, the Skyla slowly releases a form of progestin (called levonorgestrel) over a three-year period.

The complications of use are the same as for the Mirena IUD, which may include uterine perforation, infection, and expulsion.

Nexplanon Subdermal Implant

Nexplanon is the newer version of the Implanon subdermal implant. This is a progestin-only birth control device that contains the progestin etonogestrel and consists of a flexible plastic implant about the size of a matchstick.

Nexplanon is inserted under the skin of the arm and can provide up to three years of pregnancy protection. Nexplanon is radiopaque, meaning that it can be seen in an X-ray. This helps your healthcare provider see if it has been properly placed. Insertion requires a local anesthetic and generally takes a few minutes.

After implantation, you may experience bruising, pain, itching, burning, numbness, bleeding, scarring, or infection at the insertion site.

Noristerat Injection

The Noristerat injection is a birth control delivery system containing progestin norethisterone enanthate. It is not available in the United States but is commonly used in the United Kingdom, Europe, Africa, and Central America.

The Noristerat injection is designed to be a short-term birth control method. Women may choose it after being immunized against rubella (to prevent pregnancy while the virus is active) or while awaiting their partner's vasectomy to become effective. The Noristerat injection will continuously release progestin into your system for up to eight weeks.

Which Type Is Right for You?

When deciding which form of progesterone-only birth control method to choose, you should take into account the convenience factor, among other things. Can you reliably take the minipill at the same time every day, or are you better off with the injection, IUD, or implant, which you don't have to think about for months or years?

Also, if you know if or when you might like to become pregnant, consider whether a method that is instantly reversible (the minipill, for example) is preferable to one that may not restore fertility for months once you stop it (such as the injection). The best way to make an informed decision is to discuss these pros and cons with your gynecologist.