What to know about birth control and blood clots

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Most birth control uses hormones to control the menstrual cycle and help prevent ovulation. Some help prevent fertilized eggs from implanting.

They usually contain a combination of estrogen and progestin, which is a synthetic form of progesterone. Some birth control only contains progestin. Certain hormones may make the blood clot more easily. Some examples of hormonal birth control include:

• hormonal IUDs
• hormonal birth control pills
• hormonal implants

The absolute risk of blood clots is still low. The National Blood Clot Alliance reports that about 1 in 3,000 women taking birth control will get a blood clot in a year.

Although estrogen does not cause blood clots, it does increase blood’s ability to clot.

Some birth control only contains progestin. Most, but not all, research suggests that progestin-only birth control does not increase the risk of blood clots. But very high doses of progestin may increase a person’s risk. People with abnormal uterine bleeding usually receive these very high doses.

Newer third- and fourth-generation birth control pills such as Mircette, Yaz, and Yasmine use these newer progestin hormones, drospirenone or desogestrel, combined with ethinyl estradiol. Research shows they may increase a person’s blood clot risk even more than their first- and second-generation counterparts.

In 2012, the Food and Drug Administration (FDA) issued an advisory suggesting that contraceptive pills containing drospirenone may increase the risk of blood clots up to threefold.

Any birth control containing hormones can increase a person’s risk for blood clots.

While estrogen is known to increase the blood clot risk, the role of progesterone in blood clots is less significant. Some studies have found no connection at all.

This suggests that it may be safer to take progesterone-only types of birth control.

A 2012 meta-analysis looked at the risks of blood clots with various types of birth control.

It found that:

• progestin-only birth control pills did not significantly increase the risk of blood clots
• Mirena, a progestin-only IUD, did not significantly increase blood clot risk
• progestin injections, such as Depo-Provera, may increase blood clot risk

People with an increased risk for developing a blood clot, or who have had one before, should use a progestin-only option when choosing hormonal birth control. People who should not use contraception containing estrogen include:

• people with hypertension
• tobacco smokers over 35 years of age
• people with a history of venous thromboembolism (VTE)
• people with diabetes mellitus complications
• people with coronary artery disease
• people with migraine with an aura

A DVT is a type of blood clot that forms in deep veins, usually in one of the legs. It is a type of VTE.

Depending on the severity, it can either partially or fully block blood flow. If some of this blood clot breaks off and moves, such as to the heart or lungs, it can be very dangerous. A pulmonary embolism typically happens when a piece of DVT moves to the arteries that go to the lungs.

Although DVT is dangerous, it is also treatable when identified quickly. This is why it is important to know the signs of a DVT and be aware of the risk factors.

Birth control users are more vulnerable to DVT if they:

• are 35 years of age or older
• do not move for a long period of time, such as on a long flight or after surgery
• have experienced an injury to the legs, such as a broken bone
• have other cardiovascular health risk factors such as high blood pressure, diabetes mellitus, or obesity
• have certain genetic risk factors, such as genetic blood clotting disorders
• have cancer, a serious infection, or an autoimmune disease such as lupus

Sometimes, a person may mistake a blood clot for a calf injury or bruise. People who have other risk factors such as the ones listed above should carefully monitor these injuries, as they may be something more serious.

If they get worse or do not go away, a blood clot may be the cause.

The most common symptoms of a blood clot in the leg include:

• pain in one leg, especially when walking
• swelling in just one leg or foot
• redness, warmth, and tenderness around a painful area in the leg

If the clot breaks loose and flows away from the site of the DVT, it can lead to chest pain, breathlessness, fainting, coughing, or very low blood pressure. If a person experiences these symptoms, they should seek medical attention right away.

Learn more about DVT.

Estimates of the prevalence of blood clots caused by birth control vary. This is because, over time, studies have researched different types of birth control using different methods.

It is clear that the hormones in a particular contraception can play a role, as well as a person’s individual risk factors.

Combined contraception

One 2015 study gathered data on combined birth control (containing both estrogen and progestin) users in the United Kingdom. Researchers found a rate of around 6 cases of VTE blood clots per 10,000 women per year. This means that for every 10,000 women who use birth control for a year, there would be an annual average of 6 cases where this type of blood clot occurred.

Progestin-only contraception

There is less research on progestin-only birth control. While it is generally considered a safer option for people with certain risk factors, it can still cause a higher risk of blood clots. According to a paper published in the Journal of Community Hospital Internal Medicine Perspectives, nonhormonal birth control is the only safe option for certain people who are at high risk for VTE.

Third- and fourth-generation contraception

The risk of blood clots may be higher in people who use newer combined contraceptives containing desogestrel, gestodene, or drospirenone. Some of these birth control pills include Yaz, Yasmin, Safyral, Mircette, and Beyaz.

The American College of Obstetricians and Gynecologists (ACOG) committee echoes these concerns about some of the newer pills. But they also emphasize that some studies linking newer combined contraceptives to a higher risk of blood clots were somewhat flawed.

While the data on blood clots varies, the absolute risk remains low. People who are concerned about blood clots, have had one before, or have some of the risk factors listed above may prefer to use a nonhormonal form of birth control.

Some options for nonhormonal birth control include:

• Sterilization: This means a tubal ligation (“tying the tubes”) for females or a vasectomy for men.
• Condoms: These also protect against sexually transmitted infections.
• Diaphragms: These rest over the cervix. They contain spermicide to help prevent pregnancy.
• Nonhormonal intrauterine device (IUD): This type of IUD is a long-term birth control option, usually made of copper, which can last for years.
• Fertility awareness: This involves tracking one’s menstrual cycle to determine when a person is most fertile, then avoiding sex at those times.

Learn more about nonhormonal birth control options.

Although some forms of contraception increase a person’s risk for developing a blood clot, the absolute risk is still low. For example, the risk is much higher during pregnancy. The Centers for Disease Control and Prevention (CDC) estimate that pregnancy increases the risk for blood clots about fivefold.

Understanding a person’s individual risk factors, as well as knowing the warning signs of a blood clot, is important for people choosing to use hormonal contraception.

People who want to reduce their risk should consider either progestin-only or nonhormonal contraception.

Additionally, they should be mindful that some third- and fourth-generation pills such as Yaz have been linked to even higher blood clot risks.

A doctor can help a person choose the right birth control option for their individual needs.