Hormonal Birth Control & Clotting

Know Your Risk. Recognize Symptoms.

Birth Control Options

A spectrum of family planning or birth control options exist and, while each may work somewhat differently, they are all designed with one goal in mind: To prevent pregnancy.

A woman’s preferred method of birth control may change over her lifetime and is influenced by many different factors, including:
  • Her age and health history
  • Her reproductive goals, such as the number of children she may want and how soon she wants to get pregnant

  • Relationship factors, including marital status, number of sexual partners, how often she has sex and partner preferences

To be effective, any method of contraception must be used consistently and correctly. Contraceptives that require little effort, such as IUDs, contraceptive implants and sterilization, are associated with lower pregnancy rates. In contrast, methods that require monitoring fertility or periodic abstinence are associated with higher pregnancy rates.

The best method of birth control for you is one that is safe, that you are comfortable using, and that you are able to use consistently and correctly.

Birth control or contraception options available to women today generally fall into these categories:

  • Barrier Methods: Condoms, diaphragms, cervical caps, contraceptive sponges
  • Short-acting hormonal methods: Birth control pills, patches, shots, vaginal rings, and emergency contraceptive pills used daily, weekly, or monthly.
  • Long-acting reversible contraception or long-acting hormonal methods: IUDs or devices which are implanted into the uterus and, depending on the device, kept in place for three to 10 years or until a decision is made to remove them.
  • Sterilization: Tubal ligation for women, vasectomy for men, permanently prevents someone from getting pregnant or from being able to get someone else pregnant.
  • Fertility awareness methods: Involve the monitoring of fertility, or the days during the month when a woman can get pregnant, often based on basal body temperature and cervical mucus.

Safety is a Priority

Effectiveness is, of course, one important factor to be considered when choosing birth control, but it’s also important to weigh this crucial benefit against any potential risks associated with the birth control method you might choose.

While hormonal birth control has been used safely by millions of women over the past six decades, as with any prescription medication it can cause side effects. Specifically, birth control methods that contain estrogen can increase a woman’s risk for dangerous blood clots.

Estrogen and synthetic progesterone (called progestin) are hormones commonly used in many forms of birth control (including the pill, patch, and ring). Estrogen-based contraception methods cause an increase in the level of clotting proteins in a woman’s body, which increases a woman’s risk for blood clots.

All too often, we hear stories of unsuspecting and otherwise healthy women of child-bearing age who are prescribed birth control that contains estrogen and who subsequently have experienced a blood clot or lost their life to a blood clot.

Blood clots are rare among women of child bearing age who are not using hormonal birth control: The rate of blood clots among women of child bearing age who are healthy, including women who are not taking hormonal birth control, is between one and five out of 10,000 women each year (U.S. FDA).

Woman looking at birth control pills

These various types of birth control work in different ways and may:

  • Prevent sperm from reaching the egg
  • Inactivate or damage sperm
  • Prevent an egg from being released each month
  • Alter the lining of the uterus so that a fertilized egg doesn’t attach to it
  • Thicken cervical mucus so that sperm can’t easily pass through it

Hormonal birth control methods increase a woman’s risk for blood clots: The rate of blood clots among women who are taking hormonal birth control is higher, or about three to nine out of every 10,000 women using hormonal birth control each year (U.S. FDA).

According to the National Center for Health Statistics, about 65 percent of the 72.2 million women in the U.S. aged 15-49 use some form of contraception:

  • Nearly 19 percent female sterilization
  • Nearly 13 percent birth control pills
  • A little more than 10 percent long-acting reversible contraceptives
  • Almost 9 percent male condom


  • Hormonal contraceptive pills carry a three- to nine-fold risk of blood clots compared to nonusers (U.S. FDA).

  • Hormonal vaginal rings and transdermal patches carry a six- to eight-fold risk for blood clots compared to nonusers (Lidegaard et al. 2012).

  • Obesity can double blood clot risks compared to normal weight (Sidney et al. 2004).

  • The use of hormonal birth control during the first year carries the greatest risk, especially in women under age thirty, where the risk increases thirteen-fold (Martinelli 1999, Lidegaard, Edstrom, and Kreiner 2002).

  • If a woman has a genetic clotting disorder such as factor V Leiden, her risk for clotting with the use of hormonal birth control increases four-fold (Vandenbroucke 1994).

Genetic Clotting Disorders Amplify Clotting Risks

Women sitting on couch learning about their genetics

Experts in hematology explain that genetic testing is not universally advised prior to starting combined hormonal contraception, except at times among women who have a genetic clotting disorder or thrombophilia(1), because their risk for developing a blood clot increases to 62-fold in the first year of hormonal contraceptive use and 25-fold after the first year(2). While studies have shown it is not effective to screen all women universally, selective genetic testing for women who are first-degree relatives of individuals with a history of clotting or known inherited clotting disorder has shown to be more cost effective than universal screening among all women and it also might provide important guidance about contraceptive choice(3). More recent research involving a patient-centered review of the issues that surround genetic testing relative to combined hormonal contraceptives outlined the current complexities confronted in this space, and demonstrated how the benefits of genetic testing leverage or outweigh many previously stated concerns among healthcare professionals, policymakers, and the public. In fact, this 2019 study, Re-Examining Genetic Screening and Oral Contraceptives: A Patient-Centered Review(4), advocates for 1) a more patient-centered approach relative to genetic testing for thrombophilia when contraceptive options are being considered 2) improved understanding and education of both physicians and patients about the implications of thrombophilia screening and 3) the opportunity for women to access thrombophilia testing as part of the contraceptive decision-making process.


  1. Ann Med Interne (Paris), 2003 Sep-Oct;154(5-6):279-82
  2. Thromb Res. 2016 May:141:153-7, Duration of oral contraceptive use and the risk of venous thromboemolism. A case-control study. Martinelli et al.
  3. Br J Haematol. 2005 Oct:131(1):80-90. Screening for thrombophilia in high-risk situations: a meta-analysis and cost-effectiveness analysis. Wu et al.
  4. J Pers Med 2019 Mar; 9(1): 4 Re-Examining Genetic Screening and Oral Contraceptives: A Patient Centered Review, Hiedermann et al.

Reduce Your Risk

If you find that you are at increased risk for blood clots, or choose to avoid the increased risk for clotting associated with hormonal birth control, there are optional birth control methods that can be used safely and effectively, including:

Contraception is a personal choice, and should be made with a full understanding of the benefits and risks associated with any method of birth control a woman may choose. It’s important for women to thoroughly research all birth control options and discuss those options with their healthcare provider to determine which birth control method best meets their needs in terms of both effectiveness and safety.