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How long after taking birth control pills might a blood clot form in high risk women like smokers?

Blood clots are possible complications of using birth control pills, especially for women at higher risk for blood clots; namely women who smoke, and women over age 35.

However, is there an answer to this question: How soon after taking birth control pills on a regular basis, can a blood clot develop in women at high risk?

For this article I consulted with Dr. Corinne Bazella, OB/GYN with University Hospitals Case Medical Center. She explains, “A blood clot can form anytime while on birth control in any patient.

However, it happens more often in the first years of use.  Blood clots form in the deep veins of the legs, and can travel to the lungs through the circulation, causing a life threatening condition called a pulmonary embolism.”

This kind of blood clot also goes by the name deep vein thrombosis, or DVT, and a woman on birth control increases the baseline risk of blood clots with birth control if she has any one of numerous risk factors.

Dr. Bazella lists the following additional risk factors for blood clots in women on birth control, but also for people in general:

  • Inherited clotting disorders
  • surgery
  • prolonged immobility (especially in cramped quarters such as on airplanes
  • inertia from excessive desk work or bed rest
  • trauma
  • obesity
  • smoking. If you’re a woman over age 35 who smokes, this puts you at considerable risk for blood clots while taking birth control pills that contain estrogen; avoid estrogen-containing birth control pills.

Ironically, a woman is much more likely to develop a blood clot while pregnant, than while on birth control pills.

Dr. Bazella explains, “In healthy nonsmoking women who are on combination low dose birth control pills, the risk of getting a blood clot is 12-20 women in 100,000.

This risk greatly increases with pregnancy and is as high as 48-60 women in 100,000.

Therefore, the risk of birth control pills causing a blood clot is less than the risk of getting a blood clot while pregnant, which is what you are trying to prevent!”

Dr. Bazella’s expertise includes abnormal uterine bleeding, adolescent gynecology, contraception and menopausal care.
Lorra Garrick has been covering medical, fitness and cybersecurity topics for many years, having written thousands of articles for print magazines and websites, including as a ghostwriter. She’s also a former ACE-certified personal trainer.