Topic Overview

In some women, the estrogen in combination hormonal birth control methods increases the risk of a blood clot in a leg (deep vein thrombosis, or DVT) or a blood clot in a lung (pulmonary embolism, or PE). A blood clot in a leg vein can travel through the circulation system and cause pulmonary embolism.

The risk for DVT or PE is overall very low with hormonal contraceptives. In the past, combination birth control pills contained a higher dose of estrogen, which increased the risk of DVT and PE. Now the combination pill contains a lower dose of estrogen, and the risk is reduced. The risk for DVT or PE is actually higher for a pregnant women than for non-pregnant women taking hormonal contraceptives.

Combination hormonal birth control pills that contain the progestin called desogestrel increase the risk of blood clots more than birth control pills that contain other types of progestin.^{footnote 1} The progestin called drospirenone (found in pills such as YAZ or Yasmin) also might have a greater risk of blood clots than other types of progestin.^{footnote 2} Talk to your doctor about the risk of blood clots when deciding which pill is right for you.

The birth control patch delivers more estrogen than the low-dose birth control pills do. Health Canada warns that women using the patch are slightly more likely to get dangerous blood clots in the legs and lungs than women using birth control pills. So talk to your doctor about your risks before using the patch.

The known risk factors for blood clots (DVT or PE) include:^{footnote 3}

• Pregnancy and the first 6 weeks after delivery.
• Personal or family history of blood clots.
• Obesity.
• Surgery. Birth control pills are usually stopped within 1 month of major surgery to decrease the risk of a blood clot. The risk needs to be balanced against the risk of an unintended pregnancy by stopping the pills.
• Coagulation disorders, such as factor V Leiden mutation. This is a genetic blood clotting problem.
• Inactivity, such as during long distance travel in cars or airplanes.

Studies have shown that high blood pressure, diabetes, and superficial varicose veins do not increase the risk for blood clots.^{footnote 3}