Birth Control Pill Safety

birth_control_pills.jpgSome oral contraceptives increase the risk of blood clots more than others.

All estrogen-containing birth control pills increase the risk of blood clots for all women, but some types of contraception increase the risk more than others because of the progestin they contain.

The medical name for a blood clot in a vein is venous thrombosis. Most often, blood clots form in the legs or pelvic veins, but from there can break off and travel to the heart and then to the lungs. A blood clot that travels to the lungs is called a pulmonary embolism, which can be deadly, especially if not treated promptly.

Women who are obese, have diabetes or migraines, who smoke, who have heart disease risk factors such as high blood pressure, or who have a family history of blood clots are at a significantly higher risk of developing blood clots while taking oral contraceptives.

I have not included brand names of oral contraceptives because like a shell game, manufacturers of oral contraceptives are constantly changing the names, doses and contents of their birth control pills, perhaps to avoid being on a list like the one below. The packaging or information insert for all birth control pills will contain the name of the synthetic hormones in the pill, and the dose.

The list below is of the progestin part of the birth control pill. Most birth control pills are made of a synthetic estrogen and a synthetic progesterone, called a progestin. Research showed long ago that the higher the dose of estrogen in a birth control pill, the higher the risk of a blood clot. (This is not a straightforward comparison because some of the synthetic estrogens are more potent than others). Now we know that some progestins are more likely than others to contribute to the formation of a blood clot.

List of Birth Control Progestins and Risk of Stroke

The numbers below represent the odds of users having a blood clot compared to those who do not use birth control pills. Thus, the risk of blood clot for a woman using a birth control pill containing levonorgestrel is 3.6 times higher than for a woman not taking any birth control, and so on down the list.

Levonorgestrel                3.6
Norethisterone                3.9
Gestodene                         5.6
Lynestrenol                      5.6
Norgestimate                   5.9
Drospirenone                   6.3
Cyproterone acetate      6.8
Desogestrel                       7.3


Data comes from: van Hylckama Vlieg A, Helmerhorst FM, Vandenbroucke JP et al, “The venous thrombotic risk of oral contraceptives, effects of oestrogen dose and progestogen type: results of the MEGA case-control study,” BMJ 2009 339: b2921.


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