Pharmacotherapy Newsletter

Volume 1, Issue 12, 04/06/2009

Question

How do oral contraceptives (birth control pill) increase clotting factors and subsequently increase the risk for developing venous thromboembolism (DVT and/or pulmonary embolism (PE))?

Answer

The use of combined oral contraceptives (containing estrogen and progesterone) is common across the world.  Unfortunately, their use has resulted in considerable adverse drug events that have caused much debate about their safety in the general population.  One such adverse drug event that dates back to the early 1960's is the development of venous thromboembolism (VTE), which includes both deep vein thrombosis (DVT) and pulmonary embolism (PE).^1-7  It has been estimated that the annual incidence of venous thromboembolism (VTE) in women of child bearing age who are not taking oral contraceptives is 1 in 10,000.⁸  The incidence is increased 3-5 fold when women of child bearing age use estrogen containing oral contraceptives.⁹  This risk is even greater in patients taking higher doses of estrogen, those with an underlying hypercoaguable disorder, such as factor V Leiden, and in patients taking third generation oral contraceptives containing desogestrel, gestodene, or norgestimate.^2-7,9-17  So, how do estrogen containing oral contraceptives increase the risk for VTE?