Deep vein thrombosis and pulmonary embolism now affect up to 900,000 people in the United States each year and the numbers are still on the rise. Deep vein thrombosis is a blood clot that forms in the deep veins of your body, usually in lower extremities. The blood clot itself is not life-threatening, although it does become extremely painful the longer it blocks healthy blood circulation and affects vein valves. The problem is that when a blood clot forms in deep veins, it can break off and travel towards the lungs, where it blocks the blood flow and can potentially be fatal – a condition called pulmonary embolism.

There are various risk factors that contribute to developing a blood clot – genetic blood disorders, bed rest and immobilization, long traveling, smoking, excess weight, impaired blood flow, chronic venous insufficiency, etc. One of the risk factors is also a medication used by millions of women around the globe – oral contraceptive, or birth control pill. So what is it about birth control pill that can cause deep vein thrombosis, and potentially pulmonary embolism?

The answer is simple – the hormones. Birth control pills contain various levels of estrogen and progesterone – that’s why they’re called combination pills, and within time three groups of contraceptives have been developed: first-generation, second-generation and third-generation pills. Using these hormones might lead to changes in the blood that promote excessive clotting, or thrombosis, especially if other risk factors are involved as well (e.g. smoking, traveling on a long-haul flight, or immobilization after surgery). According to research and statistics, third-generation contraceptives pose higher risk of DVT than the previous generations. The reason behind this is that estrogen is the common ingredient in all generations of oral contraceptives, whereas the type of progesterone is different in each generation. Initially, estrogen was believed to increase the clot risk, and that’s why newer generations of contraceptives started using lower dose of estrogen. But now it’s turning out that it could actually be the type of progesterone that affects the clotting – hence the higher occurrence of DVT when using the newest, third-generation birth control pill.

The research on how much oral contraceptives affect blood clotting and what role they play as a DVT risk factor is still ongoing. One thing can be said with absolute certainty, though. If you suffer from or experience any other of the DVT risks already, the usage of oral contraceptives should be profoundly discussed with your physician and the benefits of birth control pill should be weighed against the possible risks – and those are definitely not trivial.