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Double myth: The contraceptive pill is harmless / The contraceptive pill causes thrombosis

Double myth: The contraceptive pill is harmless / The contraceptive pill causes thrombosis

Photographer:Fotograaf: Joey Roberts

Myth busters

“I don't want to scare you,” says Hugo ten Cate, professor of Clinical Thrombosis and Haemostasis, every time he gives a lecture on the relation between the contraceptive pill and thrombosis to third-year medical students. “About 70 per cent of our students are female, the majority of whom are on the pill. It is not just great as a contraceptive but also as a means to regulate periods. So, I am not arguing against its use, but it is not completely harmless. In a very small group, the use of the pill increases the chances of thrombosis.”

Ten Cate picks up a notepad and rapidly draws a few diagrams. “Chances of thrombosis are on average one in a thousand. Chances increase as one gets older, most patients are over sixty. In young women between 18 and 25, the risk is small: one in ten thousand. If they use the pill, the chance is slightly greater: six in ten thousand. So, it is a very low percentage, but because there are so many pill users, the absolute number is still considerable.”

Neither of the two statements ‘The contraceptive pill is harmless / The contraceptive pill causes thrombosis’ is true, but brushing them aside is not a good idea either. “In recent weeks, five young women between the ages of 16 and 36 came to the outpatients' clinic with a pulmonary embolism. This is when important pulmonary veins are blocked by a blood clot that causes chest pains, shortness of breath, and fatigue. The only risk factor that I could discover, was their use of the pill. The oldest of the five had being having problems for three weeks, had been to a physiotherapist, and her GP had advised her to ease up on sports. In young people, GPs tend to relate these kinds of complaints to a pulled muscle, asthma, or a minor case of pneumonia. There is nothing to see on the outside.”

It would be pointless to screen every female for higher susceptibility.  “Then you would have to test eight thousand women to find one. That is not cost-effective.” Ten Cate does argue for greater awareness, both among doctors and among women themselves. “If you show any symptoms, go to your GP and present this as a possibility, is what I say to my students. With a simple test, the GP can check if there is a real risk of thrombosis.”

Anyone who has had thrombosis caused by the contraceptive pill, would be best off not using this type of contraceptive.  “An IUD is an option, even the Mirena IUD, which contains a small amount of hormone. This has no effect on blood clotting; it does say so on the information leaflet, but this is incorrect.”


Thrombosis and strokes

Recognise thrombosis and save lives. That is the motto of the afternoon organised by MUMC+ on Friday 13 October within the framework of World Thrombosis Day. In addition to various lectures by scientists on topics such as thrombosis and strokes, and thrombosis and pulmonary embolism, a patient will be interviewed. For more information: and

Mythbusters is a series in which academics shoot down popular myths on complex topics



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