Medical Questions » Contraception Questions » Question No. 222
| Question: | How does the birth control pill cause thrombotic problems? |
| Answer: | One of the rare side effects of taking the oral contraceptive pill is the development of a blood clot (thrombus) in a vein. This is now a very rare complication with the low dose pills that doctors have available.
If a blood clot does occur, it is usually in the veins in the calf. This causes considerable pain and tenderness of that part of the leg, and most patients would present to doctors with these symptoms for treatment.
If the clot is not treated early, it is possible for the clot to break away from the wall of the vein, and travel up the vein, through the heart and lodge in the lung. The effect this will have depends on the size of the clot, but it will block an artery in the lung, and the part of the lung affected will then die. If this is a very small area, the patient will have no serious problem, but if a major artery is blocked by a large clot, the result may rarely be fatal.
The thrombus (clot) forms because the hormones in the pill slightly alter the clotting factors in the blood, so that a minor injury to the vein (eg. repeatedly pushing back a chair with your calf as you stand) may be enough to start a clot in the blood.
Treatment involves medication to prevent the spread of the clot or further clot formation, and women who have such a problem should not use the contraceptive pill.
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