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| Deep-vein thrombosis and the pill |
| Discusses the influence of taking the 'pill' on your chance of having a blood clot. |
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Introduction and history
Does using the pill increase my chances of getting a blood clot?
Should I stop taking the pill?
Summary
References
Introduction and history
The combined oral contraceptive pill, or ‘pill’, is one of the most popular and effective methods of contraception. About 25% of women who have used contraception have relied on the pill at some point in their life. Taken properly, the pill is better than 99.9% effective in preventing pregnancy. This means that less than one pregnancy will occur among 1000 women using the pill for a year. The pill also helps to improve the quality of life and health of women, resulting in:
- shorter and lighter periods
- less period (menstrual) cramps or premenstrual symptoms
- reduced risk of cancer of the ovaries or womb
- reduced acne
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 | The pill contains a mixture of the hormones estrogen and progestogen. These hormones are similar to those that are naturally produced in women. There are many types of combined pills available and they differ according to the levels of hormones and the type of progestogen they contain.
When the pill was first introduced in the 1960s, the doses of the female hormones estrogen and progestogen were quite high. As a result of the high doses used, there were more reports of cardiovascular complications, such as heart attack, and blood clots in the legs and lungs. To reduce the risks of these side effects, new-generation pills were developed, which mixed lower doses of estrogen with a progestogen. However, these pills had a number of side effects similar to the effect of male hormones, such as oily skin, weight gain, and raised cholesterol levels, so a ‘third-generation’ pill was designed with lower doses of different progestogens to reduce these side effects.
The second- and third-generation pills are the two major classes of pill that are used by women today. Both classes of pill contain a type of estrogen called ethinylestradiol that is combined with progestogen. The difference between the second- and third-generation pills is the type of progestogen they contain: depending on side effects experienced, women can choose a pill with differing amounts of progestogen or estrogen.
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Does using the pill increase my chances of getting a blood clot?
Beginning in the mid-1990s, some studies indicated that the risk of a blood clot (also known as thrombosis), although extremely low, was slightly higher in women taking second- and third-generation pills compared with women who were not taking the pill. The most likely reason for the higher risk of blood clots is that the pill can sometimes cause changes in your body, affecting the way your blood clots. When we cut ourselves, a number of chemical reactions in the blood help to form a blood clot to seal the wound and stop the bleeding. The types of blood clots that are associated with using the pill occur in the deep veins of the legs or pelvis, and are known as deep-vein thrombosis (DVT) or venous thromboembolism (VTE).
It has been known since 1961 that there is a slightly higher risk of blood clots in women who use the pill. This higher risk depends on a number of factors, including the type of pill that is being used. The third-generation pills have recently been associated with a slightly higher risk of blood clots than the older-generation pills. For every 100,000 women who are not taking the pill, approximately 5–11 of them will develop a nonfatal blood clot in a year. Taking a second-generation pill increases this number to 15, and taking a third-generation pill increases it to 30. This higher risk of developing a blood clot is generally highest when you start taking the pill for the very first time and disappears soon after you stop the pill.
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Should I stop taking the pill?
Despite there being a slightly higher risk of developing blood clots for women taking the pill, blood clots are very rare, and the overall risk remains low. In fact, your risk of developing blood clots is higher if you are pregnant than if you are taking the second- or third-generation pill. If you are already taking a third-generation pill, there is no need for you to switch to another type of pill.
If you are taking the pill or are considering taking the pill, it is important to consider certain risk factors for developing a blood clot. If you have had a blood clot in the past or have a clotting disorder, you should avoid taking the pill. Women who have had a clotting disorder called thrombophilia from birth (caused by genetic defects such as Protein C or S deficiency, antithrombin deficiency or the factor V Leiden mutation), and are taking the pill, have a higher risk of developing blood clots and should be advised to use an alternative form of contraception. Alternative forms of contraception include barrier methods (e.g. diaphragms, or condoms for male partners) and an all-progestogen pill, which is associated with a very low risk of blood clots. However, because only a small proportion of women have thrombophilia, women who want to start taking the pill are not checked routinely for this disorder unless they have a positive family history or personal history of blood clots.
The risk of a blood clot may be increased by other factors that must also be considered before starting, or while taking, the pill. Some of the risk factors for a blood clot are:
- a previous blood clot
- a close family member who has had a blood clot
- being overweight
- smoking
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Although these risk factors do not prevent you from taking the pill, they need to be considered, especially if you have already been advised not to take other types of medication in the past.
It is not clear if women should stop taking the pill before having a major operation. The decision to stop the pill seems to be based on the balance between the small overall increased risk in women who use the pill and the risks associated with stopping the pill 4–6 weeks before surgery, such as unplanned or unwanted pregnancy. Women undergoing uncomplicated minor or intermediate procedures, such as diagnostic laparoscopy (an examination of the inside of the abdomen using a pencil-thin camera), do not need to stop taking the pill. Women at moderate risk of thrombosis should discuss the risks of stopping taking the pill with their doctor, and it may be decided that it is appropriate for them to stop the pill. For women that remain on the pill, methods may need to be used to prevent a blood clot from forming. For women having an emergency operation, the risk of developing a blood clot is increased, and medication to help prevent blood clots, such as low-molecular-weight heparin, should be considered.
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Summary
Although there is a slightly higher risk of blood clots in women who take the pill, the pill is widely used and remains a safe and effective method for preventing pregnancy.
If you do notice the symptoms of a blood clot, you should consult your doctor immediately. The symptoms of a blood clot may not be obvious, although some people may experience:
- swelling of one of the legs
- pain and tenderness of one of the legs
- redness of one of the legs
Sometimes a blood clot can move through the blood to the lungs, where it becomes lodged, which is known as a pulmonary embolism. In this case you may experience:
- shortness of breath
- sharp chest pain (that may be worse when breathing in)
- coughing up blood
- a rapid heart beat
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References
Oral Contraceptives – An update Chapter 2, Population Reports, Series A, Number 9. http://www.jhuccp.org/pr/a9/a9chap2.shtml
Burkman RT et al. Current perspectives on oral contraceptive use. American Journal of Obstetrics and Gynecology 2001;volume 185:pages S4–12.
Borgelt-Hansen L. Oral contraceptives: an update on health benefits and risks. Journal of the American Pharmaceutical Association 2001;volume 41:pages 875–86.
Kovacs P. The risk of cardiovascular disease with second- and third-generation oral contraceptives. Medscape Women's Health eJournal[TM] August 2002. www.medscape.com/viewarticle/439354
Greer IA et al. Problem-based Obstetrics and Gynaecology, Churchill Livingstone 2003, Chapter 4.
Koster T et al. Oral contraceptives and venous thromboembolism: a quantitative discussion of the uncertainties. Journal of Internal Medicine 1995;volume 238:pages 31–7.
Spitzer WO et al. Third generation oral contraceptives and risk of venous thromboembolic disorders: an international case-control study. Transnational Research Group on Oral Contraceptives and the Health of Young Women. British Medical Journal 1996;volume 312:pages 83–8.
Girolami A et al. Oral contraceptives and venous thromboembolism: which are the safest preparations available? Clinical and Applied Thrombosis/Hemostasis 2002;volume 8:pages 157–62.
Thromboembolic Risk Factors (THRIFT) Consensus Group. Risk of and prophylaxis for venous thromboembolism in hospital patients. British Medical Journal 1992;volume 305:pages 567–74.
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Quick answers to common questions about thrombosis and its treatment.
Go to the Common questions section
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An alphabetical list of the thrombosis-related terms used on this website. Go here if you want to learn about terms like 'aPTT test', 'LMWH' and 'osteoporosis'.
Go to the Encylopedia
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