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One of the most popular methods of hormonal contraception is ‘’the pill’’, which uses the regulation of female sex hormones to prevent pregnancy. For the combined pill, this typically involves combined synthetic variation of oestrogen and progesterone. While the pill is 99% effective at preventing pregnancy, it does come with some risks, one of which is a blood clot.
There is an established link between hormonal contraceptives and blood clots, but the risk is not the same for everyone. The risk of thrombosis (blood clots) is dose and type of contraception dependent, and it increases with age, congenital and acquired predisposition to thrombosis.
The first thing to note is that oral contraception does not directly cause blood clots, however it does increase the risk of the occurrence, especially in women who are predisposed to them. A hereditary disorder that predisposes adults to blood clots is known as thrombophilia, and women who are affected by it are at an increased risk of developing blood clots from hormonal contraception. Regardless of your family history, you’re also at a higher risk if you’ve suffered a blood clot at any point in the past. If you have thrombophilia, you should talk to your doctor about which oral contraceptives are right for you and your unique circumstances.
The exact mechanism by which oral contraceptives increase the risk of blood clots is not fully understood, but it is thought that the hormones in the pills may play a role in blood coagulation that leads to blood clots.
Combined contraceptive pills contain synthetic oestrogen and progestogen, of which oestrogen is thought to be the main culprit of increased thrombosis risk. This risk increase is also observed in pregnant women, regardless of medical history, who have an average of five times the blood clot risk during pregnancy.
Pre-existing conditions are one of the main risk factors when it comes to blood clots, closely followed by the acquired risks.
Some blood clot risks you will be able to mitigate through lifestyle adjustments, diet and exercise, while others are simply out of your control. If this is the case for you, explore the alternate forms of contraception, especially if the blood clot risk is high.
Below are the blood clot risk estimates with and without hormonal contraception, based on lifestyle and genetic predispositions.
|Risk factor||Risk estimate||Risk estimate in combination with COCs||Prevention recommendations|
(more than 4 hours)
|2–4 times||14–20 times||Keep hydrated; frequent exercise of leg muscles; compression stockings|
|Trauma/surgery||2–5 times||5–12.5 times||Discontinue COCs for 4 to 6 weeks before surgery or after traumatic injury|
|Obesity||1.7–2.4 times||10–24 times||Weight loss|
|Smoking||1.4–3.3 times||8.8 times||Smoking cessation or decreased use|
|Factor V Leiden||4–8 times||28–35 times||Choose a different type of contraceptive|
|Prothrombin G20210A||2–3 times||16 times||Choose a different type of contraceptive|
There is generally a low probability of deep vein thrombosis in healthy women with no risk or family history. The risk increases with age, especially for women over 35, and with additional risk factors, such as the presence of cardiovascular disease, obesity, fracture, renal disease, and both congenital and acquired thrombophilic disorders. These risk factors are not rare.
Blood clots are a serious medical condition that can lead to potentially life-threatening complications if they turn into an embolism, so it’s important to be aware of the signs and symptoms.
While they can occur without any warning signs, there are some common symptoms that may be an indication that a blood clot is forming or has already formed. These include, but are not limited to:
IMPORTANT: If you experience any of these symptoms, seek medical attention immediately. Recognising the signs of a blood clot is essential for prompt treatment and prevention of serious complications, such as the thromboembolism or pulmonary embolism, which can be life-threatening.
Blood clots can be diagnosed through a physical examination and a series of tests, including an ultrasound or MRI. Treatment typically involves anticoagulant medication to break up the clot and prevent it from causing further damage, such as detaching itself from the main site and travelling to the brain or lungs. In severe cases, surgery may be necessary to remove the clot.
Some blood clotting risk factors are out of your control, however there are many other actions that can be taken to reduce the likelihood of a blood clot forming. Even if you’ve never had a blood clot before and aren’t at a higher risk, blood clots can still occur in certain conditions. Here are some things you can do right now to reduce the risk of blood clots:
Weight management is essential in reducing the risks of blood clots when using combined contraceptives, as well as lowering other general health risks.
If you’re at a high risk of blood clots or are worried about them, a change in the birth control method you use can mitigate this risk.
Look for the oral contraceptives that do not have any oestrogen present, such as the mini pill. Studies are ongoing regarding progesterone and blood clots, though current research shows no evidence of the increase in blood clots when administered orally. Transdermal, vaginal, or intrauterine hormonal contraceptives and injectable progestins require further study.
|Blood clot risk of women using a combined hormonal contraceptive|
|Containing:||Brand examples:||Risk (approximately):|
|Levonorgestrel||Loette, Microgynon||0.05 - 0.07% of women|
|Norethisterone||Activelle, Synfase, Novofem,|
|Etonogestrel||NuvaRing, SyreniRing||0.06 - 0.12% of women|
|Drospirenone||Yaz, Yasmin, Eloine||0.09 -0.12% of women|
|Desogestrel||Mercilon, Marvelon, Gedarel,|
|Gestodene||Akizza, Femodette, Sunya, Millinette, Katya, Femodene||0.11% of women|
For reference, 2 out of 10.000 women (0.02%) who are not using a combined hormonal contraceptive pill/ring/patch, and are not pregnant, are at risk of getting a blood clot each year.
To mitigate the risk of these completely, consider non-hormonal birth control such as barrier protection (condoms) or the copper intrauterine device (IUD), as these can offer protection against pregnancy without the use of any hormones. If you are already at a high risk, these might be a better alternative for you.
This is why it’s important to be completely honest with your doctor or your healthcare provider about your conditions and lifestyle, as they will be able to recommend the most suitable alternative contraceptive method for you, with minimal risk of any side effects that could impact your general health, and with maximum efficiency in pregnancy protection.
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