The Pill and Thrombosis
Deep vein thrombosis (DVT) is a blood clot that forms in one of your deep veins, often happening in the leg
Your risk of getting DVT is slightly increased if you take the combined contraceptive pill, if you are pregnant or if you have been staying still for a long time or are overweight
Symptoms of DVT include pain or tenderness in one or both of your legs, swelling or a heavy aching feeling in your leg
Blood thinners are the most common DVT treatment
Drinking plenty of water, not drinking too much alcohol, trying to move your legs and wearing elastic compression stockings are ways of reducing your chances of DVT
Deep vein thrombosis (DVT) is a blood clot that forms in one of your deep veins, also known as venous thrombosis. It often happens in the deep veins of the leg. Because of the hormones in the pill, which make blood clotting easier, your risk of getting DVT is slightly increased if you take the combined contraceptive pill.
What is deep vein thrombosis (DVT)?
Deep vein thrombosis is the name for a blood clot that develops inside a larger vein – usually a vein deep within your lower leg or sometimes your thigh. A DVT happens to around one in every 1,000 people in the UK, and it can be dangerous because sometimes part of the clot breaks up and travels up to the lungs. If this happens it can potentially cause organ damage and even death.
What are the symptoms of DVT?
In some cases there are no symptoms. If you experience any of these symptoms, especially if they happen suddenly, get medical advice immediately.
- Pain or tenderness in one or both of your legs, which you might only feel when you’re standing or walking
- Swelling in one or both of your legs
- A feeling of warmth in the skin on your leg
- Red or discoloured skin on your leg
- A heavy aching feeling in your leg
If you experience sudden coughing (where you may bring up blood) breathlessness or rapid breathing; a sharp pain in your chest or become severely lightheaded, it could be a pulmonary embolism. Call 999 immediately or get to the closest A&E department.
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What can DVT be caused by?
DVT can be a result of many things. Anything that affects your blood clotting system, prevents your blood from circulating properly, or damages the walls of your blood vessels is a risk factor. The more risk factors you have, the more likely you are to develop a DVT.
Staying still for a long time is a known risk factor, so a long stay in hospital or being unable to move will increase your risk. Sitting for a long time on a long journey can also increase your risk. If your legs are still for a long time, your calf muscles don’t contract to circulate blood around your body.
Pregnancy increases the risk of developing a blood clot, especially in women who have an inherited clotting disorder. The risk of developing pregnancy-related DVT is highest up to six weeks after the birth of your baby.
Combined contraceptive pills and hormone replacement therapy (HRT) can affect your blood’s clotting ability.
Being overweight or obese increases the pressure in the veins, potentially putting you at a higher risk. Smoking can affect your circulation and blood clotting ability so being a smoker also increases your risk.
Being over the of age 60 to 65 increases your risk, even though a DVT can happen at any age.
Suffering from cancer, heart failure, severe infections, certain blood clotting disorders or dehydration, or having a previous DVT or a family member with thrombosis are among other risk factors for DVT.
What is the link between DVT and the contraceptive pill?
It’s been known for some time that the combined oral contraceptive pill is linked to a risk of DVT. Studies have found that women using any combined contraceptive pill has approximately three times the risk of developing a blood clot compared with non-pregnant women who aren’t taking the pill - although the risk is still very small.
Studies have also found that the risk is higher with some ‘third generation’ pills. The most commonly prescribed pills, which contain a hormone called levonorgestrel, increase the risk of DVT the least - only approximately six extra cases for every 10,000 women taking it per year of use.
The risk of DVT doubled for women taking pills containing the hormones desogestrel, gestodene, drospirenone, and cyproterone, compared with those containing levonorgestrel. These are often used to treat symptoms like acne and doctors don’t tend to prescribe them as a first choice contraceptive.
How is DVT treated?
You might be advised to keep your legs raised whenever you’re resting and you will likely be prescribed medication that stops the clot from damaging your body.
Blood thinners, or anticoagulants, are the most common DVT treatment, and stop a clot from growing or breaking off. They don’t actually thin the blood, despite the name, and they can’t dissolve a clot that’s already formed.
If you can’t be prescribed anticoagulant therapy, your doctor may discuss an Inferior Vena Cava (IVC) filter with you, which is a mechanical way of treating blood clots.
Your doctor may give you another type of drug called a thrombolytic agent if the clot is large or manually remove the clot (thrombectomy), if you have a pulmonary embolism or the DVT is in your arm rather than your leg. These treatments have to be carried out in hospital as there are some risks involved however other anticoagulation therapy can often be given at home.
How can you reduce your chances of DVT?
Changes in lifestyle can cut your risk factors for DVT. In particular, losing weight if you are overweight or obese, and quitting smoking if you are a smoker.
Travelling long distances raises your risk of DVT so any journey where you have to sit still for a long time can be a factor. If you are already at risk of DVT or have had it before, ask your doctor for advice before you travel.
In general, for any long journey you can help reduce your risk by:
- drinking plenty of water
- not drinking too much alcohol
- avoiding sleeping pills if you can, which can make you immobile
- trying to move your legs - flexing your ankles for example, and taking a short walk if you can
- wearing elastic compression stockings, providing you don’t suffer with conditions like peripheral vascular disease, current DVT, or leg ulcers
Dr Clair Grainger
Dr Clair Grainger studied at The University of Edinburgh from 2004 to 2009. She's worked in hospitals throughout Edinburgh and London before completing her GP training in North Middlesex Hospital in 2017.Meet our doctors
Last reviewed: 08 Mar 2019
DVT (deep vein thrombosis), National Health Service [accessed February 2023]
Combined hormonal contraceptives and venous thromboembolism: review confirms risk is small, GOV.UK [accessed February 2023]
Deep vein thrombosis (DVT), Mayo Foundation for Medical Education and Research (MFMER) [accessed February 2023]
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