Deep vein thrombosis (DVT) is something that happens when a blood clots form in the lower leg. This can be a possible serious side effect of taking the combined contraceptive pill. Before taking the pill, your doctor will make sure it’s suitable for you, ensuring you don’t have any underlying conditions that can increase your risk of a blood clot.

What is deep vein thrombosis? 

Deep vein thrombosis is the medical term for a blood clot in your leg. This usually occurs in the lower leg within the large vein running down the length of your leg. DVT (deep vein thrombosis) might also be known as venous thrombosis. Blood clotting is something that generally happens when wounded; the blood clots to prevent the body from losing too much. If there is no injury and the blood clot forms within a vein or artery, this blocks it and restricts blood flow.

What are the symptoms of deep vein thrombosis?

Deep vein thrombosis causes: 

  • Swelling and pain in one leg- usually the calf area
  • Tenderness 
  • A heavy, aching feeling in your leg
  • Warm skin around the affected area
  • Red skin below the back of the knee

A blood clot does not always cause symptoms. If it does, the pain in your leg will be worse if you flex your foot. While it usually only affects one leg, it can occur in both. 

What causes deep vein thrombosis? 

DVT doesn’t always have a defined cause, but the following circumstances put you at risk: 

  • Inactivity- for example due to injury, long-distance travel or hospital treatment
  • Damage to blood vessels- this can happen due to vasculitis, varicose veins and chemotherapy 
  • Cancer
  • Heart disease 
  • Hepatitis 
  • Arthritis or other inflammatory conditions 
  • Thrombophilia 
  • Antiphospholipid syndrome
  • Pregnancy
  • Hormonal treatments containing oestrogen 
  • A family history of the condition 

How is DVT treated? 

If you have a blood clot, this is treated with anticoagulation medications. Often referred to as blood thinners, they work by preventing the blood clot from growing and breaking off and blocking another part of your bloodstream. 

A medicine called Heparin is likely to be prescribed first to have an immediate effect. Warfarin is given to stop another blood clot from forming. Other medications include Rivaroxaban and Apixaban. 

If these medications have been ineffective or are unsuitable, another option is having Inferior vena cava filters. These are inserted into the vein to help filter the blood. 

Things you can do yourself include: 

  • Wearing compression stockings 
  • Regular exercise or movement 
  • Raising your leg to stop blood pooling in your lower body

What happens if I have a blood clot? 

If you have deep vein thrombosis, this can lead to further complications which include a pulmonary embolism or post-thrombotic syndrome. 

A pulmonary embolism is a severe condition that can be fatal. This is where a piece of the blood clot breaks off and travels to the lungs, blocking the blood vessels. It might cause difficulty breathing and chest pain, but it can also result in a collapsed lung or heart failure. 1 in 10 people will experience this complication. 

Post-thrombotic syndrome is less serious and causes long term symptoms in your calf after DVT. These include swelling, pain, rash and ulcers and affects roughly 30% of people who have DVT. People who are overweight or had a blood clot in their thigh are more likely to get these continued symptoms. 

How does the pill cause deep vein thrombosis? 

The combined pill doesn’t cause DVT but taking it increases your risk of experiencing it. This is because of the hormone oestrogen, which the pill contains; it causes the blood to clot easier. The progestogen-only (or mini pill) does not pose this risk as it doesn’t contain oestrogen. Studies indicate that taking the combined pill triples your risk of experiencing a blood clot in comparison with women not taking the pill. 

This may sound alarming, but the risk is still small, and blood clots are rare. Before being prescribed the pill, your doctor will assess your medical history to ensure that you do not have any other risk factors. Any previous history of blood clots or heart problems, or if you have mobility issues which mean you are off your feet a lot, means you should not take the combined pill. If this happens, the mini pill can be prescribed instead. 

What should I look out for if I am on the pill? 

Every woman who is prescribed with the combined pill should carefully read the information leaflet provided with it. This contains detailed information about blood clots, what the warning signs are and circumstances which means your doctor should be monitoring you closely. All women on the pill should have their blood pressure regularly monitored, at least once a year. Common symptoms are: 

  • A heavy feeling in one leg 
  • Pain, swelling and tenderness in the leg
  • Warmth of the skin where the blood clot is 
  • Red or blue skin discolouration 

The combined pill is not suitable for women who: 

  • Smoke and are over 35
  • Are obese 
  • Take certain medications 
  • Have a history of blood clots
  • Have a family history of blood clots 
  • Have ever had a stroke 
  • Have high blood pressure
  • Have heart problems 
  • Get severe migraines 
  • Have a history of breast cancer 
  • Have a history of liver disease 
  • Have a history of gallbladder disease 
  • Have diabetes with complications 

How can I prevent deep vein thrombosis? 

There are steps you can take to keep your risk of blood clots to a minimum. For example: 

  • Stop taking the pill, or hormone therapy, up to 4 weeks before being admitted to hospital 
  • Wear compression stockings where necessary 
  • Quit smoking 
  • Drink enough water, especially when travelling 
  • Avoid alcohol and sleeping tablets during long journeys
  • Move around and stretch your legs when you can while travelling 
  • Eat a healthy diet 
  • Exercise regularly 
  • Maintain a healthy weight 

Is the pill safe to take? 

While the combined pill does increase your risk of a blood clot, this risk is still rare; affecting 1 in 1,000 women. If you have ever experienced DVT in the past, then your risk will be higher, and it is advised not to take the pill if this applies to you. Health officials advise that the benefits of the pill outweigh the risks and that it is safe for most women to use. If you feel worried about this at all, then there is always the option of the progestogen-only pill, the implant, injection or hormonal IUS. There is also the copper IUD which is a non-hormonal contraceptive. 

It has also been reported that the DVT risk presented by the contraceptive patch is higher than the pill as the oestrogen content is 60% higher. However, the patch is designed to slowly release the hormones over seven days, as opposed to the pill, which comes as a daily dose. 


NHS > Deep Vein Thrombosis
Web MD > Birth Control Methods and the Risk of Blood Clots
NHS > Combined Contraceptive Pills 'Increase Risk of Blood Clots'
National Blood Clot Alliance > Is It True That Birth Control Pills Cause Blood Clots?
NHS > Combined Pill