Can birth control cause blood clots?

Reviewed by our clinical team

If you’re taking birth control or thinking of taking it you might be worried about side effects, including the risk of blood clots. Although the risk of developing a blood clot while taking contraceptives is low, there are factors that can heighten your risk. In this article we'll discuss contraceptives and blood clots, blood clot symptoms to look out for and the risk associated with contraceptive pills. 

What are blood clots?

Blood clots are clumps of blood that form in response to injury. This a natural and protective process by the body which helps to stop bleeding – if our blood couldn’t clot, we’d bleed excessively from the tiniest of scratches.

Most of the time, clotting happens as a safe, natural, and protective response to injury. Sometimes, however, blood clots form without an injury and fail to dissolve, causing blockages in the veins or arteries. A blood clot that forms in a vein, usually in the lower leg, is known as deep vein thrombosis (DVT). If these blockages travel to the heart, lungs, or brain they can cause serious issues such as pulmonary embolism, heart attacks and strokes.

The good news is that if you’re young and healthy, your risk of blood clots is really low. It’s also worth bearing in mind that blood clots can be successfully treated if they’re caught in time. Doctors can also prescribe blood thinning medication if they think you might be at risk.

What are the causes of blood clots?

There are a few different reasons why blood clots might form, including:

• Immobility - not moving around slows down blood flow, making clots more likely to form. Wheelchair users, people who have had surgery or in intensive care, or who have a leg in a cast, are more at risk of blood clots because they can’t move around. 
• Travel - There’s also an increased risk of blood clots associated with travelling long distances by plane, train, coach or car.
• Pregnancy - pregnant women are five times more likely to have a blood clot compared to women who aren’t pregnant. 
• Being overweight - losing weight can help you to avoid blood clots. 
• Routine medications - such as combined hormonal contraceptives and hormone replacement therapy (HRT)
• Medical treatments -  carry a slightly higher risk of developing blood clots e.g. chemotherapy

Blood clotting from birth control

The risk of blood clots in people using combined hormonal contraceptives is three times higher than in people who don’t use them. In 2014, the European Medicines Agency reported that they would expect between five and 12 people in every 10,000 to get a blood clot when taking combined contraceptives for one year. By comparison, they would expect to see two cases of blood clots among 10,000 people not using these contraceptives.

What are the symptoms of a blood clot?

Although it's very unlikely that your combined contraceptive will cause a blood clot, it’s still a good idea to familiarise yourself with the symptoms so you can get medical help if you need it.

Blood clots usually develop in the lower legs, so you may initially notice symptoms there, including: 

1. Throbbing or cramping pain in the leg or arm 
2. Swelling, redness, and warmth in the leg or arm 
3. Sudden breathlessness and sharp pain in the chest, as well a cough that may bring up blood

A blood clot that’s travelled to the lungs may cause sudden breathlessness, chest pain, and coughing that brings up blood.
If you experience any of these symptoms you should call 111 immediately for advice.

Contraceptive pill blood clots

When we talk about the pill and blood clots, we’re referring to the combined contraceptive pill. This is the the only type that’s associated with a risk of blood clots.

Combined contraceptives contain synthetic versions of the female hormones oestrogen and progesterone, which in combination are very effective at preventing pregnancy. However, oestrogen has an effect on the blood, making it more “sticky” and therefore slightly more likely to form clots.

Combined hormones are also used in the contraceptive patch and the vaginal ring, which means these types of contraception are also associated with a slightly increased risk of blood clots.

How do I know if I’m at risk of blood clots?

If you’re thought to be more at risk of blood clots because of your age, weight, medical history, or lifestyle, it’s very unlikely that your GP will prescribe you a combined contraceptive.

Am I at risk of blood clots?

You may be more at risk of blood clots if you fall into any of the following categories:

• You’ve recently had an operation 
• You’re overweight 
• You smoke (or recently quit smoking) aged 35 or older 
• You’ve had a blood clot before 
• You have a family history of blood clots 
• You’re pregnant or you’ve recently had a baby 
• You use combined pill, patch or ring or HRT 
• You have an inflammatory condition like rheumatoid arthritis or Crohn’s disease
• You have certain diseases (e.g. breast cancer, liver disease) 
• You’re taking certain medications 
• You have high blood pressure 

None of these things mean that you’ll definitely get a blood clot, it just means that your risk is increased. Where possible, your healthcare professionals will take preventative steps to avoid increasing your risk further – for instance, your GP won’t prescribe the combined pill if you already have an increased risk of blood clots.

The benefits of the combined pill

News stories about the combined pill, patch and ring tend to focus on the negatives, but there are plenty of benefits.

Firstly, the combined pill, patch and ring are really good methods of birth control. When taken correctly, it’s 99% effective at preventing pregnancy.

Other benefits to the combined pill, patch and ring include: 

• A reduced risk of ovarian, womb and colon cancer 
• Lighter and less painful periods 
• Less severe PMS symptoms

Combined contraceptives are also thought to offer some protection against, fibroids, ovarian cysts, and non-cancerous breast disease.

The mini pill and blood clots

The progesterone-only pill contains just one type of hormone. It does not contain oestrogen. This means that there is no increased risk of blood clots. It can be taken by women who can't take the combined contraceptive for medical reasons.

The progestogen-only pill (POP or “mini” pill) is taken once a day. The main difference is that you have to take it at the same time each day. Certain types of the mini pill can be taken within a 12-hour window; other types must be taken within a three-hour window. There are no varieties of the mini pill that involve a seven-day break.

If you like the ease and convenience of the pill, but you can’t take the combined pill or you don’t want to, the POP is an excellent alternative.

How can I prevent blood clots?

If you’re under medical care – e.g. you’re in hospital for an operation – your doctors will take steps to prevent blood clots if they think you’re at risk. They might organise for you to have daily injections to thin your blood.
Outside of a medical environment, there are a few lifestyle changes you can make to reduce your risk:

• Avoid sitting for long periods and have regular mini breaks to get up and stretch your legs or walk around 
• Stay hydrated by drinking plenty of water 
• If you’re overweight, try to lose some weight 
• Quit smoking 
• Exercise more 
• On long journeys where you have to stay sitting, wear compression socks, wriggle your toes and lower legs as much as possible and keep hydrated.

Blood clots, contraception and the COVID-19 vaccine

There have been many reports about how one of the COVID-19 vaccines can cause blood clots. While this is worrying to hear, it’s important to know that the risk is extremely low; only 1 in 100,000 people having their first dose of the vaccine will develop blood clots. 

The FSRH still advises that people taking combined contraceptives such as the combined pill, patch or ring, should have a COVID-19 vaccine. People on combined contraceptives shouldn’t stop taking these when they’re vaccinated. It won’t help and means you could risk getting pregnant.

If you’re worried about blood clot risk in general with combined contraceptives, you can speak to your GP or send us a message in your Patient Record about switching your contraception.

Other types of contraception

The pill may be the most popular type of contraception among women, but there are many other options if it’s not right for you. If you have trouble remembering to take your pill, or if you simply don’t want to have to think about contraception, consider a long-acting reversible method. 

LARCs available in the UK are: 

• The copper coil (IUD) – lasts five to 10 years
• The intrauterine system or hormonal coil (IUS) – lasts three to five years
• The implant – lasts three years
• The injection – lasts eight to 13 weeks

The coil, IUS, and implant all have to be fitted and removed by a healthcare professional. Injections should also usually be given by a healthcare professional.

Stock up on routine contraception with Online Doctor

At Online Doctor we stock a range of contraceptive pills, including the traditional combined pill, the low-dose pill, and the mini pill. Visit our contraception clinic to browse pills and learn more about their benefits.

References

https://www.statista.com/statistics/573210/contraceptive-use-among-women-by-type-and-age-in-england/
https://digital.nhs.uk/data-and-information/publications/statistical/sexual-and-reproductive-health-services/2018-19
https://www.mayoclinic.org/symptoms/blood-clots/basics/definition/sym-20050850
https://www.nhs.uk/conditions/blood-clots/
https://thrombosisuk.org/admin/resources/downloads/thrombosisuk-thrombosis-women.pdf
https://www.theguardian.com/society/2021/apr/09/contraception-blood-clot-risk-public-need-better-access-to-advice
https://www.nhs.uk/conditions/contraception/combined-contraceptive-pill/
https://www.nhs.uk/conditions/contraception/the-pill-progestogen-only/
https://www.fsrh.org/news/fsrh-new-guidance-pill-blood-clots-astrazeneca-april-2021/
https://patient.info/allergies-blood-immune/deep-vein-thrombosis-leaflet
https://www.pontprennaumc.wales.nhs.uk/website/W97065/files/COC%20Pill.pdf
https://www.bmj.com/content/373/bmj.n1005   
https://patient.info/news-and-features/does-the-contraceptive-pill-increase-your-risk-of-blood-clots