Blood clots and birth control – what are the risks?

Doctors use the term venous thromboembolism (shortened to VTE) to refer to blood clots that form in deep veins (deep vein thrombosis) often in the leg. Blood clots can also dislodge and travel to blood vessels elsewhere in the body – such as the lungs (which is known as a pulmonary embolism)².

If a blood clot blocks an artery it can prevent blood reaching important organs like the brain, leading to stroke or heart leading to a heart attack. In worst case scenarios this can result in long term, irreversible damage, or death.

Which all sounds pretty scary.

How does birth control cause blood clots?

Most forms of contraception use the hormones oestrogen and progestin, also known as progestogen. Researchers have known since the 1970s that there is a relationship between contraception containing synthetic oestrogen and blood clots.

While the exact mechanism isn’t known, research suggests that oestrogen reduces the body’s ability to regulate clotting. This makes the blood less able to stop forming clots even when it’s not the right time or place.

More specifically, oestrogen appears to dull the body’s sensitivity to an enzyme called activated protein C (APC). APC reduces clotting, which means it acts to slow or stop the blood clotting. With the body less sensitive to APC, the blood is less able to stop clotting.

Research studies have shown higher levels of APC resistance in people taking the combined pill compared to those who are not taking the pill^3,4,5.

Before we continue, let’s take a moment to talk risk.

What is the increased risk of blood clots?

Whenever we read about increased risk, it’s important to know what the baseline risk is. In this case, baseline risk is the risk of developing a blood clot if you are premenopausal, not pregnant, and not taking any form of birth control.

If we tracked 10,000 such women for a whole year, we would expect between two and six of them to develop blood clots⁶. Put another way, that’s less than 0.1% per year. This baseline risk is so low that increasing it several times over will still result in a very small overall risk for most people.

However, even a small risk can be a cause of concern if you have other risk factors for blood clots, such as a family history. That’s why it’s so important to let your healthcare professional know about your medical and family history before making decisions about your birth control.

Whenever we think about risk of contraception, we have to balance it against the risk of getting pregnant. Pregnancy actually causes a higher risk of blood clots than the pill.

However, everyone is different, and some of us may be happy with the very small increased risk of blood clots for the benefits of contraception, others aren’t. And for others, it might just be a little bit too risky to take certain contraceptives because of their medical history.

Armed with knowledge of the baseline risk, let’s look at different types of contraception.

What is the increased risk of blood clots for different birth control methods?

This table summarises the risk of blood clots for every method of contraception.

Statistics have been taken from the most up to date research study looking at over 1.3 million users.

* These numbers are estimates. They show roughly how many people out of 10,000 might get a blood clot in one year. We worked them out using the risk for people not using hormonal contraception (about 2 in 10,000) and how much each method raises that risk.

** There wasn’t enough information about the patch to adjust for confounding factors like weight and smoking, so its numbers come from the main part of the study.

The combined pill

• The combined pill is made up of oestrogen and progestogen.
• The risk of developing blood clots when taking the combined pill is between 2 and 5 times higher than the risk of blood clots in women who do not take the pill^7,8.
• There are several types of progestogen used in different pill brands.
• We know that progestogens on their own do not appear to increase the risk of blood clots.
• But research has shown that in the combined hormonal contraceptives, different types of progestogen used alongside synthetic oestrogen have different effects on blood clot risk.

Different types of combined pill and blood clot risk

• A study from 2015⁹ investigated this risk a little further, and found differences depending on the type of progestogen used in the birth control pill.
• This large Dutch study that looked at health data from thousands of women aged 15-49 across the Netherlands who had had a blood clot for the first time. They looked at the types of contraceptive they used, if any.
• The research, which has been replicated again in 2025, showed that different types of progestogen used in the combined oral contraceptive pill seem to result in different risk levels for blood clots.
• It is not yet known why.
• You can see in the table below which types of progestogens are associated with an increased risk of blood clots when used in the combined oral contraceptive pill, and which brands contain these different types. 
• Taking a combined pill containing a type of progestogen called levonorgestrel (like Rigevidon or Microgynon) resulted in the lowest increase in blood clot risk, while pills containing cyproterone acetate (Dianette) present the biggest increase in risk.
• The majority of women in the UK already take a combined pill containing the lower risk combination with levonorgestrel¹⁰.
• Pills with other types of progestogen like drospirenone may be offered for other health needs, such as severe acne or PMDD, and for managing side effects women experience on levonorgestrel containing pills.

The patch and the vaginal ring

• Much less research has been conducted into blood clot risk with the patch and vaginal ring.
• The patch contains oestrogen. It does appear to increase blood clots risk, and a large Danish study¹⁴ found that this risk was just over twice the risk of the oral combined pill. 
• The vaginal ring also contains oestrogen, and research suggests it, too, increases blood clot risk¹⁵. In the same Danish study, researchers found the risk was just under two times the risk of the oral combined pill.
• The NHS currently advises against use of the patch or the ring where a woman has a history of blood clots^16,17.
• More research is needed to understand more fully the risk of blood clots associated with both of these forms of contraceptive.

Progestogen-only pill and the implant (Nexplanon)

• Current evidence suggests that progestogen-only pills (like Cerazette or Slynd)  does not increase the risk of blood clots in healthy women.
• The implant also does not increase the risk of blood clots in healthy women^11,12,13. 
• This is why progestogen-only forms of hormonal contraception are often offered as an alternative to the combined pill for women with increased risk of blood clots.

The injection

• The injection only contains progestogen, but updated guidelines from 2025 suggest that it has a higher risk of blood clots than other progestogen-only methods²².
• For this reason, users who may have used the injection before, might be offered different methods if they have other risk factors for blood clots.

The hormonal and copper coils

• There is relatively little published research into the hormonal IUD or copper IUD and blood clot risk, but it is currently understood that neither increase the risk in healthy women^18,19.

Should you be worried about blood clots on the pill

• For most women, the increase in the risk of blood clots from hormonal contraceptives doesn’t present a concern.
• Because blood clots are a much higher risk during pregnancy – four to five times the baseline risk^20,21 and even higher in the first 6 weeks after giving birth, the consensus in the medical profession is that taking the combined pill is safer than pregnancy.
• However, if you have an increased risk of blood clots, your healthcare professional will advise whether the combined pill is safe for you or not. family history of blood clots or a condition that predisposes you to blood clots (such as sickle cell anaemia, or thrombophilia), it’s really important that your healthcare professional knows this before you decide on the best form of contraception. 

What increases the risk of blood clots on the pill?

Risk factors for bloods clots on the pill include:

• Smoking
• Your age, especially over 35
• BMI over 35
• Family history of a blood clot
• Genetic disorders that predispose you to blood clots
• Immobility
• Certain inflammatory or autoimmune conditions such as Lupus

What are the signs of a blood clot?

• Throbbing or cramping pain in the leg or arm
• Swelling, redness and warmth in a leg or arm
• Sudden breathlessness, sharp chest pain (may be worse when you breathe in) and a cough or coughing up blood

If you develop any of these symptoms, seek urgent medical attention.

Remember, the risk of getting a blood clot is low and needs to be balanced against the risk of pregnancy. Everyone is indiviual and has a different medical history or threshold to take this small risk. Your contraceptive choice is individual and speak to a healthcare professional for support.