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When does the clotting risk rise?
The risk of blood clots with the combined birth control pill is highest soon after starting it. For many people, the increase begins in the first few weeks or months of use.
Research suggests the risk is most noticeable in the first 3 to 6 months after starting the pill. After this period, the risk often settles, but it usually remains a little higher than for someone not taking the pill.
Why the first months matter
The combined pill contains oestrogen, which can make the blood slightly more likely to clot. Your body may be adjusting during the early months of treatment, which is one reason the risk is higher at first.
This does not mean most people will develop a clot. Blood clots are still uncommon, but it is important to know the warning signs, especially when you have recently started the pill.
Who may be at higher risk?
Your personal risk depends on more than the pill itself. Smoking, being overweight, recent surgery, long periods of immobility, and a family history of clots can all raise the chance further.
Risk may also be higher if you are over 35, have migraine with aura, or have certain medical conditions. A GP or pharmacist can help check whether the combined pill is suitable for you.
What symptoms should you watch for?
A blood clot in the leg, called a deep vein thrombosis, can cause swelling, pain, warmth, or redness, usually in one leg. A clot in the lung, called a pulmonary embolism, can cause sudden shortness of breath, chest pain, or coughing up blood.
If you have these symptoms, seek urgent medical help straight away. In the UK, call 999 or go to A&E if symptoms are severe or sudden.
Does the risk stay high forever?
The higher risk is usually greatest early on, then becomes more stable with continued use. However, it does not drop to zero, and the combined pill is still linked with a small increase in clot risk compared with not using hormonal contraception.
If you stop the pill, the extra clotting risk usually falls back over time. The exact timing can vary, but it generally reduces after the pill is no longer in your system.
When to speak to a healthcare professional
If you are thinking about starting the pill and are worried about clots, speak to your GP, practice nurse, pharmacist, or a sexual health clinic. They can explain the risks and talk through other options, including the progestogen-only pill, implant, or coil.
Getting the right contraception for your health and lifestyle matters. If you have any symptoms of a clot, do not wait for a routine appointment.
Frequently Asked Questions
The risk of blood clots after starting the birth control pill is generally low, but it is higher than in people who do not use estrogen-containing birth control. The risk is greatest in the first months after starting and varies based on personal health factors.
The risk of blood clots after starting the birth control pill can increase within the first few weeks to months of use, with the highest risk often occurring in the first year, especially early on.
Combined birth control pills that contain estrogen and progestin carry a higher risk of blood clots after starting the birth control pill than progestin-only methods. Pills with certain progestins may have slightly different risk levels, but estrogen is the main factor.
People with a personal or family history of blood clots, smoking, obesity, age over 35, certain inherited clotting disorders, recent surgery, prolonged immobility, or migraine with aura may have a higher risk of blood clots after starting the birth control pill.
Symptoms can include swelling, pain, warmth, or redness in one leg, sudden shortness of breath, chest pain, coughing up blood, sudden severe headache, vision changes, or weakness on one side of the body. These symptoms need urgent medical attention.
Seek emergency help right away if you have chest pain, trouble breathing, fainting, sudden severe headache, or one-sided leg swelling or pain after starting the birth control pill, as these may signal a dangerous clot.
The risk of blood clots after starting the birth control pill usually decreases after stopping the pill, though the timing depends on the person and whether other clotting risk factors are present.
You can lower the risk of blood clots after starting the birth control pill by avoiding smoking, staying active, maintaining a healthy weight, following your prescriber’s advice, and discussing safer alternatives if you have clotting risk factors.
For many people, the risk of blood clots after starting the birth control pill is lower than the risk during pregnancy and the postpartum period. However, the pill still increases clot risk compared with not using estrogen-containing contraception.
Yes, a family history of blood clots can increase the risk of blood clots after starting the birth control pill, especially if close relatives had clots at a young age or have a known inherited clotting disorder.
Yes, smoking can increase the risk of blood clots after starting the birth control pill, and the risk is especially concerning for people older than 35 who smoke and use estrogen-containing pills.
Yes, age can affect the risk of blood clots after starting the birth control pill. The risk generally rises with age, particularly in people over 35, especially if other risk factors are also present.
Yes, obesity can increase the risk of blood clots after starting the birth control pill. This risk may be higher when obesity is combined with smoking, older age, or other clotting risk factors.
Progestin-only pills generally have a lower risk of blood clots after starting the birth control pill than combined estrogen-progestin pills. They may be a better option for people with elevated clot risk, but a clinician should help choose the right method.
Yes, blood clots can happen after starting the birth control pill even if you have never had one before, although the overall risk remains low for many healthy users.
There is no routine test for everyone to predict the risk of blood clots after starting the birth control pill. A clinician may review your medical history and, in some cases, order blood tests for inherited clotting disorders if your history suggests a higher risk.
Do not stop the birth control pill on your own without medical advice unless you have symptoms of a possible clot and need urgent care. If you are worried about the risk of blood clots after starting the birth control pill, contact a clinician to discuss safer options.
The risk of blood clots after starting the birth control pill is similar to other estrogen-containing methods such as the patch and ring, because estrogen increases clot risk across these options.
Yes, recent surgery can increase the risk of blood clots after starting the birth control pill, especially if you are less mobile during recovery. Tell your clinician about upcoming surgery when discussing contraception.
Tell your doctor about any personal or family history of blood clots, smoking, migraines with aura, obesity, recent surgery, prolonged travel, pregnancy history, and any known clotting disorders so they can assess the risk of blood clots after starting the birth control pill and recommend the safest method.
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