How quickly can birth control cause blood clots? Understanding the timeline and risks

October 7, 2025 •

4 min read

While the absolute risk remains low, studies show that using birth control pills and other combined hormone-based contraceptives can increase the risk of blood clots up to three-fold. The risk timeline is critical, with the highest likelihood of developing a clot occurring during the first few months of starting a combined hormonal method, which is key to understanding how quickly can birth control cause blood clots.

Quick Summary

The risk of blood clots is highest during the first 6 to 12 months of starting a combined hormonal contraceptive method. Individual risk factors like smoking, obesity, and age also significantly impact this risk. This increased tendency is primarily linked to the estrogen component, and the risk drops significantly within weeks of stopping the medication. Progestin-only methods do not appear to carry the same level of risk.

Key Points

Highest Risk Period: The risk of blood clots from combined hormonal birth control is highest during the first 6 to 12 months of use.
Estrogen's Role: The primary driver of increased clot risk in contraceptives is the estrogen component, which raises the level of clotting factors in the blood.
Progestin-Only Safety: Methods containing only progestin, such as the mini-pill and hormonal IUDs, do not appear to carry the same increased risk.
Individual Factors: Certain factors like smoking, obesity, age over 35, and family history can significantly increase the risk beyond hormonal contraception alone.
Risk Reversal: After stopping hormonal contraception, the elevated risk of blood clots rapidly returns to near-baseline levels within two to four weeks.
Immediate Medical Attention: Symptoms like leg swelling, chest pain, or shortness of breath require immediate medical evaluation to rule out a blood clot.

How Hormonal Birth Control Influences Blood Clotting

Hormonal birth control, particularly those containing estrogen, can affect the body's natural clotting mechanisms. Estrogen increases the levels of certain blood-clotting proteins in the liver, making blood slightly more prone to clotting. This is a normal physiological process, as the body balances factors that promote clotting with those that prevent it. The hormonal changes induced by contraception can shift this balance, creating a pro-clotting state. While the absolute risk remains very low, affecting a small percentage of users, it is a risk that requires consideration, especially when compounded by other factors.

The Critical Timeline: Highest Risk During Initial Use

For those on combined hormonal contraceptives (CHCs), which include estrogen and progestin, the highest risk of developing a blood clot, or venous thromboembolism (VTE), is concentrated in the early months of use. Medical studies have shown that the risk is most elevated within the first 6 to 12 months after starting the medication. The body is undergoing a significant hormonal adjustment during this period, and it is during this initial phase that the risk of clotting is most pronounced. Over time, this risk decreases but does not disappear completely for the duration of continued use. It's important to note that the risk of blood clots during pregnancy and in the postpartum period is significantly higher than the risk associated with hormonal birth control.

Different Contraceptive Types and Their Clotting Risks

Not all birth control methods carry the same level of risk. The formulation and method of delivery can play a significant role. The risk is primarily associated with combined hormonal methods that contain estrogen. Progestin-only contraceptives generally do not appear to increase the risk of VTE.

Hormonal Birth Control Options and Their Associated Clot Risk


Contraceptive Type	Hormones	Associated Blood Clot Risk	Notes
Combined Oral Contraceptives	Estrogen & Progestin	Increased risk, highest in the first year. Some newer progestins (e.g., drospirenone) potentially carry higher risk than older ones.	Most common type. Risk varies by specific formulation.
Contraceptive Patch	Estrogen & Progestin	Potentially higher risk than low-dose pills due to greater estrogen delivery.	Transdermal delivery.
Vaginal Ring	Estrogen & Progestin	Similar risk profile to combined oral contraceptives.	Localized hormonal release.
Progestin-Only Pill ('Mini-pill')	Progestin Only	Little to no increased risk.	Does not contain estrogen.
Hormonal IUD (e.g., Mirena)	Progestin Only	Little to no increased risk.	Localized hormonal delivery.
Contraceptive Implant (e.g., Nexplanon)	Progestin Only	Little to no increased risk.	Subdermal delivery.
Copper IUD	Non-hormonal	No increased risk.	Non-hormonal method.

Risk Factors That Increase Susceptibility

While hormonal contraceptives can increase clot risk, several other factors can significantly multiply this risk. It is crucial to discuss these factors with a healthcare provider before beginning any new contraceptive method.

Smoking: Smoking, especially for women over 35, dramatically increases the risk of serious cardiovascular events, including blood clots.
Age: The risk of blood clots naturally increases with age, and using CHCs compounds this risk in older women.
Obesity: Being overweight or obese is a known risk factor for VTE.
Family History: A personal or family history of blood clots or genetic clotting disorders (e.g., Factor V Leiden) can significantly increase susceptibility.
Immobility: Long periods of sitting, such as during long travel or after major surgery, increase the risk of deep vein thrombosis (DVT).
Medical Conditions: Certain underlying health issues like high blood pressure, diabetes, and inflammatory bowel disease can also contribute to an elevated risk.

Identifying a Blood Clot: Symptoms to Watch For

Recognizing the signs of a blood clot is critical for timely medical intervention. Symptoms can vary depending on the clot's location. If you experience any of the following, seek immediate medical attention.

Deep Vein Thrombosis (DVT) in a Leg or Arm:

Swelling, often in one leg or arm
Pain, tenderness, or cramping
Warmth to the touch
Redness or discoloration of the skin

Pulmonary Embolism (PE) in the Lungs:

Sudden shortness of breath
Sharp chest pain that worsens with deep breaths or coughing
Rapid or irregular heartbeat
Dizziness or fainting

The Risk After Stopping Contraception

For many women, the increased risk of blood clots is not permanent. Research indicates that the risk largely subsides shortly after discontinuing a combined hormonal contraceptive. In a study published in Blood, researchers found that clotting risk rapidly decreased within two to four weeks after cessation, with biomarkers returning to baseline levels by 12 weeks. This provides important guidance for patients facing planned events like surgery, where a temporary discontinuation of contraception may be advised.

Conclusion

While the absolute risk of blood clots from hormonal contraception is low, understanding the timeline and specific risk factors is essential for safe use. The highest risk period is concentrated within the first year of starting a combined hormonal method, and this risk is significantly amplified by individual factors such as smoking, obesity, and genetic predispositions. Progestin-only and non-hormonal methods offer alternatives with little to no increased risk. Anyone considering hormonal birth control should have a thorough discussion with their doctor to review their personal and family medical history. Recognizing the signs of a blood clot and seeking immediate medical help is paramount for a positive health outcome.

For more detailed information on contraception options and risks, visit the American Society of Hematology.

Frequently Asked Questions

No, only combined hormonal birth control methods containing estrogen are associated with an increased risk of blood clots. Progestin-only methods and non-hormonal options do not carry this risk.

The risk of blood clots is highest during the first 6 to 12 months of starting a combined hormonal contraceptive. After this period, the risk level decreases but remains elevated compared to non-users.

Common symptoms of a deep vein thrombosis (DVT) include swelling, pain, warmth, or redness in a leg or arm. A pulmonary embolism (PE) may cause shortness of breath, chest pain, or rapid heartbeat.

Your risk may be higher if you smoke, are over 35, are obese, have a family history of clotting disorders, or have specific medical conditions. A doctor can assess your personal risk profile.

The elevated risk of blood clots largely diminishes within two to four weeks after stopping combined hormonal birth control. Clotting markers often return to baseline by 12 weeks.

Older, second-generation combined pills with lower estrogen doses and progestins like levonorgestrel are sometimes associated with a lower risk than newer, third-generation pills with different progestins, although the overall risk is still low.

The safest hormonal options are progestin-only methods, such as the mini-pill, hormonal IUDs, or the implant. Non-hormonal options like the copper IUD and barrier methods also carry no risk of hormonal-related blood clots.