Birth Control Pills Estrogen Clot Risk

One of the questions most often asked by those who come to be prescribed contraceptive pills is "I heard this drug makes the blood clot—is it okay?" The link between oral contraceptive pills and blood clots (venous thromboembolism) is real, but the risk is not the same for all contraceptive pills. In particular, the fact that even among the same combined oral contraceptive pills, the pattern of clot risk can change depending on the type of estrogen they contain, is not well known. In the clinic, even people who have heard of the difference in progestin generations are rare in considering the differences by estrogen component. Today, let us organize, based on academic society recommendations, how ethinylestradiol, estradiol, and the relatively new estrogen estetrol differ in clot risk.

Combined oral contraceptive pills are medications containing two hormones together, estrogen and progestin. When the side effects of contraceptive pills are discussed, often only the progestin (luteal hormone) generation is mentioned, but the type of estrogen that pairs with it is also an important axis governing clot risk. The estrogens currently in use can be broadly divided into three.

• Ethinylestradiol: a synthetic estrogen that has been the most widely used for decades, contained in most existing contraceptive pills.
• Estradiol (including estradiol valerate): a form close to the estrogen naturally secreted in the human body.
• Estetrol: a natural estrogen made by the fetus during pregnancy, introduced into contraceptive pills relatively recently.

Though grouped under the same name "estrogen," they differ in their effect on the production of coagulation factors in the liver, so the texture of clot risk differs. Understanding this difference makes it understandable why medical staff recommend different preparations for different people.

The key pathway by which estrogen is involved in clot risk is the liver. When estrogen is taken orally, the absorbed component passes through the liver and affects the synthesis of proteins (coagulation factors) involved in coagulation. The stronger this stimulus to the liver, the more the blood may tilt toward coagulating.

Ethinylestradiol's molecular structure is altered in the synthesis process so that it does not break down well in the body, and accordingly it is known to have a relatively strong effect on the liver's production of coagulation factors. By contrast, the natural-type estrogens estradiol and estetrol are reported to have a relatively weak effect on the liver's synthesis of coagulation proteins. In particular, estetrol is a product close to the final stage of estrogen metabolism, and because its effect on the liver is small, it is expected to be advantageous in terms of clot risk.

However, how much such a difference actually reduces clot occurrence in real clinical practice is still at the stage of accumulating long-term data, and you should keep in mind that there can be individual differences.

Recent analyses synthesizing multiple studies organize that contraceptive pills using natural-type estrogen tend to show fewer clot-related reports than ethinylestradiol preparations. A study (2024) analyzing the European Medicines Agency's adverse-event reporting database (EudraVigilance) also reported that combined contraceptive pills based on estradiol or estetrol had a lower rate of venous thrombosis reporting than ethinylestradiol-based preparations, at a level close to progestin-only contraceptive pills.

The table below simplifies and organizes the characteristics by estrogen type. Please view it as a reference for understanding tendencies rather than an absolute grade.

Looking only at this tendency, it is easy to think the natural type is unconditionally better, but variables such as the type of progestin included together, the age and weight of the person taking it, whether they smoke, and family history all affect the risk. Therefore you cannot choose a drug with a single table, and the overall risk factors must be considered together.

If you are worried about contraceptive-pill choice and clot risk, we recommend having your own risk factors checked together at the pregnancy and contraception clinic.

Not only the type but also the dose of estrogen is a factor governing clot risk. In general, the higher the estrogen dose, the more clot risk tends to rise, so contraceptive pills have developed in the direction of lowering estrogen content.

According to the American Society for Reproductive Medicine (ASRM) practice committee's summary (2016, revised 2017), preparations with an ethinylestradiol dose at the 35-microgram level are reported to have clot risk similar to preparations with a lower dose. By contrast, high-dose preparations containing 50 micrograms or more are summarized as having had higher clot risk than low-dose preparations. Fortunately, high-dose oral contraceptive pills of 50 micrograms or more are not generally marketed at present, and the drugs prescribed are mostly low-dose preparations.

In summary, among the low-dose contraceptive pills on the market, the difference in clot risk due to the difference in estrogen dose is not large, and rather the type of estrogen and the progestin paired with it become more meaningful variables. If you are curious about contraception methods overall, you may also refer together to the what types of contraception are available guide.

Many people wonder whether changing the route of administration can avoid clot risk. To say the conclusion first, whether you take the same estrogen orally or apply it as a patch, a meaningful difference in clot risk does not appear well. This is because the component absorbed through the skin also ultimately rides the bloodstream and acts on the liver.

The UK Faculty of Sexual and Reproductive Healthcare (FSRH) combined hormonal contraception guideline (2023) also advises that clot risk must be considered across combined hormonal contraception formulations such as the patch, vaginal ring, and oral preparations. In particular, since some analyses report that the risk at the time of starting patch use is not low, it is difficult to conclude that changing the route makes the risk disappear.

Therefore, rather than a simple swap of "a patch instead of a pill," it is safer to decide on a choice suited to your conditions—smoking, age, weight, family history—by consulting with the medical team.

In clinical experience, the most important thing before starting a contraceptive pill is not choosing the type of drug but first checking your own clot risk factors. This is because even the same drug may not be recommended to someone with overlapping risk factors. The items often checked in the clinic are as follows.

• Whether you smoke and how much, and your age (especially smokers aged 35 and over)
• Comorbidities such as obesity and hypertension
• A personal or first-degree family history of venous thrombosis
• A prolonged immobile state (long-distance flights, post-surgical recovery, etc.)

If you have such factors, it is difficult to consider that changing the estrogen type to a natural type alone lowers the risk sufficiently, and depending on the case, considering an estrogen-free contraceptive method may be safer. If symptoms such as sudden swelling and pain in one leg, shortness of breath, or chest pain appear, you must receive medical care immediately. If you need an overall check of women's health, you can be consulted at women's health care.

The difference in clot risk by estrogen type is certainly meaningful, but we do not decide on a drug by that one thing alone. It is true that natural-type estrogen preparations tend to show fewer clot reports, but to reach the most suitable choice you must synthesize the progestin included together, your own health status, and lifestyle habits. In the clinic, even when people come with the same concern, the drug we ultimately recommend differs from person to person.

The safest method is to honestly share your own risk factors and decide the type, dose, and formulation together with the medical team. Since contraception is a choice that changes over a lifetime, rather than continuing to use a once-decided drug, we recommend checking periodically in line with changes in your physical condition. If you have further questions about contraceptive pills and clot risk, please feel free to inquire by chat consultation.

Written by: Lee Dong-hee Director · Obstetrics and Gynecology Specialist · View medical staff profile

First published January 28, 2024 · Last reviewed May 30, 2026

References: FSRH Combined Hormonal Contraception Guideline (2023), American Society for Reproductive Medicine ASRM Practice Committee (2016, 2017), European Medicines Agency EudraVigilance analysis (2024)

This article is intended to provide general health information and does not replace individual diagnosis or treatment. If you have symptoms, please consult through a medical visit.