DVT and Blood Clots with Obesity: Estrogen, Surgery and What GLP-1 Data Show

Deep vein thrombosis (DVT) is a blood clot in a deep vein, usually in the leg. If part of it breaks off and lodges in the lungs, it becomes a pulmonary embolism (PE). Together they are called venous thromboembolism (VTE). PE affects roughly 370,000 people a year in the United States and causes an estimated 60,000 to 100,000 deaths ^[2]. Obesity roughly doubles the risk of VTE ^[3], genetic evidence suggests that link is causal ^[4], and obesity multiplies the extra risk that comes with estrogen-containing pills ^[5][6]. This review covers the symptoms, those interactions, the surgical window, what weight loss changes, and what the evidence says about GLP-1 drugs such as semaglutide and tirzepatide.

The honest summary

• Obesity is an established clot risk factor. It carried 2.33 times the odds of VTE in a meta-analysis ^[3], and severe obesity 5 times the risk of a DVT that spreads to the lungs in a Danish cohort ^[4].
• Obesity plus oral estrogen is the dangerous combination. Women with obesity on oral contraceptives had 24 times the odds of a clot of normal-weight non-users ^[5]. With menopausal hormone therapy, the extra risk was seen with oral estrogen, not with patches or gels ^[6][7].
• Surgery briefly raises risk, and weight-loss surgery lowers it long-term. VTE risk was 5 times higher in the 30 days after bariatric surgery, and about 40% lower at five years ^[9].
• GLP-1 trial data conflict. One meta-analysis of trials found more DVT on GLP-1 drugs ^[11]; another, limited to placebo-controlled trials, found fewer PEs and no difference in DVT ^[12].
• Health-record studies mostly show fewer clots on GLP-1 drugs ^[13][14], but they cannot rule out that users were healthier to begin with.

DVT and pulmonary embolism symptoms

The most common signs of a leg DVT are swelling (in about 71% of cases) and a cramping or pulling discomfort in the calf or thigh (about 53%) ^[1]. Because many other conditions cause similar symptoms, diagnosis combines a clinical probability score, a D-dimer blood test and an ultrasound of the leg veins ^[1]. A red, hot, swollen leg can also be cellulitis, a skin infection that shares several risk factors with DVT; see cellulitis, obesity and lymphedema.

PE should be suspected with sudden chest pain, shortness of breath or fainting ^[2]. Recent surgery or trauma, a past clot, one-sided leg swelling and estrogen use are among the features clinicians check when judging how likely a PE is ^[2].

A clot is not a one-time problem for many people. Recurrence rates range from 20% to 36% over the 10 years after a first event, and post-thrombotic syndrome, with lasting leg pain, swelling and skin changes, develops in 25% to 50% of patients within months of a DVT ^[1].

How much does obesity raise the risk?

A meta-analysis of 21 studies with 63,552 patients put the odds of VTE at 2.33 times higher with obesity, a stronger association than for high blood pressure (1.51) or diabetes (1.42) ^[3]. In the Dutch MEGA study of 3,834 people with a first clot, overweight raised the odds 1.7-fold and obesity 2.4-fold ^[5].

The risk climbs with weight. In the Copenhagen study of 87,574 adults, compared with normal weight, the risk of DVT was 1.3 times higher with overweight, 1.8 times with moderate obesity and 3.4 times with severe obesity; for DVT complicated by PE, severe obesity carried 5.1 times the risk ^[4]. A gene variant that raises BMI (FTO) also raised the risk of DVT with PE, which supports a causal link rather than a coincidence of lifestyle.

Estrogen, the pill and obesity

Obesity and estrogen-containing medicines add to each other. In MEGA, women with obesity who used oral contraceptives had about 24 times the odds of a clot compared with normal-weight women not on the pill ^[5]. If you are on a GLP-1 drug and use hormonal contraception, there are also drug-interaction questions; see GLP-1 drugs and birth control.

For menopausal hormone therapy, the route of estrogen matters. In the French ESTHER study, obesity alone raised the odds of a clot about 4-fold. Women with obesity on oral estrogen had about 20 times the odds of normal-weight non-users, while women with obesity using transdermal estrogen had about the same risk as women with obesity using no hormones ^[6]. A UK study of more than 80,000 women with VTE found the same pattern: oral hormone therapy raised the odds by 58%, while patches and gels were not linked to higher risk (odds ratio 0.93) ^[7]. Among oral products, conjugated equine estrogen with medroxyprogesterone carried the highest risk and estradiol with dydrogesterone the lowest.

The FDA label for conjugated estrogens (Premarin) also addresses surgery directly:

“If feasible, estrogens should be discontinued at least 4 to 6 weeks before surgery of the type associated with an increased risk of thromboembolism, or during periods of prolonged immobilization.” ^[8]

— Premarin prescribing information, Warnings and Precautions 5.1 (DailyMed)

How estrogen therapy and GLP-1 drugs fit together for weight, and what the evidence says about combining them, is covered in GLP-1 drugs with HRT in menopause.

Surgery, the perioperative window and weight-loss surgery

Recent surgery is one of the features that raises the likelihood of a clot ^[2]. A US study of 30,171 bariatric surgery patients and 218,961 matched controls shows both sides of it ^[9]. In the 30 days after surgery, VTE risk was about five times higher than in controls (hazard ratio 5.01). By one year, risk was 48% lower, and at five years it remained 41% lower, with PE 55% lower. A UK study following 4,056 bariatric patients for a median of 10.7 years found a 40% lower long-term VTE risk, driven by fewer DVTs (hazard ratio 0.52); PE was not significantly reduced ^[10].

For people taking a GLP-1 drug before an operation, a 2026 meta-analysis of 13 cohort studies in hip and knee replacement found no association between GLP-1 use and VTE or PE after surgery ^[17]. Perioperative guidance on GLP-1 drugs centers on slowed stomach emptying under anesthesia rather than on clotting; it is summarized in GLP-1 drugs before surgery.

Do GLP-1 drugs raise or lower clot risk?

The randomized-trial evidence comes from safety events recorded in trials designed for other purposes, and two 2025 meta-analyses read it differently.

• Possibly more DVT. Pooling 39 trials with 70,499 participants, including trials against other diabetes drugs, overall VTE was not significantly increased (odds ratio 1.19), but DVT was (odds ratio 1.64), about 25 extra cases per 10,000 person-years ^[11]. The signal was strongest in trials lasting more than 18 months and in cardiovascular outcome trials. PE was not increased.
• Possibly fewer PEs. Pooling 27 placebo-controlled trials with 84,003 patients, overall VTE was not significantly different (risk ratio 0.70), PE was lower (risk ratio 0.60) and DVT was not different (risk ratio 1.21) ^[12]. The median VTE rate was 1.1 per 1,000 patient-years on GLP-1 drugs and 2.5 on placebo.

Clots were rare in these trials, about 1 to 2.5 per 1,000 patient-years ^[12], so a handful of cases can shift the result. What they agree on is that any effect is small in absolute terms and that no large shift in clot risk has shown up in the trials.

Health-record studies

Observational studies have mostly pointed toward fewer clots. In a target-trial emulation of 540,258 people with type 2 diabetes, new GLP-1 users had a lower one-year VTE rate than new users of DPP-4 inhibitors (6.1 vs 7.6 per 1,000 patient-years; hazard ratio 0.78) ^[13]. A 2026 meta-analysis of six active-comparator studies in diabetes found GLP-1 drugs and SGLT2 inhibitors were each associated with about 20% to 30% lower VTE risk than DPP-4 inhibitors, with no clear difference between the two ^[14]. In people with obesity and chronic venous insufficiency, GLP-1 users had fewer DVTs (hazard ratio 0.54) and PEs (hazard ratio 0.43) ^[18].

For tirzepatide, one study compared people with type 2 diabetes and overweight or obesity starting the drug with matched people on lifestyle advice alone and reported about 70% to 80% fewer PEs and DVTs at one year ^[15]. A second study, comparing tirzepatide with GLP-1 drugs in obesity, found a modestly lower VTE risk (hazard ratio 0.90), driven by PE, with no difference in DVT ^[16].

Effects of 70% to 80% in a year are larger than anything seen in the randomized trials ^[11][12], which points to healthy-user bias: people who get prescribed and stay on a new weight-loss drug may differ from those who do not in ways that matching cannot capture. The study in venous disease also found a 9-percentage-point survival advantage at three years, another sign of the same problem ^[18]. These studies are reassuring on one point, that GLP-1 drugs do not appear to cause a large rise in clots, but they cannot show that the drugs prevent them.

If you have had a clot

Direct oral anticoagulants such as apixaban and rivaroxaban work as well as warfarin for treating a DVT and cause less major bleeding (1.1% vs 1.8%) ^[1]. Severe obesity and bariatric surgery raise specific dosing and absorption questions, and the International Society on Thrombosis and Haemostasis has issued guidance on using these drugs in people with obesity and after bariatric surgery ^[19]. If you take a blood thinner and are starting a GLP-1 drug, see GLP-1 drugs with warfarin, Eliquis and Xarelto.

Practical steps

• Know the warning signs. One-sided leg swelling or calf pain needs same-day care; sudden breathlessness or chest pain needs emergency care ^[1][2].
• If you have obesity and use estrogen, ask about the route. Transdermal menopausal estrogen was not linked to added clot risk, unlike oral estrogen ^[6][7].
• Before planned surgery, tell your team about hormone therapy, the pill and any GLP-1 drug ^[8].
• Treat weight loss as long-term risk reduction. Lower weight after bariatric surgery was followed by fewer clots over years ^[9][10].
• Do not stop or start a GLP-1 drug because of clot risk alone. The trial evidence shows no large effect either way ^[11][12].