Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
There’s been growing discussion online about whether semaglutide — the active ingredient in popular medications like Ozempic, Wegovy and Rybelsus — can cause blood clots. With millions of prescriptions written worldwide for diabetes and weight management, it’s important to separate real clinical evidence from anecdote or misunderstanding. Current large-scale clinical trial data and regulatory product information do not show a direct causal link between semaglutide and blood clot formation (such as deep vein thrombosis or pulmonary embolism). However, people taking semaglutide often have pre-existing risk factors for clots that could independently raise their risk, and vigilance with symptoms matters no matter your treatment.
This article explains how semaglutide works, how blood clots form, what the research says about clot risk and side effects, who may be more vulnerable, and how you can reduce your clot risk while taking semaglutide.
How Semaglutide Works in the Body
Semaglutide is a glucagon-like peptide-1 (GLP-1) receptor agonist — a class of medications that mimics a naturally occurring hormone involved in appetite, digestion and insulin regulation. It slows gastric emptying, reduces hunger signals to the brain and stimulates insulin release when blood glucose is elevated, helping people with type 2 diabetes or obesity improve glycemic control and often reduce body weight.
Unlike medications that act directly on blood vessels or coagulation pathways, the pharmacological action of semaglutide does not inherently promote clot formation. The drug’s established benefits include improvements in major adverse cardiovascular events in high-risk patients in large clinical trials, rather than signals of increased clot risk.
How Blood Clots Are Made and What the Types Are
Blood clots are part of the body’s normal process to prevent bleeding after injury. When the body detects vessel damage, platelets and clotting proteins form a plug to stop blood loss. However, clotting can sometimes happen inappropriately, leading to health problems.
There are two main types of pathological clotting: venous thromboembolism (VTE) — including deep vein thrombosis (DVT) in the legs, and pulmonary embolism (PE) when a clot travels to the lungs — and arterial thrombosis, which can block arteries supplying the heart or brain. Both are medical emergencies requiring urgent care.
Risk factors for inappropriate clot formation include immobility, certain genetic clotting disorders, obesity, smoking and dehydration, among others. These factors influence clot risk independently of medications you take.
Link Between Semaglutide and Blood Clots
So, does semaglutide itself cause blood clots? According to regulatory safety data and the largest clinical trials conducted to date, no causal relationship has been established. Venous thromboembolism, pulmonary embolism or other forms of clotting are not listed as recognised adverse reactions in semaglutide product labels approved by regulators in the US, UK and EU.
Semaglutide’s cardiovascular outcomes trials (such as the SUSTAIN and SELECT programmes) have generally shown neutral or beneficial effects on major cardiovascular outcomes and no significant increase in clotting events compared to placebo.
Some meta-analyses and commentary have suggested an association between semaglutide and increased DVT risk in certain populations, but these findings are controversial and do not by themselves prove causation — especially given confounding factors like underlying metabolic disease and dehydration from gastrointestinal side effects.
Post-marketing surveillance sometimes reports thrombotic events in people on semaglutide, but such reports do not establish that the drug caused the clots, particularly when other risk factors are present.
In short, the current consensus in clinical evidence and regulatory guidance is that semaglutide does not independently trigger blood clot formation, though ongoing monitoring continues as real-world data accumulate.
Possible Side Effects of Semaglutide
While blood clots are not a recognised common side effect in official prescribing information, semaglutide can cause several effects that — in extreme circumstances — might indirectly influence clotting risk if unmanaged.
Semaglutide can cause significant gastrointestinal symptoms that lead to fluid loss, such as vomiting or diarrhoea. Severe dehydration thickens the blood and increases clot risk.
Rapid weight loss seen with any intervention has been associated with transient changes in blood markers, including factors influencing coagulation. While semaglutide-associated weight loss is generally gradual, vigilance around lifestyle and hydration helps mitigate unintended metabolic stress.
Nausea is among the most common side effects of semaglutide, especially during dose escalation. Persistent nausea can reduce appetite and oral intake, which might contribute to dehydration without proper management.
Frequent vomiting can lead to fluid and electrolyte loss, compounding dehydration risk and potentially affecting overall blood viscosity.
Like vomiting, diarrhoea can accelerate fluid loss and increase the risk of dehydration if not addressed with adequate oral intake.
Though less directly linked to dehydration, severe constipation can cause discomfort and reduced mobility, which is a known risk factor for clot formation if prolonged.
While appetite reduction is a therapeutic goal, it can make maintaining hydration and balanced nutrition more challenging if not actively managed.
Fatigue can reduce physical activity levels, and prolonged inactivity is a known risk factor for venous clots.
Dizziness can result from dehydration, low blood pressure or electrolyte imbalance — conditions that can accompany the gastrointestinal side effects of semaglutide.
Who Are at Risk of Clots
The risk of clotting is influenced by many personal and health factors that don’t necessarily relate to semaglutide itself. People with one or more of these characteristics should discuss clot risk with their healthcare provider:
People with a history of blood clots, as recurrence rates are higher if you’ve had clots before.
Individuals with clotting or bleeding disorders (inherited or acquired).
People with limited mobility or a sedentary lifestyle, which slows circulation and increases venous clot risk.
Those who are dehydrated, given thicker blood raises clot risk indirectly.
Individuals experiencing rapid or extreme weight loss, which may transiently affect clotting profiles.
Smokers, who have higher overall clot and cardiovascular risk.
People with obesity-related circulation issues prior to medication use.
Those taking medications that increase clot risk, such as hormone therapies or certain contraceptives.
For anyone with these risk factors, personalised discussion with a clinician before and during semaglutide therapy enhances safety.
Best Ways to Avoid Blood Clots While on Semaglutide
Even if semaglutide doesn’t directly cause clots, you can support vascular health while taking it by:
Staying well hydrated throughout the day, especially if you experience gastrointestinal side effects. Maintaining hydration keeps blood viscosity normal and supports circulation.
Avoiding rapid or extreme weight loss, aiming for steady, clinician-guided progress rather than quick changes.
Moving regularly and avoiding long periods of sitting, since physical activity stimulates circulation and reduces venous stasis.
Following the prescribed dosage instructions and reporting side effects like severe diarrhoea or vomiting promptly.
Monitoring for unusual swelling or pain, particularly in the legs, chest or shortness of breath — these may signal clot formation regardless of cause.
Maintaining regular follow-ups with a healthcare provider so risk factors can be assessed and managed over time.
Discussing personal clot risk before starting treatment, especially if you have a history of clots or a clotting disorder.
Summary
Current clinical evidence does not establish that semaglutide directly causes blood clots, and regulatory safety data do not include thrombotic events as recognised side effects of the medication. Because semaglutide users often have underlying conditions like obesity or diabetes that independently raise clot risk, it’s important to manage personal risk factors and monitor symptoms carefully. Maintaining hydration, staying active and working with your healthcare provider helps you enjoy semaglutide’s benefits while reducing avoidable vascular risks.
If you’d like, I can add a short FAQ section (e.g. “Can dehydration increase clot risk?” or “What symptoms of DVT should I look for?”) to make this article even more practical for readers.
Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.