The UK's most complete GLP-1 guide
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- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Mounjaro and Blood Clots — How Does It Compare to Wegovy?
Blood clots are a serious health concern, and it's natural to want to understand medication risks before starting treatment. Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK, but they work differently and have different safety profiles. This guide compares what clinical trial data shows about blood clot risk with each medication, explains the mechanisms involved, and helps you understand what your prescriber will assess when deciding which treatment is right for you.
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What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Clinical Trial Data: Blood Clot Risk in Mounjaro vs Wegovy
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist studied in the SURMOUNT clinical trials. In SURMOUNT-1 (the main efficacy trial), thromboembolic events (blood clots) were rare in both treatment and placebo groups, with no significant difference in incidence. The most common side effects were gastrointestinal — nausea, diarrhoea, and constipation — rather than vascular events.
Wegovy (semaglutide) is a GLP-1-only receptor agonist studied in the STEP clinical trials. Similarly, blood clot events were uncommon and comparable between Wegovy and placebo groups. The safety profile was largely driven by gastrointestinal effects rather than thromboembolic risk.
- Both medications showed rare thromboembolic events in clinical trials
- Neither medication demonstrated a significantly elevated blood clot risk versus placebo
- Gastrointestinal side effects — not blood clots — are the most common adverse effects with both drugs
- Prescribers consider individual cardiovascular history when assessing suitability
These trial findings are reassuring, though clinical assessment remains essential for anyone with personal or family history of blood clots or cardiovascular disease.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Individual Risk Assessment — How Your Prescriber Decides
Your prescriber will evaluate your personal risk factors before recommending Mounjaro or Wegovy. Pre-existing cardiovascular conditions — including history of deep vein thrombosis (DVT), pulmonary embolism (PE), or stroke — are assessed carefully. Certain medical conditions and medications increase clotting risk independently of these weight loss injections.
- Personal history of DVT, PE, or thrombotic stroke requires specialist assessment
- Family history of blood clots or cardiovascular disease is reviewed
- Current medications affecting clotting (anticoagulants, antiplatelet drugs) are considered
- Cancer, immobility, recent surgery, or hormone therapy all influence prescriber decision-making
- Both medications require a clinical assessment — neither is suitable for everyone
If you have any concern about blood clot risk, discuss this openly with your GP or prescriber before starting either medication. Use our free BMI calculator to understand your current health metrics, and our GLP-1 weight loss calculator to explore what treatment might mean for you — but prescriber guidance is essential.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Does Mounjaro increase the risk of blood clots?
Clinical trial data (SURMOUNT-1) shows thromboembolic events were rare with Mounjaro and similar to placebo. However, if you have personal or family history of DVT, PE, or stroke, your prescriber must assess your individual risk. Blood clot risk is influenced by many factors beyond medication — immobility, recent surgery, cancer, and certain conditions all play a role.
Is Wegovy safer than Mounjaro for blood clot risk?
No significant difference has been demonstrated between the two medications for blood clot risk. Both are prescription-only and require clinical assessment. STEP trial data for Wegovy showed similarly rare thromboembolic events. Your prescriber will choose based on your full health picture, not on theoretical clot risk differences between the medications.
What should I tell my GP about blood clot risk?
Mention any personal history of deep vein thrombosis (DVT), pulmonary embolism (PE), or thrombotic stroke. Also disclose family history of blood clots, current anticoagulant medications, recent surgery or immobility, cancer, or use of hormone therapy (including oral contraceptives). This helps your prescriber assess whether either GLP-1 medication is suitable for you.
Can I take Mounjaro or Wegovy if I'm on anticoagulants?
Yes, many patients take GLP-1 medications alongside anticoagulants like warfarin or DOACs, but this must be managed by your prescriber. Ensure your GP or prescriber knows all your current medications. Some oral medications have reduced absorption with GLP-1 treatment, so timing and dosing may need adjustment — never stop anticoagulants without medical guidance.
What are the most common side effects of these medications?
Gastrointestinal effects dominate — nausea, diarrhoea, vomiting, constipation, and stomach pain occur in many users. Blood clots are rare with both medications. Most side effects are mild to moderate, improve over time, and resolve after stopping treatment. Start with a low dose and escalate gradually to minimise GI symptoms. Your prescriber will monitor you throughout treatment.
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