The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
Mounjaro, Blood Clots and Wegovy — What the Evidence Shows
Blood clots are a rare but serious concern for any prescription medication. Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are licensed weight management injections in the UK, and both carry similar cardiovascular safety profiles based on clinical trial data. This guide compares how blood clot risk is presented in the evidence for each medication, and explains what you need to know before discussing these treatments with your GP. Individual suitability is determined following a clinical assessment.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
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 Evidence and Safety Data Comparison
The SURMOUNT trials for Mounjaro (tirzepatide) and the STEP trials for Wegovy (semaglutide) both monitored cardiovascular events, including blood clots (venous thromboembolism), as part of their safety oversight. In the SURMOUNT-1 trial, the incidence of blood clot events was low and not significantly higher in Mounjaro groups compared to placebo. Similarly, the STEP trials found rare cases of blood clots, with rates comparable to placebo groups.
- Both medications activate natural hormone pathways (Mounjaro via dual GIP+GLP-1, Wegovy via GLP-1 only) that do not directly increase clotting risk
- gradual weight management itself can theoretically increase blood clot risk — a factor present with both medications
- The MHRA (UK medicines regulator) monitors both medications continuously through post-market surveillance
- Neither medication lists blood clots as a "very common" or "common" side effect in current UK guidance
Both drugs carry a Black Triangle (▼) status in the UK, indicating ongoing monitoring for rare adverse events, including thromboembolic events.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Individual Risk Assessment — What Your Prescriber Will Consider
Your prescriber will assess your personal blood clot risk factors before prescribing either Mounjaro or Wegovy. Risk factors include: previous blood clots, family history of thromboembolism, immobility, recent surgery, oral contraceptive use, smoking, and certain medical conditions. gradual weight management (expected with both medications) may increase clotting risk in vulnerable individuals, which is why clinical assessment is essential.
If you have a personal or family history of blood clots, inform your GP or prescriber immediately. You may not be suitable for these medications, or additional monitoring may be needed. Use our free GLP-1 weight loss calculator to explore projected outcomes, then discuss safety considerations with your healthcare provider in detail.
- 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 carry a higher blood clot risk than Wegovy?
No. Clinical trial data from SURMOUNT (Mounjaro) and STEP (Wegovy) show similarly low rates of blood clots in both groups. Both are licensed for UK weight management with comparable safety profiles. Individual risk depends on personal factors, not the medication choice alone.
What is a blood clot and why might it happen with weight loss injections?
A blood clot (thromboembolism) is when blood thickens and blocks a vein or artery. gradual weight management can theoretically increase clotting risk in some individuals. Both Mounjaro and Wegovy enable gradual weight management, which is why prescribers assess your clotting risk factors before prescribing either medication.
Should I avoid Mounjaro or Wegovy if I have a family history of blood clots?
Not necessarily — but you must inform your GP or prescriber. A family history of blood clots means you may need additional monitoring, or these medications might not be suitable for you. Clinical assessment will determine if either is safe for your individual circumstances.
What symptoms of a blood clot should I watch for?
Seek urgent medical attention if you experience: sudden leg swelling or pain, chest pain or shortness of breath, calf tenderness, or redness in one leg. These could indicate a blood clot. Contact your GP or NHS 111 immediately if you notice these symptoms while taking any weight loss injection.
How does gradual weight management increase blood clot risk?
gradual weight management can cause dehydration and changes in blood composition, which may increase clotting risk in susceptible individuals. Both Mounjaro and Wegovy enable significant weight loss (typically 15–21% body weight), making baseline clotting risk assessment crucial before starting either medication.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.