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
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Mounjaro vs Wegovy: Weight Loss Tracking Comparison
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK, but they work through different mechanisms and deliver different clinical trial results. If you're considering either medication and want to track your potential weight loss, understanding the key differences can help you have an informed conversation with your GP or prescriber. This guide compares the two medications side-by-side, covering how they work, expected weight loss, and how to monitor your progress.
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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 Results and Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways to regulate appetite and support weight management. In the SURMOUNT-1 clinical trial, participants taking the maximum 15 mg dose lost an average of approximately 20.9% of their body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, working through a single hormone pathway. In the STEP-1 clinical trial, participants taking the maximum 2.4 mg dose achieved an average weight loss of approximately 14.9% of body weight over 68 weeks with the same lifestyle support.
- Mounjaro: dual mechanism may support slightly greater average weight loss
- Wegovy: proven single-pathway approach with extensive clinical data
- Both: individual results vary significantly — these are clinical trial averages, not assured outcomes
- Both: prescribed alongside a weekly weight loss injection and complementary lifestyle changes
Use our GLP-1 weight loss calculator to estimate potential weight loss projections at different dose levels for either medication.
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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.
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Doses, Injection Schedules, and Tracking Your Progress
Both medications are administered as once-weekly injections using pre-filled pens. Mounjaro escalates from 2.5 mg to a maximum of 15 mg over approximately 20 weeks, whilst Wegovy escalates from 0.25 mg to 2.4 mg over approximately 16 weeks. Your prescriber will adjust doses gradually, monitoring your response and tolerability at each stage. When tracking your weight loss, expect initial changes within 2–4 weeks, with more significant progress by week 8–12. Both medications work best when combined with a reduced-calorie diet and regular physical activity. Track your weight weekly using our free progress tracker to monitor trends alongside your injection schedule. Most users maintain a weight loss log to correlate dose changes with progress, helping your prescriber optimise your treatment plan over time.
- 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.
Which medication causes more weight loss — Mounjaro or Wegovy?
Clinical trial data suggests Mounjaro (tirzepatide) achieved slightly greater average weight loss (20.9% at maximum dose) compared to Wegovy (14.9% at maximum dose). However, individual results vary significantly, and the best choice depends on your personal health profile, tolerability, and prescriber recommendation.
Can I switch from Wegovy to Mounjaro or vice versa?
Any switch between medications must be managed by your prescriber — do not attempt this independently. Approximate dose equivalences exist, but there is no official NHS conversion chart. Your GP or specialist will assess whether switching is appropriate and manage the transition carefully.
How do I track weight loss on Mounjaro or Wegovy?
Weigh yourself weekly at the same time of day, using the same scales. Record your weight in a log or use a weight tracking app to identify trends over 4-week periods (one injection cycle). Our free progress tracker is designed specifically to monitor weight loss medication journeys. Share records with your prescriber at review appointments.
How often should I expect to see weight loss results?
Initial changes may appear within 2–4 weeks, though some users see results sooner. Most significant progress occurs by weeks 8–12. Weight loss is not linear — expect plateaus, especially between dose increases. Consistency with both the injection schedule and lifestyle changes (diet and exercise) is key.
Are Mounjaro and Wegovy available on the NHS or only privately?
Both are NHS-approved through tier 3 specialist weight management services, but availability and waiting times vary significantly by region. Private prescription is also available through GPhC-registered online prescribers following a clinical assessment. Your GP can advise on NHS access in your area.
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.