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 Fat Loss vs Wegovy: Which Is Right for You?
Both Mounjaro and Wegovy are prescription-only weight loss injections licensed in the UK, but they work differently and show different results in clinical trials. Mounjaro (tirzepatide) uses a dual GIP and GLP-1 mechanism, while Wegovy (semaglutide) is a GLP-1-only injection. Understanding how they differ can help you and your prescriber decide which weekly weight loss injection might be more suitable for your situation. This guide compares the evidence, mechanisms, and practical considerations for both medications in a UK context.
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.
How Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) activates two hormone pathways simultaneously: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual action may help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. It also slows gastric emptying, though this effect typically reduces over time.
Wegovy (semaglutide) is a GLP-1-only agonist — it activates just the GLP-1 pathway. It works similarly to Mounjaro in reducing appetite and supporting satiety, but without the additional GIP effect. Both are once-weekly injections given as a Mounjaro KwikPen or Wegovy auto-injection pen.
The dual mechanism of Mounjaro may theoretically offer advantages in fat loss, which is reflected in clinical trial comparisons. However, individual responses vary significantly, and the "best" option depends on your personal health profile and prescriber assessment.
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.
SURMOUNT vs STEP Trial Data: What the Evidence Shows
In the SURMOUNT-1 clinical trial, Mounjaro at 15 mg (maximum dose) showed average fat loss of approximately 20.9% of body weight over 72 weeks in adults receiving the full treatment course alongside a reduced-calorie diet and increased physical activity.
In the STEP-1 clinical trial, Wegovy at 2.4 mg (maximum dose) showed average weight loss of approximately 14.9% of body weight over 68 weeks under similar conditions.
These averages highlight that Mounjaro participants lost more weight on average — but results vary widely between individuals. Some people respond better to Wegovy, and some don't respond significantly to either. Your GP or prescriber will assess which is more appropriate based on your health history, other medications, and individual circumstances. Use our GLP-1 weight loss calculator to explore potential outcomes with different medications.
- 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.
Is Mounjaro better than Wegovy for fat loss?
Clinical trials suggest Mounjaro achieved higher average weight loss (20.9% vs 14.9%), but individual results vary significantly. "Better" depends on your personal health profile, how your body responds, and prescriber assessment. Both are licensed in the UK for weight management.
What's the difference between Mounjaro and Wegovy mechanisms?
Mounjaro is a dual GIP and GLP-1 agonist, activating two hormone pathways. Wegovy is GLP-1-only. The dual mechanism may contribute to Mounjaro's higher average weight loss in trials, but both work by reducing appetite and supporting satiety.
How much does each injection cost in the UK privately?
Costs vary by provider and dose. Mounjaro and Wegovy typically range from £129–£320 per month for private prescriptions. NHS access is through specialist tier 3 weight management services, though availability and waiting times vary significantly by region.
Can I switch from Wegovy to Mounjaro?
Yes, switching is possible, but it must be managed by your prescriber. There's no official established conversion between doses — a prescriber will assess your current dose and recommend an appropriate starting dose on Mounjaro. Never switch medications without clinical guidance.
Which injection requires less frequent dosing?
Both Mounjaro and Wegovy are once-weekly injections, so they're equally convenient. Liraglutide (Saxenda) is a daily injection, making Mounjaro and Wegovy more practical for most people managing a weekly schedule.
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.