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 Face vs Wegovy — What's the Difference?
"Mounjaro face" and "Wegovy face" are terms some people use to describe facial changes that may occur during gradual weight management with GLP-1 receptor agonist medications. Both Mounjaro (tirzepatide) and Wegovy (semaglutide) can contribute to facial volume loss as the body loses weight. This guide explains the differences between these two prescription weight loss injections, the clinical evidence, and how to discuss facial changes with your GP or prescriber.
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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.
How Mounjaro and Wegovy Differ in Mechanism and Results
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two hormone pathways simultaneously. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. This dual mechanism may contribute to faster and more substantial weight loss with Mounjaro compared to Wegovy in clinical trials.
In the SURMOUNT-1 trial, participants on Mounjaro 15 mg lost an average of 20.9% of their body weight over 72 weeks. In the STEP-1 trial, Wegovy participants lost an average of 14.9% of body weight over 68 weeks. Faster weight loss — whether from Mounjaro's dual mechanism or individual response — may increase the likelihood of noticeable facial volume changes. However, individual results vary significantly, and some people experience minimal facial changes regardless of weight loss achieved.
Both medications are prescription-only in the UK and require a clinical assessment before being prescribed. Neither is assured to produce specific cosmetic outcomes, and facial changes depend on genetics, age, skin elasticity, and the rate of weight loss.
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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.
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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Which Medication Is Right for You? Individual Suitability
Whether Mounjaro or Wegovy is more suitable for you depends on several factors that your prescriber will assess: your BMI, any weight-related health conditions, your medical history, medications you're taking, and your personal preferences regarding injection frequency (both are once-weekly) and dosing schedules.
If you're concerned about facial changes during weight loss, discuss this openly with your GP or prescriber before starting either medication. They can explain what to expect, discuss strategies to support skin health (hydration, nutrition, skincare), and monitor your progress. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses — this can help you understand the likely extent of change and plan accordingly. Neither medication is "better" cosmetically; individual response varies widely.
- 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 cause more facial changes than Wegovy?
Mounjaro may cause more noticeable facial changes because it typically produces faster and greater weight loss (average 20.9% vs 14.9% in clinical trials). Faster weight loss can mean more rapid facial volume loss. However, individual variation is significant — some people experience minimal facial changes regardless of medication or weight loss amount. Genetics and skin elasticity play major roles.
What causes "Mounjaro face" or "Wegovy face"?
These terms describe facial volume loss that occurs naturally during significant weight loss. The face contains fat deposits that diminish as the body loses weight. This is a normal physiological process, not a side effect specific to either medication. It affects the cheeks, temples, under-eye area, and jawline. The rate of facial changes depends on genetics, age, skin elasticity, and how quickly weight is lost.
Can I prevent facial volume loss while taking Mounjaro or Wegovy?
You cannot entirely prevent facial volume loss during significant weight loss, but you can support skin health by staying well-hydrated, eating nutritious food rich in vitamins and protein, using a good skincare routine, and protecting your skin from sun damage. Some people use dermal fillers to restore volume after weight loss is complete — discuss this with a dermatologist if concerned. Slower, more gradual weight loss may result in less dramatic facial changes.
How do I decide between Mounjaro and Wegovy if I'm worried about facial changes?
If facial aesthetics are a concern, discuss this with your prescriber. Both medications are prescription-only and require clinical assessment. Your prescriber can explain realistic expectations based on your individual situation, your starting weight, and your health goals. Neither medication assures specific cosmetic outcomes. Focus on the health benefits (improved blood sugar control, reduced cardiovascular risk) alongside appearance concerns.
Are Mounjaro and Wegovy the only weight loss injections available in the UK?
No. Other UK-licensed options include Saxenda (liraglutide), a daily GLP-1 injection. All three — Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide) — can contribute to facial changes during weight loss. Your prescriber will recommend the most suitable option based on your health profile, preferences, and clinical evidence. Use our free BMI calculator to understand your current weight category and discuss eligibility with your GP.
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