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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Loose Skin: Mounjaro vs Wegovy — What's the Difference?
Loose skin during significant weight loss is a common concern for people using weight loss medications like Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are GLP-1-based injections licensed in the UK, but they work slightly differently — which may affect how your skin responds during weight loss. Individual results vary widely, and loose skin depends on many factors including age, genetics, how much weight you lose, and how quickly you lose it. This guide compares the two medications fairly and explains what you can realistically expect. Always discuss your personal concerns with your GP or prescriber before starting treatment.
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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.
How Mounjaro and Wegovy Differ in Mechanism and Weight Loss Speed
The key difference between Mounjaro and Wegovy lies in their mechanisms. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. In SURMOUNT-1 clinical trials, participants on 15 mg Mounjaro lost an average of 20.9% of their body weight over 72 weeks. Wegovy (semaglutide) is a GLP-1-only agonist, and STEP-1 trial data showed an average weight loss of 14.9% over 68 weeks at the maximum 2.4 mg dose.
- Mounjaro's dual mechanism may produce slightly faster weight loss in some individuals
- Wegovy's single mechanism is also highly effective but typically results in more gradual loss
- Faster weight loss may increase the risk of noticeable loose skin, though this varies greatly between people
- Both require a UK prescription following clinical assessment and are available through NHS specialist services or private prescribing
Neither medication assures loose skin or prevents it — genetics, age, and skin elasticity play major roles. Use our GLP-1 weight loss calculator above to estimate potential weight loss at different doses with either medication.
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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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Loose Skin, Dose Titration, and Individual Factors
Loose skin develops when weight loss occurs faster than skin can naturally retract. This depends on: age (younger skin is typically more elastic), genetics, starting weight, and how much weight you lose overall. Both Mounjaro (via KwikPen injection) and Wegovy use gradual dose titration — starting at low doses and increasing every 4 weeks — which may help minimise sudden weight loss. However, the clinical difference in loose skin risk between the two medications is not established in trials.
What matters most is your individual circumstances. A prescriber will assess your eligibility based on BMI and health conditions under NHS NICE guidance, and then choose the medication most suitable for you. Check your current BMI using our free BMI calculator above to understand where you sit on the NHS scale. Loose skin concerns are valid — discuss them openly with your GP or weight management specialist when considering either medication.
- 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 loose skin than Wegovy?
No established clinical difference exists. Loose skin depends more on age, genetics, starting weight, and total weight lost than on which GLP-1 medication you use. Mounjaro may result in slightly faster weight loss on average, which could theoretically increase loose skin risk — but individual variation is enormous, and many people experience minimal loose skin with either medication.
Can I prevent loose skin while taking Mounjaro or Wegovy?
Gradual weight loss (0.5–1 kg per week, as recommended by NHS) gives skin more time to adapt. Both medications use dose titration starting low and increasing weekly, which supports gradual loss. Staying hydrated, eating adequate protein, and doing resistance exercise may help skin health during weight loss. Discuss specific strategies with your GP.
Is there a difference between Mounjaro KwikPen injection and Wegovy for loose skin outcomes?
No. Both are delivered via pre-filled injection pens, and the delivery method does not affect loose skin risk. The difference is in the medication itself — tirzepatide versus semaglutide — but clinical evidence does not show one causes significantly more or less loose skin than the other.
How is eligibility for Mounjaro or Wegovy determined in the UK?
Both require a UK prescription following clinical assessment. You typically need a BMI of 30 or above, or 27 or above with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea). NHS NICE guidance applies. Access is through NHS specialist tier 3 weight management services or private online prescribing with a registered UK doctor.
What should I discuss with my GP before choosing Mounjaro or Wegovy?
Mention your loose skin concerns directly. Discuss your age, starting weight, target weight, and how quickly you want to lose weight. Your prescriber will consider your overall health, any medications you take, and which medication they believe is most suitable for you. Both require commitment to dietary changes and physical activity alongside the injection.
Ready to take control of your weight loss journey?
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