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 After Mounjaro and Wegovy — What You Should Know
Loose skin can occur after significant weight loss with GLP-1 medications like Mounjaro or Wegovy, though the extent varies considerably between individuals. Both tirzepatide (Mounjaro) and semaglutide (Wegovy) work by reducing appetite and supporting weight loss, which may result in skin changes over time. Understanding how both medications compare, what causes loose skin, and how to manage it can help you make an informed decision alongside your GP or prescriber. This guide compares the two medications in the context of this common concern.
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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.
Mounjaro vs Wegovy — Clinical Trial Outcomes and Skin Changes
In clinical trials, Mounjaro (tirzepatide) demonstrated average weight loss of approximately 15–21% of body weight over 72 weeks, whilst Wegovy (semaglutide) showed average weight loss of approximately 15% of body weight over 68 weeks in the STEP-1 trial. gradual weight management, particularly at higher rates and over extended periods, increases the likelihood of loose or excess skin developing. Mounjaro's dual GIP and GLP-1 mechanism may produce slightly faster initial weight loss than Wegovy's single GLP-1 pathway, though individual results vary significantly.
Loose skin is more likely when weight loss is substantial (typically 10% of body weight or more) and occurs over a shorter timeframe. Both medications achieve this, making skin changes a realistic consideration for many users. The degree of loose skin depends on factors including age, genetics, baseline weight, skin elasticity, and how quickly weight is lost — not solely on which medication you take.
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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.
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Individual Suitability and Prescriber Assessment
Whether Mounjaro or Wegovy is more suitable for you depends entirely on individual health factors, not on loose skin risk alone. Your GP or licensed prescriber will assess your medical history, current health conditions, eligibility criteria (BMI and weight-related health conditions), and medication interactions before recommending either option. You can use our free GLP-1 weight loss calculator to explore potential weight loss projections at different doses, which may help contextualise realistic expectations.
Both medications require a prescription and clinical assessment. Loose skin management — including hydration, strength training, gradual weight loss, and in some cases dermatological advice — should be discussed with your prescriber or GP as part of your overall weight management plan. Neither medication is superior for preventing loose skin; focus instead on working with your healthcare team to choose the medication best suited to your overall health needs.
- 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 direct evidence suggests Mounjaro causes more loose skin than Wegovy. Both medications can result in significant weight loss, which may lead to loose skin depending on individual factors like age, genetics, and how quickly weight is lost. Mounjaro may produce slightly faster weight loss on average in clinical trials, but individual responses vary considerably. Loose skin risk is similar between the two medications.
Can you prevent loose skin whilst taking Mounjaro or Wegovy?
Whilst you cannot completely prevent loose skin during gradual weight management, certain strategies may help: maintain adequate hydration, eat sufficient protein to preserve muscle mass, include strength training to improve skin appearance, and lose weight gradually if possible. Your GP or prescriber can provide personalised advice. Some people benefit from dermatological consultation. Loose skin often improves naturally over time as skin gradually retracts.
What causes loose skin after weight loss?
Loose skin occurs when the skin loses elasticity during gradual weight management. Collagen and elastin fibres don't retract as quickly as body volume decreases. Risk factors include gradual weight management, significant weight loss (10% or more of body weight), older age, genetics, and lower skin elasticity. Both Mounjaro and Wegovy can produce the weight loss rates that increase loose skin risk, though this varies by individual and dose.
Is loose skin a common side effect of Mounjaro?
Loose skin is not listed as a direct side effect of Mounjaro in the product information, as it's a consequence of weight loss rather than the medication itself. However, because Mounjaro supports significant weight loss (average 15–21% in clinical trials), loose skin is a realistic consideration for many users. It's not dangerous, though some people find it cosmetically concerning and may discuss treatment options with their GP.
Should I choose Wegovy over Mounjaro to avoid loose skin?
No — loose skin risk is similar between both medications because both support substantial weight loss. Your choice between Mounjaro and Wegovy should be based on eligibility, overall health suitability, clinical assessment by your prescriber, and your individual circumstances — not on loose skin concerns alone. Both require prescription and clinical assessment. Discuss skin concerns openly with your GP or prescriber when considering either option.
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