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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Stretch Marks After Weight Loss: What You Need to Know
Stretch marks are a common concern after significant weight loss, whether through diet, exercise, or prescription weight management medication. They occur when skin stretches rapidly and the dermis (deeper skin layer) tears, leaving visible marks. Whilst they're not harmful, understanding how they form and what options exist can help you feel more confident about your body after weight loss. This guide explains the science behind stretch marks and explores both prevention and treatment approaches available in the UK.
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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.
Why Stretch Marks Form During Weight Loss
Stretch marks develop when rapid weight changes force your skin to stretch or shrink faster than it can naturally adapt. Your skin contains collagen and elastin fibres that provide elasticity; when these are overstretched, microscopic tears form in the dermis, the layer beneath the outer skin. This creates the characteristic red, purple, or silvery lines you see.
- gradual weight management — faster losses (over 1kg per week) increase stretch mark risk compared to gradual weight loss at 0.5kg per week
- Age and genetics — younger skin is generally more elastic, but genetic predisposition is the strongest predictor of whether you'll develop stretch marks
- Skin hydration — well-hydrated skin stretches more effectively; dehydration increases fragility
- Weight loss magnitude — larger total weight losses increase likelihood, particularly when using weight management UK services or prescription weight loss medication
Importantly, stretch marks are not a sign that weight loss was unhealthy — they're simply a normal physiological response to significant body composition change.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Prevention and Management Strategies
Whilst you cannot completely prevent stretch marks if you're genetically predisposed, several strategies may reduce their severity. Maintain gradual weight loss — the NHS recommends losing 0.5 to 1kg per week for sustainable results that give your skin time to adapt. Stay hydrated (aim for 6–8 glasses daily), use moisturisers rich in glycerin or hyaluronic acid, and consider products containing retinol or vitamin C, which support collagen production. If using GLP-1 weight loss medication or other prescription weight loss approaches, consistent progress tracking helps you monitor both weight and skin changes. Try our free progress tracker to log your journey and notice patterns 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.
Do stretch marks fade completely after weight loss?
Stretch marks do fade naturally over time, transitioning from red or purple to pale silver or white. Most fade significantly within 6–12 months. However, they rarely disappear entirely. Newer marks (red/purple) respond better to treatment than older ones (white/silver).
Can prescription weight loss medication cause more stretch marks?
Weight loss from any source — diet, exercise, or GLP-1 medication like semaglutide — can cause stretch marks if weight loss is rapid. The mechanism is the same: skin stretching. Slower, steady weight loss reduces risk regardless of method.
What medical treatments are available for stretch marks in the UK?
The NHS may offer laser therapy, microdermabrasion, or radiofrequency treatments depending on your location and NHS availability. Private treatments include chemical peels, microneedling, and laser resurfacing. Discuss options with your GP to understand what's available in your area.
Does moisturiser really help prevent stretch marks?
Moisturising helps keep skin hydrated and supple, which supports elasticity during weight changes. Whilst it won't eliminate risk (genetics plays the largest role), good skin hydration and products containing retinol or vitamin C may reduce severity.
Are stretch marks from weight loss the same as pregnancy stretch marks?
The mechanism is identical — rapid skin stretching causes dermis tears. However, pregnancy stretch marks often appear lower on the abdomen, whilst weight loss stretch marks tend to appear where fat deposits were largest. Treatment options are the same.
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.