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
Do Stretch Marks Mean Weight Loss?
Stretch marks during weight loss don't necessarily mean you're losing weight effectively — they're a sign of rapid skin changes. Stretch marks (striae) can appear when weight changes quickly, whether you're gaining or losing weight. They form when the skin stretches faster than it can naturally adapt, causing the elastic fibres beneath to tear slightly. On the NHS, stretch marks are considered a normal skin response to rapid body composition changes. Understanding what causes them and when they might appear can help you manage expectations during your weight management journey 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.
What Causes Stretch Marks During Weight Loss?
Stretch marks appear when rapid weight changes force the skin to stretch or compress quickly, faster than the dermis (middle layer) can adapt. This causes tiny tears in the elastic fibres, which heal as visible lines.
- Rate of weight loss matters — faster weight loss increases stretch mark risk
- Genetics play a significant role — some people are naturally more prone to them
- Age and skin elasticity — younger skin typically adapts better than older skin
- Hydration and nutrition — poor skin health during dieting can worsen stretch marks
- Location — most common on stomach, thighs, upper arms, and chest during weight loss
Stretch marks are not a sign that weight loss is working well or poorly — they simply reflect how quickly your body is changing. During NHS weight management and with prescription weight loss medication, stretch marks are an expected skin response for some people. Whether you're managing weight naturally or using GLP-1 weight loss medication, skin changes occur at different rates for everyone.
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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.
Managing and Preventing Stretch Marks
While stretch marks cannot be completely prevented, several steps may reduce their severity:
- Gradual weight loss — aiming for 0.5–1 kg per week (the NHS recommendation) gives skin time to adapt
- Stay hydrated — drink plenty of water to support skin elasticity
- Moisturise regularly — products containing cocoa butter or vitamin E may help skin flexibility
- Eat balanced nutrition — protein and vitamins support skin health during weight loss
- Avoid rapid weight changes — yo-yo dieting increases stretch mark risk significantly
If stretch marks are causing concern, your GP can discuss treatments available on the NHS, including referral to dermatology services. Remember that stretch marks fade naturally over time — they typically appear red or purple initially, then fade to silvery or white lines over months.
- 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.
Are stretch marks a sign that weight loss is working?
No. Stretch marks indicate rapid skin changes, not weight loss success. They can appear during any quick body composition change. Slow, steady weight loss (0.5–1 kg weekly, as NHS recommends) is often healthier and may reduce stretch marks. Use our free BMI calculator to check your progress and track changes at a healthy pace.
Will stretch marks disappear after weight loss?
Yes, most stretch marks fade over time. Initially red or purple, they gradually become silvery or white and become less noticeable. Complete disappearance varies — some fade significantly, others remain visible. Your GP can discuss treatment options like microdermabrasion or laser therapy if you're concerned about appearance.
Can weight loss medication like Mounjaro or Wegovy cause stretch marks?
Weight loss medications don't directly cause stretch marks, but gradual weight management from any source can trigger them. GLP-1 medications may produce faster results than diet alone, which increases stretch mark risk for some people. Weight loss at a steady, sustainable rate minimises this risk regardless of the method used.
How can I prevent stretch marks during weight loss?
Prevent stretch marks by losing weight gradually (0.5–1 kg weekly), staying hydrated, moisturising skin regularly, and eating balanced nutrition with adequate protein. Avoid extreme calorie restriction or rapid weight changes. Genetics also play a role — some people are naturally more prone to stretch marks regardless of prevention efforts.
Should I see my GP about stretch marks during weight loss?
Stretch marks are normal and harmless, so routine GP visits aren't necessary. However, mention them during regular appointments, especially if you notice signs of infection, unusual colour changes, or if they're causing significant distress. Your GP can discuss NHS treatment options or refer you to dermatology if needed.
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.