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 Before and After Weight Loss
Stretch marks are a common concern during and after weight loss, but understanding what causes them and how your skin responds can help you manage expectations. Whether you're losing weight through lifestyle changes, prescription weight management medication like Wegovy, or other methods, your skin will go through changes. The good news is that stretch marks often fade significantly over time, though complete disappearance isn't always assured. This guide explains what happens to your skin during weight loss and what you can realistically expect.
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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 Stretch Marks Form and What Happens During Weight Loss
Stretch marks form when the dermis (middle layer of skin) tears as your skin stretches rapidly during weight gain. The tears allow blood vessels and collagen fibres underneath to show through, creating the reddish or purplish marks you see. During weight loss, the opposite process occurs—your skin gradually shrinks and tightens, but the stretched collagen fibres take time to repair and remodel.
What happens to existing stretch marks:
- Colour changes: Red or purple marks (newer stretch marks) typically fade to white or silver over 12–24 months as inflammation reduces and blood vessels constrict
- Texture: Stretch marks remain slightly indented because the collagen hasn't fully regenerated, though they become less noticeable over time
- Timeline: Most visible fading occurs within the first year after weight loss stabilises, though improvement can continue for years
- Individual variation: Skin elasticity, age, genetics, and how quickly you lost weight all affect how much your marks fade
If you're considering prescription weight loss medication through NHS weight management services or private prescribing, the rate of weight loss may influence stretch mark appearance—more gradual loss may allow better skin adaptation.
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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.
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Managing Stretch Marks and Skin Health During Weight Loss
While you cannot completely erase stretch marks, several approaches can support skin health and potentially improve their appearance during weight loss. Staying hydrated, eating adequate protein, and maintaining regular physical activity all support collagen production and skin elasticity. Some people find that moisturising with products containing retinol, vitamin C, or centella asiatica may help during the fading process, though evidence is modest.
For weight loss journeys—whether through lifestyle changes, GLP-1 weight loss injections, or other methods—maintaining a steady, sustainable rate of weight loss (around 0.5–1 kg per week according to NHS guidance) gives your skin more time to adapt and may result in better skin appearance overall. Track your progress using free tools to monitor both weight loss and how your skin responds over time. If stretch marks remain very distressing after 12–18 months of stable weight, treatments like laser therapy or microdermabrasion are available through private clinics, though these should be discussed with your GP first.
- 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 completely disappear after weight loss?
Complete disappearance is rare. Most stretch marks fade significantly over 12–24 months, turning from red or purple to white or silver. They typically remain slightly visible but become much less noticeable. Individual results depend on age, genetics, skin elasticity, and how quickly you lost weight.
How long does it take for stretch marks to fade?
The fastest fading occurs within the first 12 months after weight loss stabilises. Colour changes happen first (red to white), usually within 6–12 months. Texture improvement continues longer, sometimes over several years. Patience is key—the process is gradual but generally improves steadily.
Can I prevent stretch marks during weight loss?
You cannot completely prevent them if you're genetically predisposed, but you can minimise severity. Lose weight gradually (0.5–1 kg per week), stay hydrated, eat adequate protein, exercise regularly, and moisturise your skin. Avoiding gradual weight management gives your skin more time to adapt.
Are stretch marks from weight loss different from other stretch marks?
No—stretch marks from weight loss are identical to those from weight gain, pregnancy, or rapid muscle growth. They form the same way (collagen tears) and fade through the same process. Management and fading timelines are also the same regardless of cause.
Should I wait for stretch marks to fade before or after weight loss?
Stretch marks fade best after your weight has stabilised, so don't delay starting your weight management journey. Continue with your sustainable weight loss plan—whether through lifestyle changes or prescription weight management—and let your skin adapt at its own pace alongside your weight loss.
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.