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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Semaglutide Weight Loss: Real Results and NHS Context
Semaglutide (brand name Wegovy) is a prescription-only weekly injection that has shown genuine weight loss results in UK clinical trials, but individual outcomes vary significantly. This guide explains what the evidence actually shows, how NHS eligibility works in the UK, and the real difference between "before and after" expectations based on STEP trial data rather than marketing claims. Use our free GLP-1 weight loss calculator above to explore potential outcomes at different doses.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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 the NHS-Approved STEP Trials Actually Showed
The STEP-1 clinical trial, which supports Wegovy's UK approval, followed 1,961 adults for 68 weeks. Participants taking semaglutide 2.4 mg (the maximum dose) lost an average of 14.9% of their body weight — roughly 15 kg for someone starting at 100 kg. However, this was alongside a reduced-calorie diet and increased physical activity. Some participants lost significantly more; others lost less. The trial included people with BMI 27 or above with weight-related health conditions, matching NHS eligibility criteria.
- Average weight loss: 14.9% body weight at 68 weeks on 2.4 mg semaglutide
- Comparison: Placebo group lost 2.6% on average
- Important context: Individual results ranged from minimal loss to 20%+ loss
- Duration: Results achieved over approximately 16 months with continuous treatment
- Maintenance: Weight loss was maintained only while continuing the weekly injection
These are real clinical trial results, not before/after marketing images. Results depend heavily on adherence to diet, activity level, dose tolerance, and individual metabolism.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
NHS Eligibility and Prescribing in UK Tier 3 Services
In the UK, semaglutide (Wegovy) is available through NHS specialist tier 3 weight management services following GP referral, and through private online prescribing. NHS access requires a BMI of 30 or above, or 27–29.9 with weight-related conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds (27.5+). NHS waiting lists for specialist services can be months or longer depending on your region. Private prescribing is faster but involves out-of-pocket costs. Use our free BMI calculator above to check your starting point, then discuss NHS referral options with your GP.
NICE (National Institute for Health and Care Excellence) has approved semaglutide for use within NHS weight management services, positioning it as part of a structured support programme rather than a standalone prescription. The weekly weight loss injection is typically initiated at 0.25 mg and escalated gradually to the 2.4 mg maintenance dose over approximately 16–20 weeks. Before/after expectations should always include the reality that semaglutide works best with lifestyle changes — diet and activity matter just as much as the medication itself. Track your progress with our free progress tracker once you start any weight loss journey.
- 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.
Is semaglutide the same as Ozempic?
Both contain the same drug, but Ozempic (up to 2 mg) is approved for type 2 diabetes management. Wegovy (up to 2.4 mg) is the licensed weight management version in the UK. Using Ozempic for weight loss would be off-label and not recommended. Always ensure you are prescribed the correct product for your clinical need.
What's a realistic before and after weight loss timeline with semaglutide?
Clinical trials show weight loss begins within 4–8 weeks on semaglutide, with most loss occurring between weeks 8–20. Average maximum weight loss takes 16–20 weeks to reach. Some people plateau after 6 months; others continue losing if the dose is increased or lifestyle changes continue. Individual timelines vary.
Does weight come back after stopping semaglutide?
Clinical data shows weight regain if semaglutide is stopped and lifestyle changes are not maintained. The STEP trials did not measure long-term post-treatment outcomes, but weight loss injections are typically intended as ongoing treatment, not short-term courses.
How much does semaglutide cost on the NHS vs private in the UK?
NHS cost is covered (no direct charge), but availability depends on your region and specialist tier 3 services. Private semaglutide costs approximately £130–£320 per month depending on dose and provider. Always obtain a prescription from a UK-licensed prescriber.
What percentage of people actually lose weight with semaglutide?
In STEP trials, approximately 70% of participants on semaglutide 2.4 mg achieved at least clinically studied weight loss compared to 20% on placebo. About 50% achieved 10% or more weight loss. However, not everyone responds equally, and results depend on adherence, diet, activity, and individual factors.
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.