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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What Does Wegovy Do? How Semaglutide Works for Weight Management
Wegovy is a prescription-only, once-weekly injection containing semaglutide that helps support weight management in UK adults. It works by activating the GLP-1 receptor — a natural hormone pathway in your body that helps control appetite, food cravings, and how full you feel after eating. Clinical trials showed that Wegovy helped people lose an average of around 15% of their body weight when combined with a reduced-calorie diet and increased physical activity. This guide explains exactly what Wegovy does, how it works in your body, and what the evidence tells us about its effectiveness.
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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.
How Wegovy Works — The GLP-1 Mechanism
Wegovy contains semaglutide, which is a GLP-1 receptor agonist — this means it mimics and amplifies the effects of glucagon-like peptide-1, a natural hormone your body produces in the gut after eating.
When you take Wegovy, it works in several ways:
- Appetite reduction: Signals to your brain that you feel fuller, helping reduce hunger and food cravings
- Portion control: Helps you feel satisfied after eating smaller meals
- Gastric emptying: Slows how quickly food leaves your stomach, prolonging the feeling of fullness
- Blood sugar regulation: Helps your body manage glucose levels more effectively
Unlike insulin, Wegovy does not directly lower blood sugar — it works through the appetite and satiety centres of your brain. The appetite-suppressing effects are typically most noticeable in the first few weeks and may stabilise as your body adjusts to each dose.
Clinically BackedWeight Loss
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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.
Clinical Evidence — What the STEP Trials Showed
The effectiveness of Wegovy is based on the STEP clinical trials, which tested semaglutide 2.4 mg (the maximum Wegovy dose) in UK and international adults with obesity or overweight with health conditions.
Key findings from STEP-1:
- Average weight loss: approximately 14.9% of body weight at 68 weeks on 2.4 mg
- Results achieved alongside a reduced-calorie diet and increased physical activity
- Individual results vary significantly — some people lost more, some less
- Weight loss was sustained while taking the injection; weight loss tends to slow or stabilise after the first year
Important: These are clinical trial averages and do not assures individual outcomes. Your GP or prescriber can discuss realistic expectations for you personally. Try our GLP-1 weight loss calculator to see projected results at different Wegovy doses.
- 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 Wegovy the same as Ozempic?
Both contain semaglutide, but they are different medicines. Ozempic is approved for type 2 diabetes (doses up to 2 mg) and is not licensed for weight loss in the UK. Wegovy is specifically licensed for weight management at a higher dose (up to 2.4 mg). Using Ozempic for weight loss would be off-label. Always ensure you are prescribed Wegovy if weight management is your goal.
How quickly does Wegovy start to work?
Most people notice appetite reduction within 1–2 weeks of starting Wegovy. However, noticeable weight loss typically takes 4–8 weeks. The full effect builds gradually as your dose increases over 16 weeks. Weight loss continues over months, with most significant loss seen in the first 3–6 months of treatment.
Do you need to diet and exercise while taking Wegovy?
Yes. Wegovy works best alongside a reduced-calorie diet and increased physical activity. Clinical trials showed results were achieved with these lifestyle changes combined. Wegovy supports these efforts by reducing hunger and cravings, but it is not a replacement for healthy eating and movement. Your prescriber will discuss this with you.
What's the difference between Wegovy and Mounjaro?
Wegovy (semaglutide) is a single GLP-1 agonist. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist — it activates two hormone pathways instead of one. Clinical trials suggest Mounjaro may produce slightly higher average weight loss (~20.9% vs ~14.9%), but individual results vary. Both are prescription-only and require clinical assessment. Your prescriber will advise which is suitable for you.
What happens to weight after stopping Wegovy?
If you stop taking Wegovy, the appetite-suppressing effects wear off within days to weeks. Weight loss is typically not maintained without continued treatment or sustained lifestyle changes. Some people maintain loss through diet and exercise alone; others regain weight gradually. Your prescriber will discuss long-term plans with you before starting treatment.
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.