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 for Weight Loss in Non-Diabetics: Wegovy vs Mounjaro
Both semaglutide (Wegovy) and tirzepatide (Mounjaro) are prescription-only weight loss injections approved in the UK for non-diabetic adults. While often compared, they work differently and suit different people. Semaglutide is a GLP-1 receptor agonist licensed for weight management by Novo Nordisk. Understanding how these two weekly weight loss injections differ — in mechanism, trial results, and eligibility — helps you and your GP assess which may be suitable for your individual health needs.
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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 Semaglutide and Tirzepatide Work Differently
Semaglutide (Wegovy) activates a single hormone pathway: GLP-1 (glucagon-like peptide-1). This suppresses appetite, increases feelings of fullness, and slows stomach emptying. Clinical trials (the STEP programme) showed semaglutide 2.4mg led to average weight loss of approximately 14.9% of body weight over 68 weeks in non-diabetic adults alongside reduced-calorie diet and physical activity.
Tirzepatide (Mounjaro) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways simultaneously. This dual mechanism may provide additional metabolic effects. SURMOUNT clinical trials showed tirzepatide 15mg achieved average weight loss of approximately 20.9% of body weight over 72 weeks, also with lifestyle changes.
- Semaglutide: single mechanism (GLP-1 only)
- Tirzepatide: dual mechanism (GIP + GLP-1)
- Both: once-weekly injections, prescription-only, require clinical assessment
Individual results vary significantly — trial averages are not assured outcomes for any person.
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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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Side Effects, Suitability, and Getting Treatment in the UK
Both medications cause similar common side effects: nausea, diarrhoea, constipation, and stomach pain — usually most pronounced when starting and typically improve over time. Rare serious risks include pancreatitis and gallbladder complications.
For non-diabetic adults in the UK, eligibility is based on BMI: 30 or above, or 27+ with weight-related health conditions (high blood pressure, dyslipidaemia, sleep apnoea, or cardiovascular history). Your GP or a licensed prescriber will assess which medication is clinically appropriate based on your health profile, medical history, and preferences. Try our free GLP-1 weight loss calculator above to explore potential outcomes, and use the BMI calculator to check your current category.
- 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 (Wegovy) or tirzepatide (Mounjaro) better for weight loss?
Neither is universally "better" — results vary by individual. Clinical trials showed tirzepatide achieved slightly higher average weight loss (≈21% vs ≈15%), but semaglutide is also highly effective. Your prescriber will assess which suits your health needs, medical history, and preferences. Individual response varies significantly.
How long does semaglutide take to work for weight loss in non-diabetics?
Most people notice appetite reduction within days to weeks, but meaningful weight loss typically takes 4–8 weeks to become apparent. Clinical trials measured results over 68 weeks. Sustainable weight loss requires consistent use alongside reduced-calorie diet and increased physical activity.
Can I switch from semaglutide to tirzepatide or vice versa?
Yes, but only under prescriber guidance. Approximate dose equivalences exist (semaglutide 0.5mg ≈ tirzepatide 5mg), but any switch must be managed individually. Your GP or prescriber will assess whether a change is appropriate for you.
Do I need a GP referral to get semaglutide (Wegovy) for weight loss in the UK?
Not necessarily. NHS access requires GP referral to specialist tier 3 services, but availability varies by region and waiting lists are long. Private access is available through UK-licensed prescribers following an online clinical assessment — no NHS referral needed.
Does semaglutide work if I'm not diabetic?
Yes. Semaglutide (Wegovy) is licensed specifically for weight management in non-diabetic adults. GLP-1 receptors control appetite and satiety regardless of diabetes status. Clinical trials (STEP programme) tested Wegovy in non-diabetic populations and showed significant weight loss results.
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.