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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Is Wegovy and Mounjaro the Same?
Wegovy and Mounjaro are both prescription-only weight loss injections available in the UK, but they are not the same medicine. While both can help with weight management, they use different mechanisms of action, have different dose ranges, and may suit different individuals. Your prescriber will assess which is more appropriate for you based on your personal health profile and 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.
Key Differences Between Wegovy and Mounjaro
Mechanism of action: Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in your body. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. This dual mechanism in Mounjaro may contribute to why clinical trials showed slightly higher average weight loss results.
Manufacturer and dose range: Mounjaro is made by Eli Lilly and ranges from 2.5 mg to 15 mg weekly. Wegovy is made by Novo Nordisk and ranges from 0.25 mg to 2.4 mg weekly. Mounjaro's higher maximum dose reflects its different formulation.
Clinical trial data: SURMOUNT-1 trials for Mounjaro showed average weight loss of approximately 15–21% of body weight. STEP-1 trials for Wegovy showed approximately 15% average weight loss. Both results were achieved alongside reduced-calorie diet and increased physical activity—individual results vary significantly.
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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.
Which Is Right for You—Prescriber Assessment
Neither Mounjaro nor Wegovy is inherently "better"—suitability depends on your individual health circumstances, medical history, and how your body responds to treatment. Both require a clinical assessment from a UK-licensed prescriber before prescription. Try our free GLP-1 weight loss calculator above to understand potential outcomes at different doses, and use the BMI calculator to confirm your eligibility starting point. Your prescriber may recommend one over the other based on factors including your current health conditions, other medications you take, and your previous response to similar treatments. Some individuals may respond better to the dual mechanism of Mounjaro, whilst others achieve excellent results with Wegovy's single GLP-1 pathway.
- 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.
What does "GLP-1 receptor agonist" mean?
GLP-1 stands for glucagon-like peptide-1, a natural hormone your body produces after eating that signals fullness. A GLP-1 receptor agonist medication mimics this hormone, helping reduce appetite and support feeling fuller on smaller portions. Wegovy works this way. Mounjaro does this plus activates another pathway (GIP), giving it a dual mechanism.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, switching between these medications is possible but must be managed by your prescriber. There is no official UK conversion chart—approximate equivalences exist (for example, Wegovy 2.4 mg is roughly equivalent to Mounjaro 15 mg), but any switch requires a clinical discussion and new prescription. Never switch without medical guidance.
Is Mounjaro more effective than Wegovy?
Clinical trials suggest Mounjaro produced slightly higher average weight loss, but both deliver meaningful results. "More effective" varies by individual—some people respond better to one than the other. Your prescriber will consider your specific situation. Results depend on adherence, diet, activity, and individual metabolism, not just the medication choice.
Are both available on the NHS in the UK?
NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use, but availability varies significantly by region and NHS trust. Access is typically through specialist tier 3 weight management services. Waiting lists can be lengthy. Both are available privately through UK-licensed prescribers without NHS referral.
What if I'm allergic to one—can I take the other?
Both medications are peptide-based and have some shared ingredients, so allergy to one may mean caution with the other. However, they are distinct molecules. Always inform your prescriber of any previous allergic reactions. They will assess whether the alternative is safe for you based on the specific allergen involved.
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.