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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Does Wegovy Work The Same As Mounjaro?
Wegovy and Mounjaro are both prescription-only weight loss injections available in the UK, but they do not work in exactly the same way. While both activate GLP-1 hormone pathways to reduce appetite, tirzepatide (Mounjaro) uses a dual GIP and GLP-1 mechanism, whereas semaglutide (Wegovy) activates GLP-1 alone. This fundamental difference in how they work means individual results vary, and suitability depends on your personal health profile and prescriber assessment. This guide explains the key differences to help you understand both options.
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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 Wegovy And Mounjaro Work Differently
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates a single hormone pathway that signals to your brain that you're full, slows stomach emptying, and helps regulate blood sugar. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. This dual mechanism may provide additional appetite suppression compared to GLP-1 alone, though clinical trial data shows both medications produce meaningful weight loss.
- Wegovy: Single GLP-1 pathway activation
- Mounjaro: Dual GIP + GLP-1 pathway activation
- Both: Reduce hunger, slow gastric emptying, support weight loss alongside diet and exercise
Clinical trials (STEP for Wegovy, SURMOUNT for Mounjaro) demonstrated that both medications help participants lose approximately 15–21% of body weight on average — though individual results vary significantly. Neither assures a specific weight loss amount.
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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
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Clinical Trial Data And Dosing Differences
In the STEP-1 trial, Wegovy (semaglutide) at maximum dose (2.4 mg weekly) achieved average weight loss of approximately 14.9% over 68 weeks. In SURMOUNT-1, Mounjaro (tirzepatide) at 15 mg weekly achieved approximately 20.9% average weight loss over 72 weeks. However, these are clinical trial averages — your personal response depends on genetics, lifestyle, diet adherence, and overall health.
Dosing also differs: Wegovy escalates from 0.25 mg to a maximum of 2.4 mg weekly, while Mounjaro starts at 2.5 mg and escalates to 15 mg weekly. Both require a minimum of 4 weeks on each dose before increasing. Your prescriber will determine the right dose for you based on tolerability and clinical response.
- 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.
Which is more effective — Wegovy or Mounjaro?
Clinical trials suggest Mounjaro may produce slightly greater average weight loss (approximately 21% vs 15%), but both are effective. Individual results vary significantly, and neither assures specific outcomes. Your prescriber will assess which is suitable for your health profile.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications is possible but must be managed by your prescriber. Approximate dose equivalences exist (for example, 2.4 mg Wegovy is roughly equivalent to 15 mg Mounjaro), but any switch requires clinical oversight and monitoring.
Are the side effects the same for both medications?
Both commonly cause nausea, diarrhoea, vomiting, and constipation, particularly during dose escalation. However, individual tolerance varies. Your prescriber will monitor you and adjust dosing if side effects are problematic.
How do I know which medication my prescriber will recommend?
Your prescriber will consider your BMI, health conditions, previous medication tolerance, and personal preference. Both are prescription-only, licensed for weight management in UK adults with a BMI of 30+ (or 27+ with weight-related conditions). Ask your prescriber about suitability for your circumstances.
Can I use the UK weight conversion or BMI calculator to compare my eligibility for both?
Yes. Use our free BMI calculator above to check your current BMI — this determines eligibility for prescription weight loss treatment. Both Wegovy and Mounjaro require a BMI of 30 or above (or 27+ with qualifying health conditions) to be considered by a prescriber.
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.