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 Mounjaro or Wegovy Better for Weight Loss?
Both Mounjaro and Wegovy are prescription-only weight loss injections licensed in the UK, but they work differently and suit different people. The straightforward answer is: neither is objectively "better" — which one is more suitable depends on your individual health, medical history, and how your body responds. Clinical trials show both can support meaningful weight loss when used alongside a reduced-calorie diet and increased physical activity. Your GP or a licensed prescriber will assess which is appropriate for you following a clinical assessment.
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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 Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) uses a dual mechanism: it activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptor pathways. This dual action may help regulate appetite and food cravings more intensively.
Wegovy (semaglutide) activates only the GLP-1 pathway. Clinical trials show both medications support weight loss through similar effects: reduced appetite, increased feeling of fullness, and slowed gastric emptying. In the SURMOUNT-1 trial, Mounjaro at the maximum 15 mg dose resulted in average weight loss of approximately 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy at 2.4 mg achieved average weight loss of approximately 14.9% at 68 weeks. However, individual results vary significantly — these are trial averages, not assured outcomes. Both require prescription and clinical assessment for eligibility.
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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 Decision
Neither medication is objectively "better" — suitability depends on factors only a prescriber can assess: your current health conditions, medications, medical history, and personal circumstances. Some people respond better to dual-mechanism GIP+GLP-1 activation (Mounjaro), whilst others achieve excellent results with GLP-1 alone (Wegovy). Your prescriber will consider your BMI, any weight-related health conditions, contraindications, and previous treatment responses. Use our GLP-1 weight loss calculator to explore potential weight loss projections, then discuss both options with your GP or licensed prescriber. Both medications are available through NHS specialist weight management services (with variable waiting times by region) or through private online prescribing following a clinical assessment.
- 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's the main difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro's dual mechanism may offer a different appetite-suppression profile, but both support weight loss through similar overall effects: reduced hunger, increased fullness, and slower stomach emptying.
Which one works better for weight loss?
Clinical trials show Mounjaro achieved slightly higher average weight loss (approximately 20.9% at maximum dose) compared to Wegovy (approximately 14.9%), but individual results vary greatly. Your prescriber will recommend based on your personal health factors, not trial averages. Neither is assured to work better for you specifically.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, switching is possible, but only under prescriber guidance. There is no official conversion chart between the two medications. Any switch requires a new clinical assessment and careful dose management. Never self-switch between prescription medications — always consult your prescriber.
Which is available on the NHS?
Both Mounjaro and Wegovy are available through NHS tier 3 specialist weight management services, though availability and waiting times vary significantly by region. Private prescribing is available for both through GPhC-registered online pharmacies following a clinical assessment.
What if one doesn't work for me?
If you don't see results or experience intolerable side effects with one medication, your prescriber may adjust the dose, extend the trial period, or discuss switching to the other medication. Weight loss medication works best alongside dietary changes and increased physical activity — medication alone is not a complete solution.
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.