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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Mounjaro vs Wegovy — Company, Mechanism & UK Differences
Mounjaro and Wegovy are both prescription-only weight loss injections available in the UK, but they're made by different companies and work in slightly different ways. Mounjaro is manufactured by Eli Lilly and uses a dual GIP and GLP-1 mechanism, while Wegovy is made by Novo Nordisk and uses GLP-1 only. Both are licensed for weight management in UK adults, but understanding how they differ can help your GP or prescriber assess which might suit you best. Individual results vary significantly between people.
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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.
Mechanism, Trials & Dosing Differences
Mechanism of action: Mounjaro (tirzepatide) activates two hormone pathways—both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. This dual action may help regulate appetite and blood sugar control simultaneously. Wegovy (semaglutide) activates GLP-1 only, which signals fullness and slows gastric emptying.
Clinical trial data: SURMOUNT-1 (Mounjaro) showed average weight loss of 15–20.9% body weight over 72 weeks depending on dose. STEP-1 (Wegovy) showed average weight loss of approximately 14.9% body weight over 68 weeks. Both studies involved reduced-calorie diets and increased physical activity—results vary between individuals.
Dosing: Mounjaro starts at 2.5mg weekly and escalates to a maximum of 15mg weekly. Wegovy starts at 0.25mg weekly and reaches a maximum of 2.4mg weekly. Both are once-weekly injections administered as pre-filled pens.
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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 Might Be Right for You — Prescriber Assessment
Both Mounjaro and Wegovy are prescription-only medicines available in the UK through NHS specialist weight management services or private prescribing following a clinical assessment. Your GP or prescriber will evaluate your individual health, medical history, current medications, and eligibility criteria to recommend the most suitable option. Neither medication is assured to work—weight loss depends on adherence, lifestyle changes, and individual metabolism.
Use our free GLP-1 weight loss calculator above to explore potential weight loss projections at different doses. Your prescriber will also consider the side effect profile, cost, and your personal health goals before recommending treatment. Both medications require a reduced-calorie diet and increased physical activity for best results.
- 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 Mounjaro made by a different company than Wegovy?
Yes. Mounjaro (tirzepatide) is manufactured by Eli Lilly and Company. Wegovy (semaglutide) is manufactured by Novo Nordisk. Both are licensed for weight management in UK adults, but they're separate medicines from different pharmaceutical companies with different mechanisms of action.
What's the main difference in how Mounjaro and Wegovy work?
Mounjaro activates two hormone pathways (GIP and GLP-1), while Wegovy activates GLP-1 only. This dual mechanism in Mounjaro may provide slightly different appetite and blood sugar regulation compared to Wegovy's single GLP-1 pathway. Individual response varies significantly.
Which one caused more weight loss in clinical trials?
SURMOUNT-1 trials showed Mounjaro achieved average weight loss of 15–20.9% depending on dose, while STEP-1 trials showed Wegovy achieved approximately 14.9% average weight loss. However, these are trial averages—individual results vary. Your prescriber will advise based on your personal circumstances.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medications requires prescriber guidance. Approximate dose equivalences exist (e.g., 10mg Mounjaro approximates to 1.7mg Wegovy), but this is not an official conversion chart. Any switch must be managed by your GP or specialist to ensure continuity of care.
How do I access Mounjaro or Wegovy in the UK?
Both are available through NHS tier 3 specialist weight management services (via GP referral) or through private prescribing following an online clinical assessment with a UK-licensed prescriber. NHS access varies by region and may involve waiting lists. Your GP can advise on local NHS options.
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.