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
Free tracker included with every download this week
How Does Mounjaro Work Compared to Wegovy?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both prescription-only weight management injections licensed in the UK, but they work in different ways. Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 receptor agonist only. Understanding how each works can help you and your GP decide which might be more suitable for your individual circumstances. Both require a clinical assessment before prescription and are used alongside reduced-calorie diet and increased physical activity for best results.
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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 Differences: GLP-1 Only vs Dual GIP and GLP-1
Wegovy (semaglutide) activates the GLP-1 receptor pathway alone. This signals to your brain that you are full, reduces appetite and food cravings, and slows how quickly food leaves your stomach. Clinical trial data from STEP-1 showed an average weight loss of approximately 14.9% of body weight over 68 weeks at the maximum dose of 2.4 mg.
Mounjaro (tirzepatide) activates two pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. This dual mechanism may provide additional appetite suppression and potentially greater weight loss than GLP-1 alone. SURMOUNT-1 clinical trial data showed average weight loss of approximately 20.9% of body weight over 72 weeks at the maximum dose of 15 mg.
Both slow gastric emptying and help regulate appetite, but Mounjaro's dual mechanism may offer additional metabolic effects. However, individual results vary significantly — these are clinical trial averages, not assured outcomes for all users.
Clinically BackedWeight Loss
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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.
Clinical Trial Data and Eligibility: Which Might Be Right for You?
Both medications are eligible for UK prescription if you have a BMI of 30 kg/m² or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease. Use our free BMI calculator above to check your starting point. Wegovy requires once-weekly injections with doses ranging from 0.25 mg to 2.4 mg, whilst Mounjaro uses once-weekly injections from 2.5 mg to 15 mg. Neither is superior — your prescriber will assess your individual health, medical history, and preferences to recommend which is appropriate for you. Both require a clinical assessment through either NHS specialist weight management services or a private licensed prescriber.
- 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 in how Mounjaro and Wegovy work?
Wegovy is a GLP-1 receptor agonist (single pathway), whilst Mounjaro is a dual GIP and GLP-1 agonist (two pathways). The dual mechanism may provide additional appetite suppression and metabolic effects, though individual responses vary. Both slow stomach emptying and reduce hunger signals to the brain.
Which caused more weight loss in clinical trials?
In SURMOUNT-1, Mounjaro showed an average clinically studied weight loss at 15 mg (72 weeks). In STEP-1, Wegovy showed an average clinically studied weight loss at 2.4 mg (68 weeks). However, these are trial averages with lifestyle changes included — real-world results vary significantly between individuals.
Are both available on the NHS in the UK?
Both Mounjaro and Wegovy are UK-licensed and can be prescribed through NHS tier 3 specialist weight management services, though availability varies by region and waiting lists can be lengthy. Both are also available privately through UK-licensed prescribers following online assessment.
How do I know which one my GP would recommend?
Your prescriber will consider your medical history, current medications, preferences, and any previous experiences with weight loss treatments. Neither is universally "better" — suitability is individual. A licensed prescriber will assess whether either is appropriate for you.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official established dose conversion — your prescriber will assess the appropriate approach if you wish to switch, which typically involves stopping one and titrating the other separately.
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.