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 5mg vs Wegovy — What's the Difference?
Both Mounjaro and Wegovy are prescription-only weekly weight loss injections available in the UK, but they work differently. Mounjaro contains tirzepatide (a dual GIP and GLP-1 receptor agonist), whilst Wegovy contains semaglutide (a GLP-1 receptor agonist only). At the 5mg dose, Mounjaro is typically used as a maintenance or escalation dose, whereas Wegovy's strongest single dose is 2.4mg. This comparison guide explains the key differences, trial data from SURMOUNT and STEP studies, and how your prescriber decides which is right for you. Use our free GLP-1 weight loss calculator to explore potential outcomes with either medication.
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Calculate Your BMI Instantly
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.
Clinical Trial Data and Mechanism Differences
Mechanism of action: Mounjaro activates two hormone pathways—GIP (glucose-dependent insulinotropic polypeptide) and GLP-1—giving it a dual mechanism. This combination may help regulate appetite, reduce cravings, and slow gastric emptying. Wegovy activates GLP-1 alone, which also reduces appetite and supports feeling fuller after meals, but through a single pathway.
SURMOUNT vs STEP trial outcomes: In the SURMOUNT-1 trial, participants on Mounjaro 15mg (the maximum dose) achieved an average weight loss of approximately 20.9% of body weight over 72 weeks. The STEP-1 trial showed Wegovy 2.4mg (its highest dose) delivered average weight loss of approximately 14.9% over 68 weeks. However, individual results vary significantly. At the 5mg Mounjaro dose specifically, average weight loss was approximately 15% in trials—similar to Wegovy's results.
- Mounjaro: dual GIP+GLP-1 mechanism, up to 15mg weekly
- Wegovy: single GLP-1 mechanism, up to 2.4mg weekly
- Both require a reduced-calorie diet and increased physical activity for best results
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.
Which Medication Is Right for You?
Neither Mounjaro nor Wegovy is "better"—the right choice depends on your individual health profile, medical history, and how your body responds. Your GP or a licensed prescriber will assess you during a clinical consultation to decide eligibility and suitability. Both are prescription-only medicines requiring a clinical assessment. Some people respond better to one mechanism than the other; this is individual variation, not superiority of one drug. If you start on one and it doesn't work well, switching to the other under medical guidance is possible. Both medications may cause similar side effects (nausea, constipation, diarrhoea) and both require careful injection technique and storage. Try our BMI calculator to understand your starting point, then discuss options with your 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.
At 5mg, is Mounjaro more effective than Wegovy?
No. Clinical data shows Mounjaro 5mg achieves similar average weight loss (around 15%) to Wegovy 2.4mg (around 14.9%). However, individual results vary. Neither medication assures specific weight loss—effectiveness depends on adherence, diet, exercise, and personal metabolism.
Why does Mounjaro go up to 15mg if Wegovy only goes to 2.4mg?
The doses aren't directly comparable because Mounjaro is a dual GIP+GLP-1 agonist whilst Wegovy is GLP-1 only. The dual mechanism may allow higher doses whilst maintaining tolerability. Both medications start low and escalate over weeks under prescriber guidance.
Can I switch from Mounjaro 5mg to Wegovy or vice versa?
Potentially, yes—but any switch must be managed by your prescriber. Approximate conversions exist (5mg Mounjaro ≈ 0.5mg Wegovy), but there's no official established conversion chart. Your prescriber will assess whether switching is appropriate and how to transition safely.
What are the main side effects at the 5mg Mounjaro dose?
Common side effects include nausea, constipation, diarrhoea, and stomach pain. These often ease over time as your body adjusts. Serious side effects are rare but may include severe stomach pain (possible pancreatitis) or gallbladder issues—seek immediate help if these occur.
How do I access Mounjaro or Wegovy in the UK?
Both require a prescription from a UK-licensed prescriber following a clinical assessment. You can access via NHS specialist weight management services (requires GP referral) or private online consultations. Both routes check your eligibility based on BMI, weight-related health conditions, and medical history.
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.