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 — Which Is Right for You in the UK?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription weight loss injections licensed in the UK, but they work differently and have different dosing schedules. This guide compares them factually so you understand the key differences. Neither is objectively "best" — suitability depends on your individual health, preferences, and prescriber assessment. Both require a prescription following clinical evaluation.
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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) is a dual GIP and GLP-1 receptor agonist — it activates two separate hormone pathways simultaneously. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) both help regulate appetite and blood sugar. This dual mechanism may be why Mounjaro showed higher average weight loss in clinical trials.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates the GLP-1 pathway. The STEP-1 clinical trial showed average weight loss of approximately 14.9% body weight on the maximum dose of 2.4mg over 68 weeks, alongside a reduced-calorie diet and increased physical activity.
SURMOUNT trial data for Mounjaro: Participants on 15mg achieved average weight loss of approximately 20.9% body weight at 72 weeks. Those on 5mg lost approximately 15% on average. Individual results vary significantly — these are clinical trial averages, not assured outcomes.
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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.
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Dosing, Access, and Individual Suitability in the UK
Mounjaro dosing: Starting at 2.5mg, escalated weekly up to a maximum of 15mg once weekly.
Wegovy dosing: Starting at 0.25mg, escalated over 16 weeks to a maximum of 2.4mg once weekly.
Both are available through NHS specialist weight management services or private online prescribing following a clinical assessment. Your prescriber will decide which is more suitable based on your health history, BMI, weight-related conditions, and preferences. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses. Neither medication is assured to work — results depend on adherence, diet, and lifestyle changes alongside the injection.
- 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 more effective than Wegovy?
Clinical trials show Mounjaro achieved higher average weight loss (approximately 20.9% at 15mg) than Wegovy (approximately 14.9% at 2.4mg). However, individual results vary widely. Some people respond better to one than the other. Your prescriber will recommend based on your circumstances, not trial averages alone.
Which injection is available on the NHS in the UK?
Both Mounjaro and Wegovy are approved by NICE for use within NHS specialist weight management services. However, NHS access is through tier 3 specialist services, not standard GP prescription. Availability and waiting times vary significantly by region. Private access is available through online prescribing without NHS referral.
What's the difference between Mounjaro and a weight loss injection like Wegovy?
Mounjaro uses dual GIP+GLP-1 activation (two hormone pathways), while Wegovy uses GLP-1 activation only (one pathway). Mounjaro dosing goes up to 15mg weekly; Wegovy goes up to 2.4mg weekly. Both are once-weekly injections. The dual mechanism may explain Mounjaro's slightly higher trial weight loss, but individual response varies.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications must be managed by your prescriber. There is no official established conversion chart between the two. Your prescriber will assess whether a switch is appropriate and guide you on timing and dosing. Do not change injections without medical guidance.
How do I know which injection is right for me?
Your GP or prescriber will assess your BMI, weight-related health conditions, medical history, and preferences. You can calculate your BMI using our free BMI calculator above. Eligibility typically requires BMI ≥30, or BMI 27–29 with weight-related conditions. Your prescriber will recommend which medication suits you best — it's not about choosing "the best" but the best fit for you personally.
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.