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 Prescribing Guidelines vs Wegovy
Understanding the prescribing guidelines for Mounjaro and Wegovy helps explain how healthcare professionals decide which weight loss medication may be appropriate for individual patients in the UK. Both are prescription-only injectables licensed for weight management, but they differ in mechanism, dosing schedules, and clinical evidence. This guide clarifies the key differences GPs and specialist prescribers consider when assessing eligibility and suitability.
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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 Mechanisms and Trial Evidence
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways. Clinical trials (SURMOUNT-1) showed average weight loss of approximately 15–21% of body weight at the maximum 15 mg dose over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. The STEP-1 clinical trial demonstrated average weight loss of approximately 14.9% at the maximum 2.4 mg dose over 68 weeks under similar lifestyle conditions.
- Mounjaro: dual mechanism may offer slightly higher average weight loss in trials
- Wegovy: single mechanism, longer clinical track record in weight management
- Both: individual results vary significantly; trial averages do not predict personal outcomes
Your prescriber will assess which mechanism may be more suitable for your specific health profile and medical history.
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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 Schedules and UK Prescribing Practice
Mounjaro dosing: starts at 2.5 mg once weekly, escalates every 4 weeks through 5 mg, 7.5 mg, 10 mg, 12.5 mg, to a maximum of 15 mg once weekly. Total treatment duration varies by individual response.
Wegovy dosing: begins at 0.25 mg weekly, escalates to 0.5 mg, 1 mg, 1.7 mg, and reaches 2.4 mg as the maximum maintenance dose. Similarly, escalation occurs every 4 weeks.
UK prescribers follow NICE guidance and individual clinical assessment when deciding which kwikpen or auto-injection device suits your circumstances. Both medications require ongoing clinical monitoring and assessment of effectiveness and side effects. Neither is prescribed off-label in standard UK practice—both are used within their licensed indications for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions.
Prescriber assessment includes your current BMI using our free BMI calculator context, medical history, other medications, and previous weight management attempts. Access in the UK is through NHS specialist tier 3 services (with variable regional availability and waiting times) or private online clinical assessment with a UK-licensed prescriber. Either route requires a formal prescription; neither medication is available without professional clinical review.
- 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 is the main difference between Mounjaro and Wegovy mechanism?
Mounjaro is a dual GIP and GLP-1 receptor agonist activating two hormone pathways, whilst Wegovy is a GLP-1 receptor agonist only. This dual action in Mounjaro may contribute to slightly higher average weight loss in clinical trials, but individual suitability depends on your personal health profile, which your prescriber will assess.
Which medication shows better weight loss results in clinical trials?
SURMOUNT trials showed Mounjaro achieved approximately 15–21% average body weight loss, whilst STEP trials showed Wegovy achieved approximately 14.9%. However, these are trial averages. Individual results vary significantly, and both medications are effective for many people. Your prescriber will discuss realistic expectations based on your circumstances.
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 UK conversion chart—any switch requires stopping one medication and starting another with appropriate clinical guidance. Never attempt to switch without professional advice, as dosing and titration schedules differ significantly.
Are Mounjaro and Wegovy available on the NHS in the UK?
Both are licensed and can be prescribed through NHS specialist weight management services (tier 3), though regional availability varies widely and waiting lists can be several months to years. Private online prescribing with a UK-licensed prescriber is also available. Either route requires a full clinical assessment and a valid prescription.
What should I ask my prescriber when comparing these medications?
Ask which medication they believe better suits your health profile, medical conditions, and medications you're taking. Discuss side effect profiles, injection frequency (both are weekly), cost if private, monitoring requirements, and realistic weight loss expectations. Your prescriber will base their recommendation on your individual assessment, not marketing or popularity.
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