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: What to Expect at Your Consultation
If you're considering prescription weight loss treatment in the UK, your GP or a licensed prescriber will need to assess whether Mounjaro or Wegovy is right for you. Both are prescription-only GLP-1 (or GIP/GLP-1) receptor agonist injections approved for weight management, but they work differently and have different dosing schedules. This guide explains the key differences so you understand what to discuss at your consultation and which factors your prescriber will consider.
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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.
How Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in the body. The GIP pathway helps regulate fat storage and utilisation, while the GLP-1 pathway reduces appetite. Clinical trials (SURMOUNT-1) showed an average weight loss of approximately 15–21% of body weight over 72 weeks, depending on dose.
Wegovy (semaglutide) is a GLP-1-only receptor agonist, activating just the GLP-1 appetite-regulation pathway. The STEP-1 clinical trial showed an average weight loss of approximately 14.9% of body weight over 68 weeks on the maximum dose of 2.4 mg.
- Mounjaro uses a once-weekly injection (doses 2.5–15 mg)
- Wegovy uses a once-weekly injection (doses 0.25–2.4 mg)
- Both require 4 weeks minimum at each dose before increasing
- Individual results vary significantly — clinical trial averages don't predict personal 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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Suitability: What Your Prescriber Will Consider
At your consultation, your GP or licensed prescriber will assess which medication may be more appropriate based on your personal health history, not just weight. Both medications require a UK prescription and clinical assessment — they're not available over-the-counter. Your prescriber will review your eligibility (BMI ≥30, or ≥27 with weight-related health conditions), any other medications you take, and whether you have conditions affecting medication absorption, such as gastroparesis.
You can use our free GLP-1 weight loss calculator to explore projected outcomes at different doses, and our BMI calculator to understand your current health category. However, your prescriber's assessment is the deciding factor in which medication is right for you — there is no universally "better" option between the two.
- 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 between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist, activating two appetite and metabolism pathways. Wegovy (semaglutide) activates GLP-1 only. Both are once-weekly injections approved for UK weight management. Clinical trials showed similar average weight loss (15–21% for Mounjaro, 14.9% for Wegovy), but individual results vary.
How long does a Mounjaro or Wegovy consultation take in the UK?
Initial consultations typically take 20–30 minutes. Your prescriber will assess your medical history, current medications, BMI, and any weight-related health conditions. You'll also discuss side effects, injection technique, and realistic expectations. Follow-up consultations are usually shorter, focusing on dose tolerance and progress.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, switching is possible, but it must be managed by your prescriber. There is no official established conversion chart — approximate equivalences are based on clinical practice. Your prescriber will advise on timing and whether to restart at a lower dose or continue from your current level. Never switch without medical guidance.
Do I need to see my GP before getting a Mounjaro or Wegovy prescription?
Not necessarily. NHS access requires a GP referral to a specialist tier 3 weight management service. Private access is through an online consultation with a UK-licensed prescriber — no GP referral needed. Either way, a clinical assessment is mandatory before any prescription is issued.
What happens if neither Mounjaro nor Wegovy is suitable for me?
If neither medication is appropriate, your prescriber may suggest other approaches: lifestyle interventions (diet and exercise support), alternative weight loss medications like Saxenda (liraglutide), or referral to NHS tier 3/4 services for comprehensive weight management support, which may include bariatric surgery assessment.
Ready to take control of your weight loss journey?
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