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 Injection Offers Better Value?
Both Mounjaro and Wegovy are prescription-only weight management injections available in the UK, but they work differently and may have different costs depending on whether you access them through the NHS or privately. Understanding the clinical differences, trial results, and eligibility criteria can help you and your GP make an informed decision about which medication might be suitable for you. This guide compares both options factually so you can see what the evidence shows about each.
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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, meaning it activates two separate hormone pathways in your body. In the SURMOUNT-1 clinical trial, participants taking 15 mg Mounjaro lost an average of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it targets a single hormone pathway. In the STEP-1 trial, participants on 2.4 mg Wegovy achieved average weight loss of approximately 14.9% body weight at 68 weeks under the same lifestyle conditions.
Both are once-weekly injections. The clinical trial data suggests Mounjaro may produce a greater average weight loss, though individual results vary significantly. A prescriber will assess which mechanism might suit your health profile and medical history. Use our free GLP-1 weight loss calculator to explore projected outcomes at different doses for either medication.
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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
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Cost, Eligibility, and Access in the UK
Private costs for both medications vary by dose and provider, ranging roughly £129–£320 per month. NHS access is through specialist tier 3 weight management services, though availability and waiting times vary significantly by region and ICB. Eligibility for either medication requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes or high blood pressure. Use our free BMI calculator to check your personal BMI, then discuss NHS referral or private options with your GP. Both medications require a clinical assessment before prescription — a prescriber will evaluate your suitability based on your individual health, medications, and medical history.
- 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 cheaper than Wegovy in the UK?
Cost varies by provider and dose. Both typically cost between £129–£320 monthly privately. NHS costs depend on regional availability. A prescriber or pharmacist can advise on current pricing for your specific dose. Neither medication is assured to be significantly cheaper than the other — price comparison depends on your chosen provider and dose level.
Which medication causes fewer side effects — Mounjaro or Wegovy?
Both have similar common side effects: nausea, diarrhoea, constipation, and stomach pain. Individual tolerance varies. Clinical trials show both are generally well-tolerated, with side effects often decreasing over time. Your prescriber will discuss risks and benefits specific to your health during assessment.
Can I switch from Wegovy to Mounjaro if I'm not seeing results?
Any medication switch must be managed by your prescriber. There is no official conversion chart — doses are not directly equivalent. Approximate guidance exists (e.g., Wegovy 2.4 mg ≈ Mounjaro 15 mg), but switching requires a new clinical assessment and prescription. Discuss this with your GP or weight management service.
Will the NHS prescribe Mounjaro or Wegovy as a low-cost option?
NHS prescription is through specialist tier 3 services, not standard GP prescription. Availability is limited and varies by region. Waiting lists can be lengthy in many areas. Private prescription is an alternative but costs apply. Ask your GP about NHS referral options in your area.
Which medication is most suitable for me — Mounjaro or Wegovy?
Suitability depends on your individual health history, medications, BMI, and any weight-related health conditions. A licensed prescriber will assess this during clinical evaluation. Both are effective; neither is universally "better." Your prescriber will recommend based on your personal circumstances, not price alone.
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.