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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Monjaro vs Wegovy — Cost and Effectiveness Compared
Looking for the best value weight loss injection in the UK? Both Monjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weekly injections approved for adults with excess weight or weight-related health conditions. While neither medication assures specific discounts, their costs, mechanisms, and effectiveness differ significantly. Understanding these differences helps you have an informed conversation with your prescriber about which might suit your situation best. Both require a clinical assessment before prescription.
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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.
Clinical Evidence and Mechanism Differences
Monjaro and Wegovy work differently despite both being weight loss injections. Monjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways to help reduce appetite and regulate food intake. Wegovy (semaglutide) is a GLP-1 receptor agonist only — it targets a single pathway. In clinical trials, Monjaro showed average weight loss of approximately 15–21% of body weight at the maximum 15mg dose (SURMOUNT trial data), whilst Wegovy showed approximately clinically studied weight loss at the maximum 2.4mg dose (STEP trials). Both are used alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly — some people respond better to one medication than the other. Your prescriber will consider your health profile, medical history, and personal circumstances when deciding which is appropriate for you.
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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.
UK Pricing, Access, and Individual Suitability
Neither Monjaro nor Wegovy are typically discounted through the NHS, though both are available on specialist NHS weight management services in some regions — however, NHS access often involves lengthy waiting lists. Private costs range from approximately £129–£320 per month depending on dose and provider. Monjaro starts at a lower dose (2.5mg) and escalates gradually, whilst Wegovy starts at 0.25mg. Costs may appear lower initially but scale with dose increases. The "best value" injection depends on your individual response, not the brand name. Use our free GLP-1 weight loss calculator to estimate potential outcomes, and discuss pricing transparently with any prescriber or pharmacy. Your GP can also refer you to specialist NHS services if eligible.
- 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 Monjaro cheaper than Wegovy in the UK?
Neither medication has official discounts, and pricing varies by dose and provider. Both typically cost £129–£320 per month privately. Monjaro starts lower but scales with dose increases. NHS access is free but availability is limited and waiting lists are long in many regions. Compare providers and doses directly.
Which injectable is more effective — Monjaro or Wegovy?
Clinical trials show both support significant weight loss — Monjaro averaged 15–clinically studied weight loss, Wegovy around 15%. Individual results vary substantially. Effectiveness depends on how your body responds, not which is "better". Your prescriber will assess which suits your health profile.
Can I switch from Wegovy to Monjaro?
Yes, but only under prescriber guidance. There is no official conversion chart — approximate equivalence exists (e.g. Wegovy 2.4mg ≈ Monjaro 10mg), but any switch must be managed by your prescriber with a minimum 72 hours between doses.
How long does Monjaro or Wegovy take to work?
Both typically show noticeable appetite reduction within 1–2 weeks, but meaningful weight loss usually emerges over 4–8 weeks as you maintain a calorie deficit. Consistent use alongside dietary changes and physical activity is essential for results.
Do I need a prescription for either injectable in the UK?
Yes, both Monjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only medicines in the UK. You'll need a clinical assessment from a GP or licensed prescriber to confirm eligibility before either can be prescribed to you.
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.