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 — Cost, Mechanism & Eligibility in the UK
If you're looking to buy Mounjaro affordably in the UK, it's important to understand how it compares to Wegovy—the other main GLP-1 injection licensed for weight management. Both are prescription-only medications available through NHS specialist services or private online prescribing, but they work differently, cost differently, and may suit different individuals. This guide explains the key differences to help you have an informed conversation with your prescriber or GP.
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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 Trial Data and Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural 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 reduced-calorie diet and increased physical activity. Wegovy (semaglutide) is a GLP-1 receptor agonist only—it activates one pathway. The STEP-1 trial showed average weight loss of around 14.9% of body weight at the maximum 2.4 mg dose over 68 weeks under similar conditions.
The dual mechanism of Mounjaro may offer slightly greater average weight loss in trials, but individual results vary significantly. Both medications slow gastric emptying and reduce appetite. Wegovy requires daily dosing (up to 2.4 mg once weekly), while Mounjaro escalates from 2.5 mg to a maximum of 15 mg once weekly. Neither medication assures specific weight loss outcomes—results depend on diet, activity, genetics, and individual metabolism.
Use our GLP-1 weight loss calculator to see projected weight loss at different doses based on clinical trial data, though your actual results may differ.
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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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Private Cost, NHS Access, and Prescriber Assessment
Private prescriptions for both Mounjaro and Wegovy in the UK typically cost £129–£320 per month depending on dose and provider. Mounjaro's higher starting dose (2.5 mg) means first prescriptions may cost slightly less initially, but the maximum dose (15 mg) is pricier than Wegovy's top dose (2.4 mg). NHS access is available through tier 3 specialist weight management services, though availability and waiting times vary significantly by region (ICB). Your GP can refer you to specialist services if you meet eligibility criteria (BMI ≥30, or ≥27 with weight-related health conditions). A licensed prescriber will assess which medication is appropriate for you based on your health, medical history, and individual factors—not just price. Check your BMI instantly using our free BMI calculator to understand your eligibility.
- 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.
Which is cheaper to buy—Mounjaro or Wegovy?
Private UK prices are similar (£129–£320/month) and vary by provider and dose. Mounjaro's lower starting dose may cost slightly less initially, but maximum doses are comparable. Shop around between GPhC-registered pharmacies. NHS access through specialist services is free but availability varies by region.
Which causes fewer side effects—Mounjaro or Wegovy?
Both cause similar common side effects: nausea, diarrhoea, vomiting, constipation, and abdominal pain. Individual tolerance varies. Your prescriber will monitor for side effects and adjust your dose if needed. Always report serious symptoms (severe stomach pain, changes in vision) immediately.
Is Mounjaro stronger than Wegovy?
Mounjaro's dual GIP+GLP-1 mechanism showed slightly higher average weight loss in trials (15–21% vs 14.9%), but this is not universal. Individual results vary greatly. "Stronger" depends on how your body responds, not the drug mechanism alone. Your prescriber will choose based on your suitability, not potency.
Can I switch from Wegovy to Mounjaro?
Approximate dose equivalences exist (0.5 mg Wegovy ≈ 5 mg Mounjaro), but any switch must be managed by your prescriber. Do not stop one and start the other without guidance. A prescriber will assess whether switching is appropriate and manage the transition safely.
Will the NHS prescribe Mounjaro instead of Wegovy?
NHS tier 3 services may prescribe either, depending on clinical assessment and availability. NICE approved tirzepatide (Mounjaro) for NHS use, but access varies by region and individual factors. Your GP can refer you to specialist services for assessment—the prescriber will recommend the appropriate medication.
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.