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- 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, and Clinical Comparison
If you're considering prescription weight loss medication in the UK, you've likely come across both Mounjaro and Wegovy. Both are injectable GLP-1 medications, but they differ in mechanism, dosing, trial outcomes, and cost. This guide compares them factually to help you understand the key differences—though your GP or prescriber will assess which, if either, is suitable for your individual situation. Both medications require a prescription and clinical assessment before dispensing.
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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 Outcomes
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways rather than one. In the SURMOUNT-1 clinical trial, participants on the maximum 15 mg dose 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 single GLP-1 receptor agonist. In the STEP-1 clinical trial, participants on the maximum 2.4 mg dose lost approximately 14.9% of their body weight over 68 weeks under similar lifestyle conditions.
Important context: these are trial averages, individual results vary significantly, and both medications require lifestyle changes to work effectively. Neither assures weight loss. Use our GLP-1 weight loss calculator to explore projected outcomes at different doses.
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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.
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Cost Comparison and UK Availability
On the private market in the UK, Mounjaro typically costs between £150–£320 per month depending on dose and provider, whilst Wegovy ranges from approximately £130–£300 per month. Costs vary between GPhC-registered online pharmacies, so it's worth comparing. On the NHS, both medications are available through specialist tier 3 weight management services, though regional availability and waiting times vary considerably. Access depends on your BMI, weight-related health conditions, and your local integrated care board (ICB) commissioning.
Regardless of route (NHS or private), both require a prescription from a UK-licensed prescriber following clinical assessment. Neither is available to purchase without a prescription.
Dosing schedules differ: Mounjaro begins at 2.5 mg and escalates every 4 weeks to a maximum of 15 mg, all once-weekly. Wegovy starts at 0.25 mg and escalates over 16 weeks to a maximum of 2.4 mg, also once-weekly. The different titration schedules mean different timelines to reach full dose. Calculate your current BMI using our free BMI calculator to understand your eligibility baseline, though your prescriber will make the final assessment based on your full health profile.
- 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?
Private costs are similar—typically £150–£320 for Mounjaro and £130–£300 for Wegovy monthly, depending on dose and provider. Prices vary between pharmacies, so compare before purchasing. On the NHS, cost is not a patient consideration; both are provided through specialist weight management services where available.
Which caused more weight loss in clinical trials?
In clinical trials, Mounjaro (20.9% average loss) showed numerically higher weight loss than Wegovy (14.9% average loss). However, these are trial averages with different populations and timelines. Individual results vary considerably, and clinical trial outcomes may not reflect real-world results.
What's the difference between GLP-1 and GIP+GLP-1?
GLP-1 (Wegovy) activates one hormone pathway controlling appetite and blood sugar. Mounjaro's dual GIP+GLP-1 mechanism activates two pathways, which may explain different average weight loss outcomes. Both work differently in different people—your prescriber will assess which mechanism may suit you.
Can I switch between Mounjaro and Wegovy?
Switching between medications is possible but must be managed by your prescriber. There is no official conversion chart between doses. Any switch requires clinical assessment and guidance on timing and new dosing. Never switch without consulting your healthcare provider.
Which is more likely to be available on the NHS?
Both are approved by NICE for NHS specialist weight management services. Availability depends on your regional ICB and local commissioning decisions. Waiting times and access criteria vary significantly across the UK. Contact your local tier 3 weight management service to check local eligibility and availability.
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