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 Is More Affordable in the UK?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections available in the UK, but they work differently and have different costs. If you're looking for affordable weight loss medication, understanding the differences between these two options is essential. This guide compares their mechanisms, clinical trial results, doses, and typical UK pricing so you can make an informed decision with your prescriber.
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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
The key difference between these two medications is their mechanism of action. Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in the body. Wegovy is a GLP-1 receptor agonist only, activating a single pathway. This dual action in Mounjaro may contribute to slightly higher average weight loss in clinical trials. According to SURMOUNT-1 trial data, Mounjaro at the maximum 15 mg dose produced average weight loss of approximately 20.9% of body weight over 72 weeks. The STEP-1 trial showed Wegovy at 2.4 mg produced average weight loss of approximately 14.9% of body weight over 68 weeks. Both medications work by reducing appetite, increasing feelings of fullness, and slowing gastric emptying. Individual results vary significantly, and both require a reduced-calorie diet and increased physical activity alongside the 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.
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Cost, Doses, and Suitability — What Matters Most
Private prescription costs in the UK typically range from £129–£320 per month depending on the dose and pharmacy. Mounjaro requires 4 weeks to escalate between doses (2.5 mg starter through to 15 mg maximum), while Wegovy escalates over 16 weeks (0.25 mg to 2.4 mg). This means reaching full therapeutic dose takes longer with Wegovy, which may affect initial costs. NHS access is available through specialist tier 3 weight management services, but availability varies significantly by region and waiting times can be lengthy. Your GP or prescriber will assess which medication is more suitable based on your individual health, BMI, and any weight-related conditions. Neither medication assures specific weight loss — both work best alongside lifestyle changes.
- 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.
Why is Mounjaro sometimes cheaper than Wegovy?
Pricing varies between pharmacies and doses. At lower doses, Mounjaro is not necessarily cheaper—cost depends on your specific dose, the pharmacy's pricing, and current supply. Always compare prices across GPhC-registered pharmacies. Neither medication is "cheap" overall, but private options are more accessible than waiting for NHS services.
Which medication causes more side effects?
Both have similar common side effects: nausea, diarrhoea, vomiting, and constipation. Individual tolerance varies. Mounjaro's slightly higher average efficacy doesn't mean more side effects—some people tolerate one better than the other. Your prescriber will discuss risks specific to your health.
Can I switch from Wegovy to Mounjaro if Wegovy isn't working?
Potentially, yes—but any switch must be managed by your prescriber. Approximate dose equivalences exist (0.5 mg Wegovy ≈ 5 mg Mounjaro), but there is no official conversion chart. Your prescriber will assess the best transition approach based on your response.
How do I check my personal weight loss potential?
Use our free GLP-1 weight loss calculator to see projected outcomes at different doses. Results are estimates only—actual weight loss depends on your adherence to diet, exercise, genetics, and individual response. Your GP or prescriber can give personalised advice.
Is NHS or private cheaper for weight loss medication?
NHS is free at point of use, but waiting lists for specialist weight management services can be 12+ months in many regions. Private prescription costs £129–£320 monthly but offers quicker access. Compare both routes with your GP to see what's available locally.
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.