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
Free tracker included with every download this week
Is Wegovy Better Than Mounjaro? A UK Health Perspective
Neither Wegovy nor Mounjaro is universally "better" — suitability depends entirely on individual health, NHS or private access, and prescriber assessment. Both are UK-licensed prescription-only weight management injections with different mechanisms. Wegovy (semaglutide) activates a single GLP-1 pathway, whilst Mounjaro (tirzepatide) works as a dual GIP and GLP-1 receptor agonist. This guide compares their NHS eligibility, clinical trial results, and UK prescribing context to help you understand how each medication differs. Use our GLP-1 weight loss calculator to explore potential outcomes at different doses, and check your BMI using our free BMI calculator to see whether you might meet eligibility criteria.
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Calculate Your BMI Instantly
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 Wegovy and Mounjaro Compare in UK Clinical Practice
Mechanism of action is the fundamental difference. Wegovy activates the GLP-1 receptor only — the same pathway used by Saxenda (liraglutide). Mounjaro, by contrast, activates both GIP and GLP-1 receptors, which is why it's classified as a dual agonist. In the STEP trial, Wegovy achieved average weight loss of approximately 14.9% of body weight at the maximum 2.4 mg dose. In the SURMOUNT-1 trial, Mounjaro achieved approximately 20.9% at the maximum 15 mg dose. However, these trials used different populations and methodologies — direct comparison suggests Mounjaro may produce slightly greater average weight loss, though individual results vary significantly.
- Wegovy: GLP-1 agonist, 0.25–2.4 mg once weekly, average ~clinically studied weight loss
- Mounjaro: GIP+GLP-1 agonist, 2.5–15 mg once weekly, average ~clinically studied weight loss
- Results are from clinical trials — outcomes depend on dose, adherence, and lifestyle changes
Both require sustained reduced-calorie diet and physical activity to be effective. NHS NICE guidance approves both for specialist tier 3 weight management services, though availability varies significantly by region.
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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.
NHS Eligibility and UK Prescribing Access for Both Medications
On the NHS, both Wegovy and Mounjaro are prescribable through tier 3 specialist weight management services following NICE approval. Eligibility is the same for both: BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions (type 2 diabetes, hypertension, cardiovascular disease, or sleep apnoea). For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds may apply. Access via NHS is limited by regional availability and waiting lists — some areas have multi-month delays. Privately, both are available through GPhC-registered online pharmacies following remote clinical assessment, typically costing £129–£320 monthly depending on dose. Your GP can advise on NHS tier 3 referral; private access does not require NHS involvement. The NHS route may be free at point of use, but private routes offer faster access without referral delays.
- 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 more effective than Wegovy?
Clinical trial data suggests Mounjaro may produce slightly greater average weight loss (~21% vs ~15%), but trials used different methodologies. Individual results vary considerably and depend on dose, adherence, diet, and exercise. "More effective" differs for each person — prescriber assessment determines which is more suitable for you.
Can I switch from Wegovy to Mounjaro on the NHS?
Potentially yes, if your tier 3 specialist service approves. No official conversion exists — any switch must be managed by your prescriber. Mounjaro's tirzepatide dose cannot be calculated directly from semaglutide doses. Switching requires clinical reassessment and a new prescription.
Which injection has fewer side effects, Wegovy or Mounjaro?
Both cause similar side effects: nausea, diarrhoea, constipation, and stomach pain. Some patients tolerate one better than the other due to individual variation. Neither is "lower side effect" — your prescriber monitors tolerance and adjusts dose accordingly.
How long does it take to see results with Wegovy or Mounjaro?
Weight loss typically begins within 4–6 weeks of starting treatment, but is gradual. Most weight loss occurs between weeks 8–16. Maximum dose is reached around week 17 for Wegovy, week 21 for Mounjaro. Full results are usually evident by 12–16 weeks of consistent use alongside diet and exercise changes.
Can I get Wegovy or Mounjaro without an NHS referral?
Yes — both are available privately through GPhC-registered online pharmacies without NHS referral. Private access requires a remote clinical assessment with a UK-licensed prescriber. You'll be assessed for eligibility, contraindications, and suitability before a prescription is issued. Private routes do not require waiting for NHS tier 3 services.
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.