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
Does Mounjaro Work for Weight Loss?
Yes, clinical evidence shows Mounjaro can support weight loss in UK adults, but results vary significantly between individuals. Based on the SURMOUNT clinical trials, Mounjaro (tirzepatide) helped participants lose an average of 15–21% of their body weight over 72 weeks alongside reduced-calorie diet and increased physical activity. However, whether it will work for you depends on several factors including your individual health, how your body responds, and whether you can maintain the lifestyle changes that go alongside it. This guide compares Mounjaro with Wegovy (semaglutide) to help you understand how these weekly weight loss injections differ and what the evidence actually shows.
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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 Clinical Evidence Shows Mounjaro Works
Mounjaro's weight loss effect comes from its unique dual mechanism: it activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) hormone pathways. This differs from Wegovy, which is a GLP-1 only receptor agonist. In the SURMOUNT-1 trial, participants taking 15 mg Mounjaro lost approximately 20.9% of body weight on average, compared to Wegovy's STEP-1 trial which showed approximately 14.9% average weight loss on 2.4 mg semaglutide. However, these are averages — individual results range from modest loss to significant reductions.
- SURMOUNT data: 5 mg dose ~15% loss, 10 mg ~19.5% loss, 15 mg ~20.9% loss (72 weeks)
- Mechanism: Dual GIP+GLP-1 vs Wegovy's single GLP-1 mechanism may explain slightly higher average weight loss
- Individual variation: Some people lose 5–10%, others 25%+ — prescriber assessment determines suitability
- Dosing: Mounjaro requires dose titration over 20+ weeks, starting at 2.5 mg and escalating weekly to maximum 15 mg
Both medications are prescription-only and require a clinical assessment before prescription. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses based on trial data.
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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.
Which Is Better — Mounjaro or Wegovy?
Neither is objectively "better" — suitability depends on your individual health, preferences, and prescriber recommendation. Mounjaro may be preferred if you want potentially higher average weight loss and can tolerate weekly injections with dose escalation. Wegovy may suit you if you prefer a simpler dose progression (0.25 mg to 2.4 mg) or if your prescriber recommends it based on your medical history. Both are UK prescription-only medicines requiring assessment through NHS specialist services or private online prescribing. Cost varies — private prices typically range £129–£320 monthly depending on dose. Track your progress using our free progress tracker once prescribed, and use the BMI calculator to monitor your health metrics alongside weight loss.
- 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.
Does Mounjaro actually work for weight loss?
Yes. Clinical trials show Mounjaro helped participants lose 15–21% of body weight on average over 72 weeks, though individual results vary significantly. It works by activating GIP and GLP-1 hormone pathways, reducing appetite and supporting feeling fuller after meals. Results are best alongside reduced-calorie diet and increased physical activity. Your prescriber will assess whether it's suitable for you.
Is Mounjaro better than Wegovy for weight loss?
Clinical trial data suggests Mounjaro produces slightly higher average weight loss (20.9% vs 14.9%), but this reflects average outcomes only. Individual results vary considerably with both medications. Wegovy may suit some people better depending on preferences, tolerability, and prescriber recommendation. Neither is objectively superior — choice depends on personal factors assessed during clinical evaluation.
How much weight can you lose with Mounjaro?
Based on SURMOUNT trials, average weight loss ranged from approximately 15% (5 mg dose) to 20.9% (15 mg dose) over 72 weeks. However, some people lose less, some lose more. Weight loss depends on starting weight, individual metabolism, dose reached, diet adherence, and activity level. Your prescriber can discuss realistic expectations during clinical assessment.
How long does Mounjaro take to work for weight loss?
Weight loss typically becomes noticeable after 4–8 weeks as your dose escalates. Most significant loss occurs weeks 8–20 as you reach therapeutic doses. The SURMOUNT trials measured results at 72 weeks. You must continue the injection weekly — weight often returns if treatment stops — alongside permanent lifestyle changes.
Can I get Mounjaro on the NHS for weight loss?
Yes, NICE has approved tirzepatide (Mounjaro) for NHS use, but access is through tier 3 specialist weight management services following GP referral. Availability varies significantly by region and waiting lists can be lengthy. Private prescription is available through UK-licensed prescribers via online clinical assessment without NHS referral.
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.