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 Actually Work for Weight Loss?
Yes, Mounjaro (tirzepatide) has been shown to work for weight loss in clinical trials and is now approved by NICE for use within NHS specialist weight management services across the UK. However, "working" means it may help you lose weight alongside diet and exercise changes — not that results are assured or the same for everyone. This guide explains what the evidence actually shows, how it works, and what you can realistically expect from this dual GIP and GLP-1 receptor agonist injection.
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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.
What Does the Clinical Evidence Show?
The SURMOUNT-1 clinical trial, which led to Mounjaro's approval for weight management, followed over 500 adults for 72 weeks. On average, participants taking the maximum 15 mg dose lost approximately 20.9% of their body weight — roughly 22 kg for someone starting at 105 kg. Those on the 10 mg dose lost about 19.5%, and those on 5 mg lost around 15%. Importantly, these results were achieved alongside a reduced-calorie diet and increased physical activity — medication alone did not produce these outcomes.
- Results varied significantly between individuals — some lost much more, others less
- Participants who discontinued the medication typically regained weight over time
- The medication appears to work best when combined with lifestyle changes
- Benefits include improved blood sugar control and cardiovascular markers, not just weight loss
NICE approved tirzepatide (Mounjaro) in March 2024 for NHS use, recognising it as an effective option for specialist tier 3 weight management services in the UK.
Clinically BackedWeight Loss
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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.
How Mounjaro Works and NHS Access
Mounjaro works differently from older weight loss injections like Wegovy because it activates two hormone pathways — GIP and GLP-1 — rather than just one. This dual action may explain why some people achieve stronger results. The Mounjaro KwikPen is injected once weekly, starting at 2.5 mg and gradually increasing to a maximum of 15 mg over several months (dose titration).
On the NHS in the UK, Mounjaro is available through specialist tier 3 weight management services, typically accessed by GP referral. Access varies by region, and waiting lists can be lengthy. If you have a BMI of 30 or above, or 27–29.9 with weight-related conditions like type 2 diabetes, prediabetes, or hypertension, you may be eligible. Our GLP-1 weight loss calculator can help you estimate potential weight loss outcomes at different doses, and our BMI calculator shows whether you might meet NHS eligibility thresholds.
Mounjaro works differently from older weight loss injections like Wegovy because it activates two hormone pathways — GIP and GLP-1 — rather than just one. This dual action may explain why some people achieve stronger results. The Mounjaro KwikPen is injected once weekly, starting at 2.5 mg and gradually increasing to a maximum of 15 mg over several months (dose titration).
On the NHS in the UK, Mounjaro is available through specialist tier 3 weight management services, typically accessed by GP referral. Access varies by region, and waiting lists can be lengthy. If you have a BMI of 30 or above, or 27–29.9 with weight-related conditions like type 2 diabetes, prediabetes, or hypertension, you may be eligible. Our GLP-1 weight loss calculator can help you estimate potential weight loss outcomes at different doses, and our BMI calculator shows whether you might meet NHS eligibility thresholds.
- 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 everyone?
No. Clinical trials show Mounjaro helps most people lose weight, but results vary significantly. Some lose 25%+ of body weight, others lose 10%. Success depends on your starting weight, adherence to diet and exercise changes, genetics, and individual response. Stopping the medication typically leads to weight regain over time.
Is Mounjaro approved by NICE and NHS in the UK?
Yes. NICE approved tirzepatide (Mounjaro) in March 2024 for use within NHS specialist weight management services. It's available through tier 3 services for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Regional availability varies, and waiting lists can be several months.
How does Mounjaro compare to Wegovy for weight loss?
Mounjaro (dual GIP+GLP-1) showed slightly higher average weight loss (~21%) than Wegovy (single GLP-1, ~15%) in clinical trials. However, these are averages — individual results vary greatly. The choice between them depends on your clinical assessment, NHS availability, and individual factors. Your GP or prescriber can advise which suits you.
What happens if I stop taking Mounjaro?
Weight typically returns over time. Mounjaro works while you're taking it by affecting appetite and metabolism. Once you stop, these effects gradually wear off. This is why sustainable results depend on maintaining the lifestyle changes (diet and exercise) you've built while on the medication.
How long does it take to see results with Mounjaro?
Most people begin noticing reduced appetite within the first 1–2 weeks. Measurable weight loss usually appears after 4–8 weeks. The full effect takes several months as doses are gradually increased (titration). Your GP or prescriber will monitor progress and adjust doses accordingly.
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.