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 Really Work?
Yes, clinical evidence shows Mounjaro (tirzepatide) does help with weight loss in most people — but results vary significantly. In the SURMOUNT-1 trial, participants on the maximum 15 mg dose lost an average of around 21% of their body weight over 72 weeks, compared to around 3% with placebo. However, these results were achieved alongside a reduced-calorie diet and increased physical activity. Mounjaro is a prescription-only medicine, so a clinical assessment by a licensed prescriber is required before you can use it. This guide explains how the evidence translates to real-world weight loss and what "really works" actually means.
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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 the Clinical Trial Evidence Works
The evidence that Mounjaro works comes primarily from the SURMOUNT-1 clinical trial, which tested tirzepatide in over 2,600 adults with overweight or obesity across 69 clinical sites globally. Participants were randomly assigned to receive tirzepatide at different doses (5 mg, 10 mg, or 15 mg) or a placebo injection, alongside a reduced-calorie diet (500 kcal/day deficit) and lifestyle coaching. After 72 weeks:
- 5 mg tirzepatide: ~15% average body weight loss
- 10 mg tirzepatide: ~19.5% average body weight loss
- 15 mg tirzepatide: ~20.9% average body weight loss
- Placebo group: ~3% average body weight loss
This shows tirzepatide does produce significantly greater weight loss than placebo. The dose titration process (starting at 2.5 mg and increasing weekly over several months) allows your body to adjust, reducing side effects. To understand your own healthy weight range, try our free BMI calculator to see where you currently sit on the NHS guidelines.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Important Context: Individual Results Vary
Clinical trial averages do not predict individual outcomes. Some people lose significantly more weight, others less — genetics, metabolism, adherence to lifestyle changes, and how your body responds to the GLP-1 and GIP pathways all matter. Weight loss is not assured. Mounjaro also works differently from Wegovy (semaglutide, a GLP-1-only medication) — tirzepatide activates two hormone pathways instead of one, which may explain slightly higher average weight loss in trials, though both are effective for many people. In the UK, Mounjaro is available on the NHS through specialist tier 3 weight management services (access varies by region and waiting lists can be long) or privately following an online clinical assessment. Your prescriber will assess whether Mounjaro is suitable for your specific health profile, BMI, and any existing medical conditions.
- 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 work for everyone?
No. Mounjaro helps most people lose weight, but not everyone responds equally. Some people are "non-responders" or respond less effectively. A reduced-calorie diet and increased physical activity alongside the injection are essential — Mounjaro is not effective on its own. Your individual metabolism, genetics, and adherence to lifestyle changes all affect how well it works for you.
How long does it take to see results with Mounjaro?
Most people notice appetite reduction within the first 1–2 weeks of starting, but measurable weight loss typically appears after 4–8 weeks. Maximum weight loss usually takes 12–16 weeks as your dose increases. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses based on current evidence.
Is Mounjaro better than Wegovy?
Mounjaro and Wegovy (semaglutide) are both effective. Clinical trials suggest Mounjaro may produce slightly higher average weight loss because it targets two hormone pathways (GIP and GLP-1) rather than one. However, both medications work well for many people. The "best" medication depends on individual factors — your prescriber can advise which suits you.
What happens if you stop taking Mounjaro?
Weight typically returns over time after stopping. Mounjaro is not a permanent supports — it's a tool to support weight loss alongside diet and exercise. Some people continue long-term, others use it to establish new habits then transition to lifestyle-only management. Your GP or prescriber can discuss the right approach for you.
Can I get Mounjaro on the NHS in the UK?
Yes, but availability is limited. Mounjaro is available through NHS specialist tier 3 weight management services — not standard GP prescription. Waiting lists and regional availability vary significantly. Private prescription through a UK-licensed online service is faster but involves a cost. Either route requires a clinical assessment confirming you're eligible.
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.