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
What Results Can You Expect From Mounjaro?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK. Clinical trial data shows it may help adults lose weight alongside a reduced-calorie diet and increased physical activity. However, individual results vary significantly based on lifestyle changes, dose, genetics, and how long you take the medication. This guide explains what clinical evidence shows about Mounjaro outcomes and how realistic expectations support long-term success.
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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.
Clinical Trial Results for Mounjaro
The SURMOUNT-1 clinical trial tracked adults taking Mounjaro for 72 weeks. Results showed average weight loss of approximately 15% of body weight at 5 mg dose, 19.5% at 10 mg dose, and 20.9% at the maximum 15 mg dose. All participants also followed a reduced-calorie diet and increased physical activity. In numerical terms, someone weighing 100 kg might lose around 15–21 kg on average — but this is not assured.
Important context: These are average results. Some people lost significantly more weight, others less. The trial included participants with and without type 2 diabetes. Results were measured at 72 weeks — ongoing weight loss or stabilisation may differ after stopping treatment. The tirzepatide dose was increased gradually over 20 weeks, with participants remaining on each dose for at least 4 weeks before escalation.
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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.
Individual Variation and Real-World Factors
Clinical trial averages do not predict your personal outcome. Weight loss depends on how strictly you follow dietary changes, your baseline weight and metabolism, genetics, age, other medications, and underlying health conditions like PCOS or thyroid disorders. Some people see results within weeks; others take 3–4 months. The Mounjaro KwikPen dose you reach — whether 5 mg, 10 mg, 15 mg, or somewhere in between — also affects results. Your GP or prescriber will assess your individual situation and monitor progress. Use our free BMI calculator to track your starting point, and our GLP-1 weight loss calculator to see projected outcomes at different doses.
- 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.
How much weight did people lose on Mounjaro in clinical trials?
The SURMOUNT-1 trial showed average weight loss of 15–21% of body weight over 72 weeks, depending on the dose used. At the 15 mg maximum dose, the average was approximately clinically studied weight loss. However, individual results ranged widely — some people lost more, others less. These results were achieved alongside reduced-calorie diet and increased physical activity.
Will I get the same results as the clinical trial?
Individual results vary significantly. Clinical trials report averages across hundreds of participants with different starting weights, metabolisms, and adherence levels. Your actual results depend on your lifestyle changes, the dose you take, how long you stay on the medication, your genetics, and other health factors. Your prescriber can give you more personalised guidance based on your circumstances.
How long does it take to see Mounjaro results?
Weight loss typically begins within 2–4 weeks for many people, though some see changes sooner or later. Results are often more noticeable after 8–12 weeks as your dose increases during the titration phase. The first 20 weeks involve gradual dose escalation, so full effects build over time. Patience and consistent lifestyle changes support better outcomes.
How does Mounjaro compare to Wegovy for weight loss?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both GLP-1 medications, but Mounjaro is a dual GIP and GLP-1 agonist, which may offer slightly different effects. Clinical trials suggest Mounjaro produces average weight loss of 15–21%, while Wegovy shows approximately 15%. However, direct comparison is difficult — results depend on individual factors, not just the medication. Your prescriber can advise which is more appropriate for you.
What happens to weight loss results if I stop taking Mounjaro?
Weight loss is not permanent after stopping the medication. Clinical data suggests that without continued lifestyle changes, people gradually regain weight. Some maintain results through sustained diet and exercise; others regain weight over months. Long-term success depends on building lasting habits alongside any medication use. Your GP can discuss whether ongoing treatment or maintenance strategies are appropriate for you.
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.