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
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Not Losing Weight on Mounjaro — What to Know
If you're on Mounjaro but not seeing the weight loss results you expected, you're not alone. Weight loss on prescription weight loss injections varies significantly between individuals, and several factors can affect your progress. This guide explains why weight loss may plateau on Mounjaro, how it compares to Wegovy, and what steps you can take. Always discuss any concerns with your prescriber, as they can assess your individual situation and adjust your treatment if needed.
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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.
Mounjaro vs Wegovy — Mechanism and Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways to support appetite regulation. Wegovy (semaglutide) is a GLP-1 agonist only, activating a single hormone pathway. Clinical trial data shows different average outcomes: in the SURMOUNT-1 trial, Mounjaro at 15 mg resulted in average weight loss of approximately 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy at 2.4 mg (maximum dose) achieved average weight loss of approximately 14.9% over 68 weeks. However, individual results vary considerably — some people lose more, some less, and some experience plateaus. The difference in mechanism (dual vs single) may explain why some individuals respond better to one weekly weight loss injection than the other, but this can only be determined through individual trial and clinical assessment with your prescriber.
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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.
Why Weight Loss May Plateau on Mounjaro
Weight loss plateaus are common and do not mean the medication has stopped working. Several factors can affect progress: insufficient calorie deficit despite reduced appetite, inadequate physical activity, underlying medical conditions (thyroid, insulin resistance), certain medications that interact with Mounjaro, or simply that your body has reached a natural equilibrium. Some people respond better to higher doses — your prescriber may adjust your mounjaro dose titration to optimise results. Using our free GLP-1 weight loss calculator can help you understand projected outcomes at different doses. If you've been on the same dose for 8+ weeks without progress, discuss dose escalation or a potential switch to an alternative weekly weight loss injection with your prescriber.
- 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.
Why am I not losing weight on Mounjaro if clinical trials showed significant results?
Clinical trial results show averages — individual responses vary widely. Some people achieve 20%+ weight loss, others 5-10%, and some experience plateaus. Weight loss depends on your calorie intake, activity level, baseline metabolism, underlying health conditions, and how your body responds to the medication. Your prescriber can help assess whether your current dose is optimal.
Is Wegovy better than Mounjaro for weight loss?
Clinical trials show Wegovy achieved approximately 14.9% average weight loss, while Mounjaro achieved 20.9% on average — but individual results vary considerably. Some people respond better to Mounjaro's dual mechanism, others to Wegovy's single GLP-1 mechanism. Your prescriber will recommend based on your personal health profile and suitability, not on trial averages alone.
How long should I stay on Mounjaro before considering a switch to Wegovy?
This is a prescriber decision. Typically, you should be on your target Mounjaro dose (usually 15 mg) for at least 8-12 weeks before considering a switch. Your GP or prescriber will assess whether switching is appropriate based on your progress, side effects, and overall health. Switching between medications requires medical guidance.
Can I use the BMI calculator to track progress on Mounjaro?
Yes — our free BMI calculator helps you track how your BMI changes alongside your weight. Regular BMI monitoring can help you see progress beyond just the scale, especially if you're gaining muscle while losing fat. Log your measurements regularly using our progress tracker to visualise trends over time.
What should I discuss with my prescriber if I'm not losing weight on Mounjaro?
Discuss your current dose, how long you've been at that dose, your calorie intake and activity level, any new medications, underlying health conditions (thyroid, PCOS, diabetes), and whether you're experiencing appetite suppression. Your prescriber may recommend dose escalation, lifestyle adjustments, or exploring alternative medications like Wegovy — this requires a uk prescription weight loss assessment.
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.