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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Why Mounjaro Isn't Working For You — And How Wegovy Compares
If you're taking Mounjaro and not seeing the weight loss results you expected, you're not alone — medication response varies significantly between individuals. This guide explains why Mounjaro may not be delivering results for you, how it differs from the alternative GLP-1 medication Wegovy, and what options your prescriber might discuss. Both are prescription-only medicines that work differently, and suitability depends on your individual health profile and response to treatment.
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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.
Clinical Trial Data and Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in the body. In the SURMOUNT-1 clinical trial, participants taking the 15mg dose (maximum) lost an average of 20.9% of their body weight over 72 weeks.
Wegovy (semaglutide) is a GLP-1-only receptor agonist — it activates a single hormone pathway. In the STEP-1 trial, participants on the 2.4mg dose (maximum) lost an average of 14.9% of body weight over 68 weeks.
However, these are trial averages alongside reduced-calorie diet and increased physical activity. Individual results vary considerably — some people respond excellently to one medication and poorly to another. The dual mechanism of Mounjaro doesn't assures better results for every person. Your prescriber may suggest switching to Wegovy if Mounjaro hasn't produced expected weight loss after adequate time at therapeutic dose (typically 12–16 weeks at maximum tolerated dose).
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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 Individual Response Varies and What to Discuss with Your Prescriber
Weight loss medication response depends on genetics, baseline metabolism, gut hormone sensitivity, adherence to lifestyle changes, and other medications you're taking. Just because Mounjaro works for others doesn't mean it will work for you at the same rate — and that's medically normal.
Before assuming Mounjaro "isn't working", check you've reached your therapeutic dose (typically 10–15mg) and sustained it for at least 12 weeks. Common reasons for disappointing results include: staying at lower doses due to side effects, insufficient calorie deficit despite the medication, or individual variation in receptor sensitivity.
If Mounjaro truly isn't delivering results after adequate time and dose, your GP or prescriber can discuss alternatives. Switching to Wegovy is a reasonable next step — the single GLP-1 mechanism works better for some individuals. Both require clinical assessment before switching.
- 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 long should I give Mounjaro before deciding it's not working?
Most prescribers recommend at least 12–16 weeks at your therapeutic dose (usually 10–15mg) before evaluating effectiveness. Weight loss may be slower initially. If you're still at lower doses due to side effects, you haven't yet reached the dose used in clinical trials. Discuss timing with your GP or prescriber.
Is Wegovy definitely better than Mounjaro if Mounjaro didn't work for me?
No — Wegovy works better for some individuals and worse for others. Trial averages show slightly lower weight loss with Wegovy (14.9% vs 20.9%), but individual results vary. Some people respond excellently to Wegovy despite poor Mounjaro response, and vice versa. Your prescriber will assess suitability individually.
What's the main difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates two hormone pathways — GIP and GLP-1 — while Wegovy (semaglutide) activates only the GLP-1 pathway. This dual mechanism is why Mounjaro showed higher average weight loss in trials, but it doesn't work better for everyone. Individual body chemistry determines which works best for you.
Can I use the GLP-1 weight loss calculator to compare results between medications?
Our free GLP-1 weight loss calculator can show projected weight loss ranges at different doses of both Mounjaro and Wegovy based on trial data. However, this is an estimate only — your personal results depend on your unique health profile, lifestyle changes, and medication response.
What should I do if neither Mounjaro nor Wegovy work for me?
If both GLP-1 medications underperform, discuss other options with your GP or specialist weight management service. These might include: other weight loss medications (such as liraglutide/Saxenda), referral to NHS specialist tier 3 services, or evaluation for bariatric surgery if severe obesity with significant comorbidities is present.
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.