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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What to Do If Mounjaro 7.5mg Isn't Working
If you're on Mounjaro 7.5mg and not seeing the weight loss results you expected, you're not alone — individual response to GLP-1 and GIP/GLP-1 medications varies significantly. Before considering alternatives like Wegovy, it's important to understand whether your dose needs adjustment, whether you're giving the medication enough time to work, or whether a different medication might be more suitable for your body. Your prescriber can help assess this. This guide compares Mounjaro and Wegovy to help you have an informed conversation with your GP or prescriber.
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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.
Mounjaro vs Wegovy: Mechanism and Trial Data
Mounjaro (tirzepatide) works via a dual mechanism — it activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptor pathways. In the SURMOUNT-1 clinical trial, participants on the 7.5mg dose lost an average of 19.5% of body weight over 72 weeks, though individual results varied considerably.
Wegovy (semaglutide) activates only the GLP-1 pathway. The STEP-1 trial showed average weight loss of approximately 14.9% of body weight at the maximum 2.4mg dose over 68 weeks.
The dual mechanism is why Mounjaro may theoretically offer stronger appetite suppression, but "stronger" does not mean "effective for everyone." Some people respond better to single-pathway GLP-1 therapy. Individual suitability depends on your unique metabolism, medical history, and how your body responds to each medication.
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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.
When Mounjaro Might Not Be Working — and Your Options
Before switching medications, consider: (1) Dose timing — each dose requires a minimum of 4 weeks to take full effect; (2) Diet and activity — GLP-1 medications work alongside reduced-calorie intake and physical activity, not instead of them; (3) Timeframe — some people take 8–12 weeks to see meaningful results; (4) Individual response — not everyone loses weight on every medication, regardless of mechanism.
If you've been on 7.5mg Mounjaro for at least 12 weeks with consistent lifestyle changes and haven't seen results, discuss with your prescriber whether escalating to 10mg, switching to Wegovy, or exploring other options makes sense for your situation. Your prescriber will assess your individual health context — no two people respond identically.
- 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.
Should I switch from Mounjaro 7.5mg to Wegovy if Mounjaro isn't working?
Not necessarily. Discuss with your prescriber first. Possible steps include: escalating your Mounjaro dose (you may not have reached your optimal dose yet), ensuring you're in a calorie deficit with consistent activity, or waiting longer (some people need 12+ weeks). Only after these are optimised should you consider switching. Switching between tirzepatide and semaglutide requires medical guidance.
What's the difference between Mounjaro's dual mechanism and Wegovy's single GLP-1 mechanism?
Mounjaro activates both GIP and GLP-1 pathways, which may enhance appetite suppression. Wegovy activates GLP-1 only. In trials, Mounjaro showed slightly higher average weight loss (19.5% vs 14.9%), but individual response varies dramatically. Some people respond better to Wegovy despite Mounjaro's dual action — metabolism is individual.
How long should I stay on Mounjaro 7.5mg before deciding it's "not working"?
At least 8–12 weeks at the same dose, provided you're maintaining a calorie deficit and regular physical activity. Each dose requires a minimum of 4 weeks to exert full effect. If you've been consistent with diet and exercise for 12+ weeks without results, that's when to have a prescriber discussion about escalation or alternatives.
Could my lifestyle be the reason Mounjaro 7.5mg isn't working?
Yes — this is very common. GLP-1 and tirzepatide medications reduce appetite and support feeling fuller, but they don't override calorie intake entirely. If you're not in a calorie deficit, or if you've increased activity less than needed, weight loss will stall. Use our free BMI calculator and GLP-1 weight loss calculator to review expected results alongside your actual intake and activity.
Is Mounjaro stronger than Wegovy, so should I expect better results?
Mounjaro's dual mechanism showed higher average weight loss in trials, but "average" is key — individual results vary enormously. Some people lose more on Wegovy than on Mounjaro. Metabolism, genetics, underlying health conditions, and lifestyle adherence matter more than the mechanism. Your prescriber will help determine which is most suitable for you based on your personal health profile.
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.