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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Mounjaro Plateau vs Wegovy — What's the Difference?
When taking tirzepatide (Mounjaro) or semaglutide (Wegovy) for weight management, some people experience a plateau where weight loss slows or stops, even while remaining on medication. Both are prescription-only GLP-1 receptor agonists licensed in the UK, but they work differently — Mounjaro is a dual GIP and GLP-1 agonist, whilst Wegovy activates GLP-1 alone. This guide compares how these medications approach weight loss plateaus and helps you understand which may be more suitable for your individual health needs.
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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.
Trial Data and Mechanism Differences
Mounjaro (tirzepatide) activates two hormone pathways — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. In the SURMOUNT-1 clinical trial, participants taking tirzepatide 15 mg achieved an average weight loss of approximately 20.9% of body weight over 72 weeks. Wegovy (semaglutide) activates GLP-1 only. In the STEP-1 trial, participants on semaglutide 2.4 mg achieved an average weight loss of approximately 14.9% of body weight over 68 weeks.
The dual mechanism in Mounjaro may theoretically offer advantages in initial weight loss phase. However, both medications can cause weight loss plateaus as the body adapts. Individual response varies significantly — some people achieve sustained loss on either medication, whilst others experience plateaus regardless of which tirzepatide or semaglutide dose they're taking.
- Mounjaro: dual GIP + GLP-1 mechanism, doses 2.5–15 mg once weekly
- Wegovy: GLP-1 mechanism only, doses 0.25–2.4 mg once weekly
- Both require dose titration over 16–20 weeks to reach full dose
- Both show similar plateau patterns in long-term follow-up studies
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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.
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Suitability and Prescriber Assessment
Whether Mounjaro or Wegovy is more suitable for you depends on individual factors including your medical history, concurrent medications, response to dose escalation, and prescriber preference. Neither medication is universally "better" — clinical trial averages mask significant individual variation. Some people respond well to one but not the other; others experience similar outcomes on both.
If you experience a weight loss plateau on either medication, your prescriber may: continue the current dose (plateaus can be temporary), consider dose escalation if not yet at maximum, review diet and activity levels, or discuss switching to the alternative medication. Use our free GLP-1 weight loss calculator to understand projected outcomes at different doses, and the BMI calculator to track progress objectively alongside your prescriber's guidance.
- Individual results vary — trial averages don't predict personal outcomes
- Plateau management requires prescriber input, not self-adjustment
- Both medications are prescription-only and require clinical assessment
- 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.
Can you switch from Mounjaro to Wegovy if you hit a plateau?
Switching between medications is possible but requires prescriber guidance. There is no official conversion chart — your prescriber will assess your individual response and may recommend continuing, escalating dose, or switching based on your health. Any medication change must be managed through a licensed prescriber.
Why do weight loss plateaus happen on Mounjaro or Wegovy?
Plateaus occur because your body adapts to the medication over time. Appetite suppression may reduce, metabolic adaptation occurs, and weight loss naturally slows as you lose weight. This is normal physiology, not medication failure. Plateaus can be temporary, and resuming loss is possible with continued treatment.
Does Mounjaro work better than Wegovy for breaking through plateaus?
Trial data shows Mounjaro achieves slightly higher average weight loss (20.9% vs 14.9%), but individual results vary widely. Some people plateau on Mounjaro and respond well to Wegovy, and vice versa. No medication "breaks through" all plateaus — prescriber guidance and lifestyle factors matter more than which medication you take.
How long does a weight loss plateau typically last on these injections?
Plateaus vary in duration — some last weeks, others months. Continuing treatment whilst maintaining diet and activity, and working with your prescriber, often leads to resumed loss. Temporary plateaus are normal and don't indicate the medication has stopped working.
What should I do if I plateau on a weight loss injection?
Speak to your prescriber before making any changes. They may review your diet, increase activity, check medication adherence, or consider dose adjustment. Never self-adjust medication. Our progress tracker helps you log consistent data to share with your prescriber for informed decision-making.
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.