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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Weight Plateau on Mounjaro vs Wegovy — What's the Difference?
If you've reached a weight plateau while taking Mounjaro, you're not alone — weight loss naturally slows as your body adapts to treatment. But how does Mounjaro compare to Wegovy when progress stalls? Both are prescription-only weekly weight loss injections approved in the UK, but they work through different mechanisms and may suit different individuals. Understanding the differences can help your prescriber decide whether continuing your current medication or exploring an alternative is right for you.
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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) is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways simultaneously. In the SURMOUNT-1 clinical trial, participants on Mounjaro 15 mg averaged weight loss of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and physical activity.
Wegovy (semaglutide) is a single GLP-1 receptor agonist — activating one pathway. In the STEP-1 trial, participants on Wegovy 2.4 mg achieved average weight loss of approximately 14.9% over 68 weeks under the same lifestyle conditions.
The dual mechanism of Mounjaro may explain why clinical trial participants lost more weight on average. However, individual results vary significantly — some people respond better to one mechanism than another. A prescriber cannot predict your personal response before treatment begins. Using our free GLP-1 weight loss calculator, you can explore estimated outcomes at different dose levels, though actual results depend on your unique metabolism and adherence.
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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.
Reaching a Plateau — Causes and Next Steps
Weight plateaus are a natural part of weight loss. As you lose weight, your body requires fewer calories at rest, and your metabolism adapts. On a prescription weight loss injection like Mounjaro or Wegovy, a plateau may occur because:
- Your body has adapted to the current dose
- You've reached a natural equilibrium point
- Diet or activity levels have drifted
- Medical factors (thyroid, hormones, medications) are influencing weight
Your prescriber may suggest dose escalation, reviewing your diet and exercise, or in some cases, exploring whether switching to a different medication class might be beneficial. Both Mounjaro and Wegovy require ongoing clinical oversight — never adjust doses or switch medications without guidance from your GP or prescriber. Track your progress with our free progress tracker to identify true plateaus versus natural short-term fluctuations.
- 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 does weight loss slow down on Mounjaro?
As you lose weight, your body's calorie requirements decrease, and you naturally adapt to the medication over time. This metabolic adaptation is normal. Your prescriber may increase your dose, review your diet, or discuss alternative approaches. Weight loss isn't linear — short-term plateaus don't mean treatment has stopped working.
Is Mounjaro or Wegovy better for breaking a weight plateau?
There's no single "better" medication — it depends on your individual response. Mounjaro's dual mechanism achieved higher average weight loss in trials, but some people respond better to Wegovy's single GLP-1 pathway. A prescriber assesses your health, previous response, and suitability before recommending any change.
Can I switch from Mounjaro to Wegovy if I hit a plateau?
A prescriber can consider switching between medications, though this is typically done after optimising your current dose and lifestyle factors. The approximate Mounjaro 15 mg equivalent in Wegovy is 2.4 mg, but any switch must be managed by your healthcare provider — don't change medications without clinical guidance.
How long should I wait before concluding I've hit a true plateau?
Weight naturally fluctuates day-to-day due to water retention, hormones, and food timing. A true plateau typically means no significant change over 4–6 weeks. Use our free BMI calculator and progress tracker to monitor trends rather than daily changes — this gives a clearer picture of whether you've genuinely plateaued.
What does the SURMOUNT trial tell us about Mounjaro and weight loss?
SURMOUNT-1 showed participants on Mounjaro 15 mg lost approximately 20.9% of their body weight over 72 weeks alongside a reduced-calorie diet and exercise. However, this is an average — some lost less, some lost more. Individual factors like adherence, diet quality, and baseline metabolism significantly affect outcomes.
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.