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 You May Stop Losing Weight on Mounjaro
Weight loss plateaus are common during Mounjaro treatment, even when taken as prescribed. A temporary slowdown in weight loss — or no loss for a few weeks — doesn't mean the medication isn't working. Your body may be adjusting, or you may have reached a natural stabilisation point. Understanding why this happens, and what your NHS or private prescriber can do about it, helps you make informed decisions about your treatment. We'll explain the science, practical steps, and your options in the UK healthcare system.
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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.
Why Weight Loss Slows or Stops on Mounjaro
Weight loss on Mounjaro typically follows a pattern: faster initial loss, then gradual slowing. Several factors explain this:
- Adaptation: Your body adjusts to the medication over time, meaning the appetite-suppressing effect may feel less pronounced as weeks pass. This is normal, not a failure of the drug.
- Dose stabilisation: If you're still on a lower maintenance dose (e.g. 5 mg or 7.5 mg), your prescriber may recommend escalating to a higher dose if clinically appropriate. The SURMOUNT clinical trial showed greater average weight loss at 10 mg and 15 mg doses than at 5 mg.
- Reaching a natural set point: Your body may stabilise at a weight where the medication's effects are balanced with your current calorie intake and activity level.
- Lifestyle drift: Small increases in portion sizes, reduced physical activity, or dietary changes can offset the medication's appetite-suppressing effects — even if the change feels minor.
- Metabolic adaptation: As you lose weight, your metabolic rate adjusts slightly downward, meaning you burn fewer calories at rest.
A weight loss plateau lasting 2–4 weeks is common and rarely a cause for concern, particularly if you're still in the dose titration phase.
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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.
What to Do If Weight Loss Stops on Mounjaro — NHS and Private Routes
First steps: Keep a food diary for 2–3 weeks to check for hidden calorie increases. Ensure you're still in a moderate calorie deficit alongside your Mounjaro. Track your progress using our free progress tracker to spot patterns you might miss. Increase physical activity if possible — aim for at least 150 minutes of moderate activity per week, as NHS guidelines recommend.
If a plateau persists beyond 4 weeks: Contact your prescriber. Through NHS tier 3 specialist services, your clinician may recommend escalating your dose if you're not at 15 mg (the maximum weekly injection dose). Private prescribers can similarly adjust your dose based on response and safety. Your prescriber will also review any medications that might slow weight loss, such as certain antidepressants.
- 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.
Is it normal to stop losing weight while taking Mounjaro?
Yes, plateaus are common. Weight loss speed naturally slows as you lose more weight — this is called metabolic adaptation. It's particularly normal after 3–6 months on a stable dose. Most plateaus lasting 2–4 weeks resolve with continued adherence. However, if no weight loss occurs for 8+ weeks, discuss dose escalation or other factors with your prescriber.
Will my prescriber increase my Mounjaro dose if I stop losing weight?
Possibly. If you're on a dose below 15 mg and a plateau lasts beyond 4 weeks, your NHS specialist or private prescriber may recommend escalation. Each dose increase must be separated by at least 4 weeks. However, dose increases aren't automatic — your prescriber will assess your individual situation, including side effects and overall health.
Can I do anything myself to restart weight loss on Mounjaro?
Yes. Check your diet hasn't drifted (portions, snacks, drinks). Ensure a calorie deficit of around 500 kcal daily for steady loss. Increase or vary physical activity — try strength training alongside cardio. Review our GLP-1 weight loss calculator to see projected outcomes at your current dose and lifestyle. Sleep quality and stress also affect weight loss — prioritise both.
How long should I wait before contacting my prescriber about a weight loss plateau?
A 2–4 week plateau is normal and usually temporary. Wait 4 weeks before contacting your prescriber, unless you have other concerns. If no weight change occurs for 8+ consecutive weeks, contact them promptly. They'll review your dose, medication adherence, diet, and activity level to identify next steps.
Does Mounjaro stop working, or do I just get used to it?
Mounjaro doesn't "stop working" — your body adapts to its presence, which is different. The medication continues to affect appetite and fullness signals, but the subjective feeling of reduced hunger may become less noticeable. Dose escalation or dietary review usually restarts weight loss. Studies show sustained benefit at higher doses and with continued adherence over 2+ years. ```
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.