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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I've Stopped Losing Weight on Mounjaro — What This Means
Weight loss plateaus are common when taking Mounjaro, and there are several reasons why this happens. If your weight loss has stalled after initial progress, this doesn't necessarily mean Mounjaro isn't working — it often reflects how your body responds to the medication over time. Understanding the difference between Mounjaro and alternative options like Wegovy, and knowing when to speak to your prescriber, can help you decide next steps. This guide explains what causes weight loss stalls and how the two main prescription weight loss injections compare.
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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.
How Mounjaro and Wegovy Work Differently
Mounjaro and Wegovy use different mechanisms, which may explain varying weight loss patterns. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways, whereas Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. Clinical trial data showed Mounjaro helped participants lose an average of 15–21% of body weight over 72 weeks (SURMOUNT-1), while Wegovy showed average weight loss of approximately 15% over 68 weeks (STEP-1). This difference in mechanism may affect how your body responds to the weekly weight loss injection over time. Individual results vary significantly, and some people respond better to one medication than the other. Dose titration also matters — Mounjaro reaches a maximum of 15 mg weekly, while Wegovy's maximum is 2.4 mg. Your prescriber may adjust your dose if weight loss slows.
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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 Weight Loss Can Slow or Stop
Weight loss plateaus happen because your body adapts to medication, dietary changes, and physical activity. Metabolic adaptation — where your body burns fewer calories as it becomes lighter — is a normal biological response. Additionally, as you lose weight, you require fewer calories to maintain your lower body weight, meaning your calorie deficit naturally reduces. Some people also find that side effects like nausea and vomiting reduce over time, leading to increased appetite. Your prescriber can explore options: dose escalation (if you're not at maximum), switching medications, adjusting diet, or increasing physical activity. Use our free BMI calculator and GLP-1 weight loss calculator to track your progress and share data with your GP or prescriber — this helps inform decisions about next steps.
- 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 did I lose weight quickly at first on Mounjaro but then stop?
Initial weight loss often includes water loss and reduced food intake as side effects (nausea) are strongest. As your body adapts and side effects ease, weight loss typically slows. This is normal. Metabolic adaptation also occurs — your body burns fewer calories at a lower weight. Discuss with your prescriber whether dose escalation or other adjustments might help restart progress.
Should I switch from Mounjaro to Wegovy if weight loss stops?
Switching medications is a decision for your prescriber based on your individual response. Some people respond better to one medication than the other due to different mechanisms (Mounjaro's dual GIP+GLP-1 vs Wegovy's GLP-1 only). Before switching, explore whether dose escalation, diet adjustments, or increased activity might help. Your prescriber will assess suitability.
Is it normal for weight loss to slow on a weekly weight loss injection?
Yes. Weight loss typically follows a pattern: rapid initial loss (weeks 1–12), then gradual slowing as your body adapts. This is true for all GLP-1 and GIP/GLP-1 medications. Reaching a plateau doesn't mean the medication has stopped working — it reflects normal physiology. Even modest continued weight loss supports health benefits.
Can I ask my GP to increase my Mounjaro dose if I've stopped losing weight?
Yes, discuss this with your prescriber (GP or specialist). Mounjaro is typically escalated every 4 weeks up to a maximum of 15 mg weekly. If you haven't reached the maximum dose, dose escalation may help. However, your prescriber will consider your individual circumstances, including side effects and health conditions, before recommending changes.
How can I track my weight loss progress accurately?
Use our free progress tracker to log weight consistently (same day/time each week). Record measurements in both kg and stone — this UK weight converter approach helps spot trends. Also track non-scale progress: energy levels, how clothes fit, and fitness improvements. Share this data with your prescriber during reviews to inform decisions about medication adjustments or lifestyle changes.
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.