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
Free tracker included with every download this week
Not Losing Weight on Mounjaro — When to Consider Alternatives
If you're not losing weight on Mounjaro, you're not alone — individual responses to GLP-1 and GIP/GLP-1 medications vary significantly. Some people experience gradual weight management, whilst others lose weight slowly or plateau. This doesn't mean Mounjaro isn't working; it may mean your dose needs adjusting, your lifestyle factors need review, or a different medication like Wegovy might suit you better. Understanding the differences between these weekly weight loss injections can help you and your prescriber make the right decision.
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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.
Mounjaro vs Wegovy — Mechanism and Trial Data Differences
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both prescription weight loss injections licensed in the UK, but they work differently. Mounjaro is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways simultaneously. Wegovy is a GLP-1 only receptor agonist — it targets one pathway. Clinical trial data shows differences: the SURMOUNT-1 trial found Mounjaro users lost an average of 15–20.9% body weight depending on dose, whilst the STEP-1 trial showed Wegovy users lost approximately 14.9% body weight. However, these are population averages — individual results vary considerably. Some users respond better to Mounjaro's dual mechanism, whilst others achieve better results with Wegovy's single GLP-1 pathway. Your prescriber will consider your personal response when deciding if a switch is appropriate.
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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 Plateau and What to Try
Weight loss plateaus are common on any GLP-1 medication — your body may adapt over time, or your dose may not be optimal yet. Before assuming Mounjaro isn't working, check: Are you on your maximum tolerated dose? (Mounjaro goes up to 15 mg weekly). Have you had 4+ weeks on your current dose? (dose escalation takes time). Are you eating in a calorie deficit alongside the injection? GLP-1 medications support appetite reduction, but don't replace the need for dietary changes. Use our free GLP-1 weight loss calculator to review realistic projections for your dose. If you've been on a stable maximum dose for 12+ weeks with no weight loss and no appetite reduction, discuss switching to Wegovy or reviewing your overall plan with your prescriber.
- 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 I switch from Mounjaro to Wegovy if I'm not losing weight?
Yes, switching between GLP-1 medications is possible and managed by your prescriber. There is no official conversion chart, but approximate equivalences exist (15mg Mounjaro ≈ 2.4mg Wegovy). Your prescriber will assess whether a switch is appropriate based on your response, dose history, and side effects. The switch requires a new prescription.
How long should I give Mounjaro before deciding it's not working?
You should be on your maximum tolerated dose for at least 12 weeks before concluding Mounjaro isn't effective. Dose escalation takes 4 weeks per step, and weight loss momentum can vary. If you haven't reached 15mg yet, ask your prescriber about continuing escalation. Document your weight weekly using our free progress tracker to identify trends rather than daily fluctuations.
Is Wegovy more effective than Mounjaro for weight loss?
Not necessarily. Mounjaro showed slightly higher average weight loss in SURMOUNT trials (15–20.9% vs 14.9% for Wegovy), but individual responses vary. Some people respond better to Wegovy's single GLP-1 mechanism, others to Mounjaro's dual action. Effectiveness depends on your personal biology, lifestyle adherence, and dose tolerance — not on which is theoretically "better."
What else affects weight loss on Mounjaro besides the injection?
Diet, physical activity, sleep, stress, and underlying health conditions all influence weight loss. Mounjaro reduces appetite, but you must maintain a calorie deficit through food choices. Poor sleep and high stress can impair weight loss. Review your GP if you have undiagnosed thyroid problems, PCOS, or diabetes — these require separate management alongside GLP-1 medication.
Can my prescriber adjust my Mounjaro dose if it's not working?
Yes. If you've not reached 15mg, your prescriber may continue the escalation schedule. If you're at 15mg with no weight loss, they may discuss switching medications, reviewing your diet, checking for medication interactions, or investigating underlying health factors. Some people need longer on maximum dose before seeing results — patience is important.
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.