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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Not Lost Any Weight On Mounjaro — What This Means
If you've been taking Mounjaro and haven't noticed any weight loss yet, you're not alone — and there are several reasons this might be happening. Weight loss on Mounjaro varies significantly between individuals, and the timeline, dose, and lifestyle factors all play important roles. This guide explains what the clinical evidence shows, when to expect results, and when to speak with your prescriber about adjusting your treatment plan.
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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 May Be Delayed or Absent
Dose too low: Mounjaro requires dose titration over several weeks. You start at 2.5 mg and increase by 2.5 mg every 4 weeks up to your effective dose (often 10–15 mg). If you're still on a starting or low dose, your body may not yet be experiencing the full appetite-suppressing effects. Clinical trials showed significantly higher weight loss at maximum doses (15 mg) compared to lower doses.
Timeline too short: Weight loss with Mounjaro doesn't happen immediately. Most clinical trial participants saw meaningful results between weeks 12–24. If you've been on Mounjaro for fewer than 8–12 weeks, weight loss may still be beginning. The SURMOUNT-1 trial measured results at 72 weeks, not 4–8 weeks.
Calorie intake not reduced: Mounjaro is a weekly weight loss injection that works alongside lifestyle changes, not instead of them. If calorie intake hasn't decreased, weight loss won't occur — even with medication. The medication may reduce appetite, but it doesn't eliminate the need for a calorie deficit.
Plateau or initial plateau: Some people experience rapid early weight loss followed by a plateau. This is normal. Weight loss is not always linear, and plateaus lasting 2–4 weeks are common before further loss resumes.
Clinically BackedWeight Loss
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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.
When to Speak With Your Prescriber
If you've been on Mounjaro for 12+ weeks at a therapeutic dose (10 mg or higher) with no weight loss and you're maintaining a calorie deficit, contact your prescriber. They may:
- Review your dosing schedule and consider escalation to 15 mg (the maximum dose)
- Assess whether Mounjaro is the right medication for you
- Check for underlying medical conditions affecting weight loss (thyroid disorder, PCOS, medication interactions)
- Discuss alternative or additional weight loss strategies
Use our GLP-1 weight loss calculator to track your projected progress at different doses, and monitor your weight consistently using our free progress tracker to identify whether subtle changes are occurring.
- 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.
How long does it take to see weight loss on Mounjaro?
Clinical trials showed meaningful weight loss between weeks 12–24. Most people don't see significant results in the first 4–8 weeks. If you're still on a low dose (2.5–5 mg) or early in treatment, continue as prescribed. Dose escalation happens every 4 weeks, so therapeutic doses (10–15 mg) aren't usually reached until week 12–20.
Does Mounjaro work without diet changes?
No. Mounjaro is designed to work alongside a reduced-calorie diet and increased physical activity. The medication may reduce appetite and help you eat less, but it doesn't create a calorie deficit on its own. Without reducing calorie intake, weight loss won't occur even at higher doses.
Could a medical condition be preventing weight loss?
Yes. Conditions like hypothyroidism, polycystic ovary syndrome (PCOS), Cushing's syndrome, and certain medications can interfere with weight loss. If you've been on Mounjaro 12+ weeks at a high dose with no progress, ask your GP to check your thyroid function and other relevant health markers.
What if I'm not seeing results at 15 mg Mounjaro?
If you've reached the maximum dose (15 mg weekly) and followed a consistent calorie deficit for 12+ weeks with no weight loss, speak with your prescriber. They can assess whether Mounjaro is working for you or discuss alternative medications. Individual response varies — some people respond better to other GLP-1 medications, or may benefit from additional support.
Is Mounjaro the right weight loss injection for me?
Not everyone responds equally to Mounjaro. Your prescriber can help determine if a different medication might work better, or if a mounjaro vs wegovy comparison is relevant for your situation. Factors like your medical history, other medications, and how your body responds to GLP-1 medications all influence effectiveness. A clinical assessment with your prescriber is essential.
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.