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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Does Mounjaro Not Work For Some People?
Mounjaro (tirzepatide) is an effective weight loss medication for many UK adults, but it doesn't produce the same results for everyone. Some people experience significant weight loss, whilst others see modest results or no change at all. This guide explains why individual responses vary, who is most likely to benefit, and what alternatives are available through the NHS and private prescribing in the UK.
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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.
Why Mounjaro Results Vary Between Individuals
Clinical trials showed that Mounjaro helps most people lose weight, but individual results vary significantly. In the SURMOUNT-1 trial, some participants lost around 15% of body weight whilst others lost over 20% — at the same dose. This variation depends on several factors:
- Genetics — how your body responds to GLP-1 and GIP hormone pathways differs between individuals
- Metabolism — baseline metabolic rate and insulin sensitivity affect weight loss potential
- Lifestyle adherence — Mounjaro works alongside a reduced-calorie diet and physical activity; results are limited without these changes
- Dose response — some people need higher doses (up to 15mg weekly via the KwikPen) to see meaningful results
- Medical conditions — type 2 diabetes, thyroid disorders, and other conditions may affect response
- Medications — other medicines you take may interact or affect weight loss potential
Your GP or prescriber can assess your individual circumstances and help determine whether dose adjustment or continued use 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
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NHS Eligibility and Prescribing Pathway
In the UK, Mounjaro is available through NHS specialist tier 3 weight management services following NICE approval. Eligibility requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea). NHS access is through referral from your GP, though waiting lists in many regions are lengthy.
If Mounjaro isn't working or you're not eligible for NHS prescribing, your GP may discuss alternatives including Wegovy (semaglutide), Saxenda (liraglutide), or non-pharmacological approaches. Private prescribing is also available following an online clinical assessment, allowing faster access to tirzepatide without NHS referral.
Some people find that Mounjaro becomes less effective over time (weight loss plateaus), or side effects make continuing difficult. In these cases, your prescriber may recommend dose adjustment, a temporary break, or switching to an alternative GLP-1 medication like Wegovy. Calculate your potential weight loss at different doses using our free GLP-1 weight loss calculator to understand realistic expectations for your situation.
Lifestyle factors remain crucial — Mounjaro supports weight loss but does not assures it. Sustainable results come from combining medication with a reduced-calorie diet, increased physical activity, and behaviour change. Check your current BMI with our free BMI calculator to establish a baseline and understand your health context before starting treatment.
- 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 Mounjaro work better for some people than others?
Individual response depends on genetics, baseline metabolism, insulin sensitivity, dose titration, adherence to diet and exercise, and existing medical conditions. Clinical trials show average results, but your personal response may differ significantly. Your prescriber can assess whether dose adjustment or continued use is appropriate for you.
Does not losing weight on Mounjaro mean it's not right for me?
Not necessarily. Some people experience slower initial weight loss or need a higher dose. Mounjaro requires a reduced-calorie diet and physical activity alongside the injection to be effective. If you've been on a stable dose for 12+ weeks with no change, discuss alternatives with your GP or prescriber.
Can I switch from Mounjaro to Wegovy if Mounjaro isn't working?
Yes, switching between GLP-1 medications is possible and may help if one medication isn't producing expected results. Both Mounjaro (tirzepatide) and Wegovy (semaglutide) work on similar pathways but have slightly different mechanisms. Your prescriber will advise on the best approach and timing for switching.
What does the NHS say about Mounjaro if it's not working?
The NHS, via NICE guidance, recommends continuing Mounjaro only if meaningful weight loss (typically 5%+ of body weight) is achieved within 12 weeks. If no progress is made, your specialist should review the prescription. This assessment happens through your tier 3 weight management service.
Are there other weight loss options if Mounjaro doesn't work for me?
Yes. Other NHS-approved options include Wegovy (semaglutide) and Saxenda (liraglutide). Non-medication approaches include tier 3 behaviour change programmes, very low calorie diets under supervision, and bariatric surgery for severe obesity. Your GP can discuss which option suits your circumstances.
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.