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
Does Mounjaro Always Work for Weight Loss?
Mounjaro (tirzepatide) is not a one-size-fits-all solution for weight loss. While clinical trials showed impressive average results, individual outcomes vary significantly. Some people experience substantial weight loss, while others may have a more modest response. Your results depend on genetics, lifestyle changes, dose, and how your body responds to the medication. Understanding what Mounjaro can and cannot assures is essential before seeking a UK prescription through NHS or private routes.
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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 Effective Is Mounjaro — What the Evidence Shows
The SURMOUNT-1 clinical trial demonstrated that Mounjaro may help participants lose an average of 15–21% of their body weight over 72 weeks, depending on dose and when measured. However, these are average results — individual weight loss varies widely. Some participants lost significantly more; others lost less. A dual GIP and GLP-1 receptor agonist, Mounjaro works by reducing appetite, increasing fullness after meals, and slowing gastric emptying, but your body's response to these mechanisms is unique.
- At 5 mg dose: average ~clinically studied weight loss
- At 10 mg dose: average ~clinically studied weight loss
- At 15 mg (maximum) dose: average ~clinically studied weight loss
- All results achieved alongside a reduced-calorie diet and increased physical activity
- Success rates are higher when combined with lifestyle changes — medication alone is not enough
Your GP or prescriber can discuss realistic expectations for your individual situation. Use our free GLP-1 weight loss calculator above to explore potential outcomes at different doses, though your actual results may differ.
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.
Why Mounjaro Doesn't Work for Everyone
Several factors determine whether Mounjaro will be effective for you personally. Genetics play a major role — some people's bodies are naturally more responsive to GLP-1 and GIP signalling. Adherence matters significantly: missing doses, not following the reduced-calorie diet, or not increasing physical activity reduces effectiveness. Underlying medical conditions, certain medications, and metabolism variations also influence results. Additionally, some people experience side effects (nausea, diarrhoea, constipation) that limit how well they tolerate higher doses, potentially reducing weight loss. If you're considering Mounjaro via NHS tier 3 services or private prescription, your prescriber will assess whether this medication is suitable for your health profile and likely response.
- 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.
Does Mounjaro always result in significant weight loss?
No. While clinical trials showed average weight loss of 15–21%, individual results vary considerably. Some people lose substantial weight; others experience modest loss. Success depends on genetics, lifestyle changes, dose tolerance, and how your body responds to the medication. Your GP can discuss realistic expectations for you.
Can I get Mounjaro on the NHS in the UK?
Mounjaro is available through NHS specialist tier 3 weight management services for eligible adults. You need a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. Access varies significantly by region. Waiting lists can be lengthy, and not all areas offer it yet. Your GP can advise on availability in your area.
What makes Mounjaro different from Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whereas Wegovy (semaglutide) is a GLP-1 agonist only. This dual mechanism may contribute to Mounjaro's higher average weight loss in trials. Both are prescription-only injectables taken once weekly. Clinical results show Mounjaro achieved slightly greater average weight loss in its trials, but individual response varies.
What if Mounjaro doesn't work for me?
If you don't see adequate weight loss after several months on Mounjaro (typically assessed at 12–16 weeks), your prescriber may increase your dose, switch you to another medication like Wegovy, or discuss whether the medication is suitable for you. Weight management is not solely medication-based — diet, activity, and behaviour change are equally important for success.
How long does it take to see results from Mounjaro?
Most people begin noticing changes in appetite and portion sizes within 2–4 weeks of starting or increasing their dose. Measurable weight loss typically becomes apparent after 4–8 weeks. The full effect of each dose usually takes 4 weeks to develop, which is why prescribers wait at least 4 weeks before increasing. Patience and consistent lifestyle changes alongside the medication are key.
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.