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 Work For Everyone?
No — Mounjaro doesn't work the same way for everyone. While clinical trials show that tirzepatide (Mounjaro) can help many adults lose weight, individual results vary significantly. Some people achieve substantial weight loss, others see modest results, and a small percentage may not respond well to the medication. In the UK, Mounjaro is prescribed through NHS specialist services or private providers following a clinical assessment, and whether it's right for you depends on your personal health circumstances, medical history, and individual physiology.
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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.
NHS Eligibility and Individual Response Variation
In the UK, Mounjaro is prescribed through NHS tier 3 specialist weight management services or privately via a UK-licensed prescriber. To be eligible, you typically need a BMI of 30 kg/m² or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. However, meeting eligibility criteria doesn't assures the medication will work for you.
The SURMOUNT clinical trials showed that on average, participants using tirzepatide at the maximum 15 mg dose lost approximately 20.9% of their body weight over 72 weeks — but this masks significant individual variation. Some participants lost over 30% of their body weight, while others lost less than 10%. Age, baseline weight, genetics, metabolism, adherence to diet and exercise, and gut health all influence how well Mounjaro works. Your GP or specialist prescriber can assess your individual circumstances and discuss realistic expectations.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 Results Vary and What Affects Response
Key factors affecting Mounjaro response:
- Dose titration — the 4-week escalation schedule from 2.5 mg to 15 mg allows your body to adjust, but some people respond well at lower doses (5–10 mg) and don't need the maximum
- Lifestyle adherence — Mounjaro works alongside reduced-calorie diet and increased physical activity; without these, results are diminished
- Gastrointestinal side effects — nausea, diarrhoea, and constipation can affect how well you tolerate the medication and stick to dietary changes
- Underlying health conditions — people with type 2 diabetes, PCOS, or other metabolic conditions may respond differently than those without
- Genetics — your family history and individual metabolism partly determine how your body responds to GLP-1 and GIP receptor activation
Use our free GLP-1 weight loss calculator to see projected outcomes based on clinical trial data, but remember your actual results may differ.
- 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.
What percentage of people does Mounjaro work for in the UK?
Mounjaro is effective for most people who use it as prescribed, but "effective" varies. In clinical trials, the majority (80%+) experienced some weight loss, but the amount differed widely. Very few people on Mounjaro experienced no weight loss at all. Your NHS specialist or private prescriber can discuss what "success" means for your health goals.
Can my GP prescribe Mounjaro directly, or does it have to go through NHS tier 3?
In the UK, Mounjaro for weight management is primarily available through NHS tier 3 specialist weight management services (referral needed) or through private online prescribing services. Standard GP practices typically cannot prescribe it for weight management on the NHS, though this varies by region. A private prescriber can assess you without NHS referral.
How do I know if Mounjaro will work for me before starting?
There's no test to predict individual response before starting. Your prescriber will assess your medical history, BMI, any weight-related conditions, and metabolic health. They'll discuss realistic expectations based on clinical trial data and your circumstances. Starting at the lowest dose (2.5 mg) allows monitoring of both effectiveness and side effect tolerance.
What if Mounjaro doesn't work well for me — can I switch to Wegovy instead?
Yes, if Mounjaro isn't suitable or effective for you, a prescriber can discuss switching to Wegovy (semaglutide), which is a single GLP-1 agonist rather than a dual GIP/GLP-1 agonist. Some people respond better to one mechanism than the other. Any switch must be managed by your prescriber with a washout period between medications.
Does starting on a lower Mounjaro dose mean it won't work as well?
Not necessarily. The 4-week dose escalation (2.5 mg → 5 mg → 7.5 mg and beyond) is for tolerability, not effectiveness. Many people achieve good weight loss at 5–10 mg and may not need the maximum 15 mg dose. Your prescriber will adjust based on your response and side effects over the 16–20 week titration period.
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.