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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Using Mounjaro to lose weight in the UK
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection now available in the UK through NHS specialist services and private prescribing. It works as a dual GIP and GLP-1 receptor agonist, helping to regulate appetite and support feeling fuller after smaller meals. In clinical trials, people using Mounjaro lost an average of 15–21% of their body weight alongside reduced-calorie diet and increased physical activity. This NHS and UK health guide explains how Mounjaro works, who is eligible, and how to access it in the UK.
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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 NICE guidance for Mounjaro weight loss
NICE approval: Mounjaro (tirzepatide) has been approved by NICE for use within NHS specialist weight management services for eligible adults.
Eligibility criteria: You may be eligible for prescription weight loss treatment, including Mounjaro, if you have:
- A BMI of 30 kg/m² or above, OR
- A BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, or sleep apnoea)
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher cardiovascular risk at lower weights. Access to Mounjaro through the NHS is typically via tier 3 specialist weight management services, usually following a GP referral. Waiting times vary significantly across UK regions. Our free GLP-1 weight loss calculator can help you explore projected outcomes at different Mounjaro doses if you're considering treatment.
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.
NHS vs private access to Mounjaro in the UK
NHS route: Referral from your GP to a tier 3 or tier 4 specialist weight management service. Assessment, prescription, and monitoring through the NHS. Available free but subject to regional waiting lists and service availability. Some areas have limited or no specialist services.
Private route: Online consultation with a UK-licensed prescriber, followed by prescription from a GPhC-registered pharmacy. Available without NHS referral. Faster access. Costs typically £129–£320+ per month depending on dose. Use our BMI calculator to check your eligibility status before exploring options with a 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.
How much weight can I expect to lose with Mounjaro on the NHS?
Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks when used alongside diet and exercise changes. Individual results vary significantly based on dose, adherence, diet, and physical activity. Your prescriber will discuss realistic outcomes for your situation.
What is the difference between Mounjaro and Wegovy for NHS weight loss?
Both are GLP-1 based weight loss injections available in the UK. Mounjaro is a dual GIP and GLP-1 agonist (up to 15mg weekly). Wegovy is a GLP-1 agonist only (up to 2.4mg weekly). Clinical trials suggest Mounjaro may produce slightly greater average weight loss. Both require prescription and clinical assessment.
How long does it take to see weight loss results with Mounjaro?
Most people begin to notice appetite reduction within the first few doses. Measurable weight loss typically appears within 4–8 weeks. The full effect is usually seen around 16–20 weeks. Results continue to improve with continued use. Consistency with diet and exercise is essential.
Can I get Mounjaro on the NHS if I have a BMI of 27?
Yes, if your BMI is 27–29.9 and you have at least one weight-related health condition (such as type 2 diabetes, prediabetes, high blood pressure, sleep apnoea, or cardiovascular disease). If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, a BMI of 27.5 or above may qualify. Ask your GP about referral to specialist services.
What are the most common side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, constipation, and stomach pain—especially during dose escalation. These typically reduce over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and allergic reactions. Always report any concerning symptoms to your prescriber immediately.
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.