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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Mounjaro for Weight Loss — How It Works in the UK
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection licensed in the UK for adults living with obesity or overweight with health conditions. As a dual GIP and GLP-1 receptor agonist, it works differently from other weight loss medications by activating two natural hormone pathways to help reduce appetite and support feeling fuller after smaller meals. Access through the NHS follows a specific pathway via specialist weight management services, though private prescribing is also available. This guide explains NHS eligibility, how the drug works, and what you need to know about accessing treatment 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.
NHS Eligibility and Specialist Services Access
Mounjaro eligibility through NHS specialist services requires:
- BMI of 30 kg/m² or above, OR
- BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, hypertension, dyslipidaemia, sleep apnoea, or cardiovascular disease)
- For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds apply (BMI 27.5 or above may qualify)
NHS access to this weekly weight loss injection is through tier 3 specialist weight management services, not standard GP prescription. Your GP can refer you to your local service, but waiting lists vary significantly by region. NICE has approved tirzepatide for use within specialist NHS services. In clinical trials, participants lost an average of 15–21% of their body weight alongside reduced-calorie diet and increased physical activity — though individual results vary considerably. Treatment is adjusted over weeks, with doses escalating from 2.5 mg to a maximum of 15 mg weekly.
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 Route for Mounjaro in the UK
NHS route: Free at point of care through tier 3 specialist services, but involves GP referral, specialist assessment, and often significant waiting lists (months to years in some regions). Access depends on your local Integrated Care Board (ICB) availability and capacity.
Private route: Available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber. No NHS referral needed, faster access, but costs approximately £150–£250 monthly depending on dose. Both routes require a clinical assessment to confirm suitability. Our free BMI calculator and GLP-1 weight loss calculator can help you understand your starting point and estimate potential outcomes.
- 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.
Is Mounjaro the same as a slimming injection?
Mounjaro is a specific brand of tirzepatide, a GIP and GLP-1 receptor agonist. "Slimming injection" is a colloquial UK term for prescription weight loss medications. Other weight loss injections include Wegovy (semaglutide) and Saxenda (liraglutide). All require a prescription and clinical assessment.
How long does it take to see results with Mounjaro?
Initial weight loss may appear after 2–4 weeks, but significant results typically emerge after 8–12 weeks of consistent use alongside lifestyle changes. The drug works best with reduced calorie intake and increased physical activity. Individual timelines vary.
What are the main side effects of Mounjaro in the UK?
Very common side effects include nausea, diarrhoea, vomiting, and constipation — usually mild and temporary as your body adjusts. Stomach pain, injection site reactions, and fatigue are also reported. Serious side effects are rare but require urgent medical attention (severe stomach pain, allergic reactions).
Can I get Mounjaro through my GP without specialist referral?
Standard NHS Mounjaro prescription comes through tier 3 specialist weight management services, not routine GP prescription. Your GP can refer you, but the specialist team makes the final decision. Private online prescribers can assess you directly without NHS referral.
How does Mounjaro compare to Wegovy for weight loss?
Both are prescription-only weekly injections licensed in the UK. Mounjaro (tirzepatide) uses dual GIP+GLP-1 activation; Wegovy (semaglutide) uses GLP-1 only. Clinical trials suggest Mounjaro may produce slightly greater average weight loss (~20% vs ~15%), but individual results vary significantly. Your prescriber advises which suits you best.
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.