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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Montjaro in the UK: A Complete Health Guide
Montjaro (tirzepatide) is a prescription-only weight management injection now available in the UK for adults who qualify. This guide explains how Montjaro works, UK eligibility criteria, NHS access, and what you need to know before considering this treatment. Whether you're exploring options through the NHS or private prescribing, understanding the facts helps you make informed decisions about your health. Use our free BMI calculator above to check your current BMI and see where you stand against NHS healthy weight guidelines.
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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.
How Montjaro Works and UK Eligibility
Montjaro is a dual GIP and GLP-1 receptor agonist — this dual mechanism sets it apart from other weight loss injections available in the UK. It activates two natural hormone pathways that help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. In clinical trials, participants using Montjaro lost an average of 15–21% of their body weight alongside a reduced-calorie diet and increased physical activity — though individual results vary significantly.
UK eligibility for Montjaro:
- 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, high blood pressure, abnormal cholesterol, sleep apnoea, or cardiovascular disease)
- For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds may apply due to higher health risks at lower weights
- Must be at least 18 years old and not pregnant or breastfeeding
A prescriber will assess your individual health status before issuing a prescription.
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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.
Montjaro Access in the UK: NHS and Private Routes
In the UK, Montjaro access is available through two routes. NHS access is through tier 3 specialist weight management services following GP referral, though availability and waiting times vary significantly by region and local commissioning. Private access is through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber — this route does not require NHS referral and can be faster, though costs typically range from £129–£320 monthly depending on dose. Whichever route you choose, a qualified prescriber will assess whether Montjaro is appropriate for your health needs. Try our GLP-1 weight loss calculator to estimate potential outcomes at different doses.
- 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 is the difference between Montjaro and Wegovy?
Montjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. This dual mechanism means Montjaro may work differently for different people. Clinical trials showed Montjaro achieved slightly higher average weight loss (15–21% vs approximately 15%), but individual results vary. Both are prescription-only and require clinical assessment.
Can I get Montjaro on the NHS in the UK?
Montjaro is available on the NHS through specialist tier 3 weight management services, but access varies significantly by region. You would need referral from your GP and assessment by a specialist team. Many areas have long waiting lists. Private online prescribing offers faster access but involves costs. Contact your GP to discuss options in your area.
What are the common side effects of Montjaro?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — particularly when starting or increasing doses. These often improve over time as your body adjusts. Seek urgent medical attention for severe stomach pain (possible pancreatitis), allergic reactions, or gallbladder problems. Always discuss side effects with your prescriber.
How much weight will I lose on Montjaro?
Clinical trials showed average weight loss of 15–21% of body weight at 72 weeks — but individual results vary significantly. Some people lose more, others less. Weight loss depends on your starting weight, adherence to a reduced-calorie diet, physical activity level, and individual factors. Use our weight loss calculator to estimate potential outcomes based on clinical data.
Do I need a prescription to get Montjaro in the UK?
Yes, Montjaro is prescription-only in the UK. You cannot buy it without a valid prescription from a UK-licensed prescriber. This prescription can come from NHS specialist services or through a private online assessment with a GPhC-registered provider. The prescriber assesses your eligibility and suitability based on your health history.
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.