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 in the UK — What You Need to Know
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight with related health conditions. This UK health guide explains how Mounjaro works, who may be eligible, what to expect from treatment, and how to access it through the NHS or private providers. Understanding this medication can help you make informed decisions about weight management options available to you.
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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 Mounjaro Works and UK Eligibility
Mounjaro is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways in the body to help regulate appetite and support weight management. Unlike single-action medications, this dual mechanism may help reduce food cravings, increase feelings of fullness, and support more sustainable weight loss when used alongside a reduced-calorie diet and increased physical activity.
In the UK, Mounjaro may be prescribed for adults with:
- A BMI of 30 kg/m² or above (obesity), OR
- A BMI of 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or cardiovascular disease
For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply, recognising that these groups face higher health risks at lower weight levels. Your GP or a licensed prescriber will assess whether Mounjaro is suitable for your individual circumstances.
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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
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Accessing Mounjaro in the UK and Managing Treatment
In the UK, Mounjaro is available through two main routes: NHS specialist weight management services (tier 3/4) and private online prescribing. NHS access requires GP referral and assessment by specialist services, though waiting times vary significantly by region and ICB. Private access is available through GPhC-registered pharmacies following an online clinical consultation.
Mounjaro is injected once weekly, starting at 2.5 mg and increasing gradually to a maximum of 15 mg. Common side effects include nausea, diarrhoea, and stomach discomfort — these often improve over time. Use our free BMI calculator to check your current status, and our GLP-1 weight loss calculator to explore potential outcomes at different doses.
NHS guidance supports tirzepatide as part of specialist weight management services, recognising that prescription medications work best alongside lifestyle changes. Your GP can discuss whether referral to specialist services is appropriate and whether private treatment might be suitable for your situation. Always inform your prescriber of any other medications you're taking, as Mounjaro may affect how some medicines are absorbed. Track your progress with our free progress tracker if you begin treatment.
- 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 available on the NHS in the UK?
Yes, NICE has approved tirzepatide (Mounjaro) for NHS specialist weight management services. Access is through tier 3/4 specialist services, usually by GP referral. Availability varies significantly by region and waiting lists can be lengthy. Private access is available through GPhC-registered online pharmacies without NHS referral.
What is the difference between Mounjaro and Wegovy in the UK?
Both are prescription-only weight management injections. Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials showed Mounjaro may produce slightly higher average weight loss (~15–21% vs ~15% for Wegovy), though individual results vary significantly.
What are the main side effects of Mounjaro in the UK?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain. Most improve over time as your body adjusts. Serious side effects are rare but include severe stomach pain (possible pancreatitis) or allergic reactions. Always report persistent side effects to your prescriber.
Who is not eligible for Mounjaro in the UK?
Mounjaro is not suitable for people under 18, those pregnant or breastfeeding, people with a personal or family history of medullary thyroid cancer, or those with allergies to tirzepatide. It also requires careful monitoring in people with type 2 diabetes or those taking oral contraceptives.
How much weight loss can I expect with Mounjaro in the UK?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks alongside diet and exercise. Individual results vary significantly — some people lose more, some less. Weight loss depends on your starting weight, adherence to treatment, diet, and physical activity. Your prescriber will discuss realistic expectations.
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.