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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Monjaro UK Health Guide
Monjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight with health conditions. This UK health guide covers how it works, NHS eligibility criteria, side effects, and access routes. It's a dual GIP and GLP-1 receptor agonist, meaning it works differently from other weight loss injections. Understanding the facts about Monjaro helps you make informed decisions about whether it might be suitable for you. Always consult your GP or a healthcare professional before considering any weight management treatment.
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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 Monjaro Works and UK Eligibility
How Monjaro works: Monjaro activates two natural hormone pathways — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual action may help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. It also slows gastric emptying, though this effect typically reduces over time.
UK eligibility: You may be eligible for Monjaro if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, sleep apnoea, or cardiovascular disease. Lower thresholds may apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, where NHS guidance recommends eligibility starting at BMI 27.5 or above due to higher health risks at lower BMI levels.
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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
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Side Effects and What to Expect
Common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — these often improve as your body adjusts. Less common effects include indigestion, fatigue, dizziness, injection site reactions, and temporary hair loss. Most people experience some nausea initially, particularly when starting or increasing doses. Serious side effects are rare but require urgent medical attention: severe stomach pain spreading to the back (possible pancreatitis), gallbladder problems, serious allergic reactions, or changes in vision. Always report any concerning symptoms to your GP or prescriber immediately.
- 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 Monjaro available on the NHS in the UK?
Yes, NICE has approved tirzepatide (Monjaro) for NHS use through specialist weight management services (tier 3/4). However, NHS access varies significantly by region and involves referral from your GP. Waiting lists can be lengthy in many areas. Private prescription access is also available through UK-licensed online prescribers and GPhC-registered pharmacies.
What dose of Monjaro would I start on?
The standard starting dose in the UK is 2.5 mg once weekly for the first four weeks. Your prescriber will then increase the dose gradually — typically by 2.5 mg every four weeks — up to a maximum of 15 mg per week. Each dose is a pre-filled injection pen containing four weeks' supply.
How much weight loss can I expect from Monjaro?
Clinical trials (SURMOUNT-1) showed average weight loss of 15–21% of body weight at the highest dose over 72 weeks, alongside a reduced-calorie diet and increased physical activity. However, individual results vary significantly. Weight loss is not guaranteed, and some people respond better than others. Your healthcare professional can discuss realistic expectations based on your circumstances.
Can I use Monjaro if I'm taking other medications?
Monjaro may interact with some medications. Importantly, if you're taking oral contraceptives, add a barrier method or switch contraception for four weeks after starting and after each dose increase, as Monjaro may reduce oral medication absorption. Always inform your prescriber of all medications you take so they can assess compatibility before prescribing.
What's the difference between Monjaro and Wegovy?
Monjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1-only agonist. Monjaro typically shows slightly higher average weight loss in trials (~21% vs ~15% body weight), but individual results vary considerably. Both are once-weekly injections. The right choice depends on your individual health profile, assessed by your prescriber.
Ready to take control of your weight loss journey?
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