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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What Is Moinjaro and How Does It Work?
Moinjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight with related health conditions. It's a dual GIP and GLP-1 receptor agonist — meaning it works on two natural hormone pathways to help regulate appetite and support feeling fuller after meals. Unlike some weight loss medications, Moinjaro is administered once weekly as a pre-filled injection pen. Understanding how it works and whether you might be eligible can help you make informed decisions about your health with your GP.
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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 Moinjaro Works and Key Features
Moinjaro's dual mechanism activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptor pathways. This dual action may help suppress appetite, reduce food cravings, and support feeling satisfied with smaller portions. It also slows gastric emptying, meaning food moves through your stomach more slowly — though this effect typically reduces over time.
Key features of Moinjaro in the UK:
- Once-weekly pre-filled KwikPen injection
- Starting dose of 2.5 mg, escalating to a maximum of 15 mg weekly
- Prescription-only — requires clinical assessment before being prescribed
- Subject to additional MHRA monitoring (Black Triangle ▼ status)
- Clinical trials showed average weight loss of 15–21% of body weight alongside a reduced-calorie diet and increased physical activity
- Individual results vary significantly
The injectable format and once-weekly dosing make it convenient for many people managing their weight long-term.
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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.
UK Eligibility and Getting Moinjaro
In the UK, you may be eligible for Moinjaro if you have 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, prediabetes, high blood pressure, or cardiovascular disease. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher health risks at lower weights.
Access in the UK is through NHS specialist tier 3/4 weight management services (via GP referral) or private prescribing through registered online clinics. NHS waiting lists vary significantly by region. Your GP or a licensed prescriber will assess whether Moinjaro is suitable for your individual circumstances, medical history, and current medications. Use our free BMI calculator above to check your current BMI and understand where you sit on the NHS guidance scale.
- 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's the difference between Mounjaro and Wegovy?
Both are prescription weight loss injections licensed in the UK, but they work differently. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro starts at 2.5 mg and goes up to 15 mg weekly. Wegovy starts at 0.25 mg and goes up to 2.4 mg weekly. Clinical trials showed slightly higher average weight loss with Mounjaro, but individual results vary. Your prescriber will assess which is more suitable for you.
How quickly will I lose weight on Mounjaro?
Weight loss with Mounjaro is gradual and individual. Clinical trials showed average losses of 15–21% of body weight over around 72 weeks, but this varies significantly between people. The NHS recommends losing weight at a rate of 0.5–1 kg per week for sustainable results. Mounjaro works best alongside a reduced-calorie diet and increased physical activity — it's a support tool, not a replacement for lifestyle changes.
What are the most common side effects of Mounjaro?
The most common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain, especially when starting or increasing doses. These often improve over time as your body adjusts. Injection site reactions like redness or bruising can occur. If you experience severe, persistent stomach pain spreading to your back (possible pancreatitis) or serious allergic reactions, seek immediate medical attention and contact your GP.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is approved by NICE for use within NHS specialist weight management services (tier 3/4). However, access requires referral from your GP and varies significantly by region — waiting lists can be several months to over a year in some areas. Private prescribing through registered online clinics offers faster access but involves costs. Ask your GP about availability in your area.
Do I need to stay on Mounjaro forever?
Mounjaro is typically used for as long as it's helping you manage your weight and you remain eligible. Some people use it for 6–12 months or longer. If you stop Mounjaro, weight regain can occur, which is why it's often combined with long-term lifestyle changes. Your prescriber will discuss duration and monitoring with you based on your individual goals and health situation.
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.