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 Monjaro? UK Guide to Tirzepatide Weight Management
Monjaro is a prescription-only weight management injection licensed in the UK that contains tirzepatide, a dual GIP and GLP-1 receptor agonist. This means it works on two natural hormone pathways to help regulate appetite and support weight loss alongside a reduced-calorie diet and increased physical activity. Given once weekly as a pre-filled KwikPen injection, Monjaro has shown promising results in clinical trials. In this guide, we explain how it works, who's eligible, what to expect, and how to access it through the NHS or privately 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.
How Monjaro Works and What Makes It Different
Monjaro is unique because it's a dual GIP and GLP-1 receptor agonist — unlike other weight loss injections such as Wegovy (semaglutide), which only activate the GLP-1 pathway. By stimulating both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors, Monjaro may help regulate appetite more effectively.
- Reduces hunger signals and food cravings
- Helps you feel fuller after eating smaller portions
- Slows how quickly food leaves your stomach
- Supports better blood sugar control
- Available as a once-weekly injection
In the SURMOUNT-1 clinical trial, participants taking Monjaro at the maximum 15 mg dose lost an average of around 20.9% of their body weight over 72 weeks — though individual results vary significantly and results were achieved alongside a reduced-calorie diet and increased physical activity. Our free GLP-1 weight loss calculator can help you explore potential weight loss outcomes at different doses.
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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, Doses, and How to Access Monjaro
Eligibility for Monjaro in the UK: You may be eligible if you have a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply. You cannot take Monjaro if you're under 18, pregnant, breastfeeding, or allergic to tirzepatide.
Monjaro doses start at 2.5 mg and increase gradually every 4 weeks, up to a maximum of 15 mg once weekly. Use our free BMI calculator above to check your starting BMI and understand where you sit on NHS health guidelines. Access is available through NHS specialist tier 3 weight management services (waiting times vary by region) or privately through GPhC-registered online pharmacies following a clinical assessment.
- 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 are the main side effects of Monjaro?
Very common side effects include nausea, diarrhoea, vomiting, and stomach pain — usually most noticeable when starting or increasing doses. Less common side effects are fatigue, dizziness, and injection site reactions. Most side effects improve over time. Seek urgent medical attention for severe stomach pain (possible pancreatitis), serious allergic reactions, or changes in vision.
How much weight can I expect to lose on Monjaro?
In clinical trials, participants lost an average of 15–21% of body weight depending on dose and adherence to diet and activity changes. However, individual results vary significantly. Your GP or prescriber can discuss realistic expectations based on your personal health and circumstances.
Can I get Monjaro on the NHS in the UK?
Monjaro is approved for NHS use through specialist tier 3 weight management services. You'll need a GP referral and assessment. Availability and waiting times vary significantly by region and local integrated care board (ICB). Alternatively, Monjaro is available privately through GPhC-registered online pharmacies.
How is Monjaro different from Wegovy?
Monjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) activates only the GLP-1 pathway. Monjaro reaches a higher maximum dose (15 mg vs 2.4 mg) and clinical trials suggest slightly higher average weight loss, but both are effective. The right choice depends on your individual health profile and GP recommendation.
How often do I inject Monjaro, and where?
Monjaro is injected once weekly using a pre-filled KwikPen. You can inject into your stomach, upper thigh, or upper arm (upper arm requires assistance). Rotate injection sites each week. Each pen contains 4 weekly doses. Store unopened pens in the fridge at 2–8°C, or at room temperature for up to 30 days after first use.
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.