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? A UK Health Guide
Monjaro is a prescription-only weekly injection licensed in the UK for weight management in adults. Its active ingredient is tirzepatide, a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways to help regulate appetite and support weight loss. Unlike some other weight loss medications, Monjaro works through a dual mechanism, which distinguishes it from single-action GLP-1 agonists. This guide explains how Monjaro works, who may be eligible, and how to access it through NHS or private services 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 NHS Eligibility
How Monjaro works: Monjaro activates two hormone pathways—GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1)—which help reduce appetite, support feeling fuller after smaller meals, and slow how quickly food leaves the stomach. This dual mechanism may contribute to its potential effectiveness.
NHS eligibility for Monjaro: You may be eligible for NHS-prescribed Monjaro if you are an adult with:
- A BMI of 30 kg/m² or above (obesity), OR
- A BMI of 27–29.9 kg/m² (overweight) with at least one weight-related health condition such as type 2 diabetes, hypertension, abnormal blood fats, sleep apnoea, or cardiovascular disease history
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply. Access is through specialist tier 3 weight management services, typically following a referral from your GP—availability varies significantly by region.
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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.
NHS vs Private Routes for Monjaro in the UK
NHS access: NICE has approved tirzepatide for use within NHS specialist weight management services. However, prescribing through the NHS is limited to tier 3 and tier 4 specialist services, not standard GP practices. You'll need a GP referral and an assessment by the specialist team. Many areas have lengthy waiting lists—in some regions, waiting times exceed 12 months.
Private access: Monjaro is available through GPhC-registered online prescribing services following a clinical assessment by a UK-licensed prescriber. This route doesn't require NHS referral and tends to offer faster access. Costs vary by dose and provider, typically ranging from £130–£300 monthly. Use our free GLP-1 weight loss calculator above to explore projected 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.
Is Monjaro the same as Wegovy?
No. Both are prescription-only weight loss injections licensed in the UK, but Monjaro contains tirzepatide (dual GIP+GLP-1 agonist), while Wegovy contains semaglutide (GLP-1 agonist only). Clinical trials showed Monjaro achieved slightly higher average weight loss (~20.9% at maximum dose) compared to Wegovy (~14.9%), though individual results vary significantly.
What dose does Monjaro start at?
Monjaro starts at 2.5 mg once weekly. Your prescriber will increase the dose gradually every 4 weeks—the maximum is 15 mg once weekly. Each KwikPen contains 4 doses (4 weeks' supply). Dose adjustments are based on tolerance and response.
Can I get Monjaro on the NHS?
Yes, through specialist tier 3 weight management services following a GP referral and clinical assessment. However, NHS prescribing is limited and varies by region. Waiting lists can be very long. Private prescribing offers faster access through online clinical assessments with UK-licensed prescribers.
What are the main side effects of Monjaro?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain—usually mild and reduce over time as the body adjusts. Less common side effects include headache, fatigue, and injection site reactions. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) requiring immediate medical attention.
How much weight will I lose on Monjaro?
Clinical trials (SURMOUNT-1) showed average weight loss of approximately 15–21% of body weight at the maximum 15 mg dose, achieved alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly based on genetics, diet adherence, exercise, and other factors. Use our BMI calculator above to check your current weight category and understand your personalised health context.
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.