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 Pens and NHS Access in the UK
Monjaro pens contain tirzepatide, a dual GIP and GLP-1 receptor agonist approved in the UK for weight management. Access through the NHS requires referral to specialist tier 3 weight management services and meets specific BMI and health criteria. This guide explains NHS eligibility, how the KwikPen device works, and what to expect when seeking Monjaro through the NHS in the UK.
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Calculate Your BMI Instantly
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.
NHS Eligibility and Specialist Tier 3 Services
Monjaro is available through the NHS for adults who meet specific eligibility criteria assessed by specialist tier 3 weight management services. You must have a BMI of 30 kg/m² 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, or sleep apnoea).
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher cardiovascular risk at lower weights. To access Monjaro through the NHS, your GP refers you to your regional tier 3 specialist weight management service. These services provide comprehensive support including dietary advice, behavioural coaching, and medical monitoring alongside prescription medication. NHS access varies significantly by region and ICB (Integrated Care Board), with waiting lists potentially extending several months in many areas.
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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.
How Monjaro Pens Work and NHS Monitoring
Monjaro comes in a pre-filled KwikPen device — a once-weekly self-injection pen available in doses from 2.5 mg up to 15 mg. The dual GIP/GLP-1 mechanism helps regulate appetite and supports feeling fuller after smaller meals. Your specialist service will start you at the lowest dose (2.5 mg) and increase gradually based on your response and tolerability.
NHS specialist teams monitor your progress through regular appointments, checking weight loss, side effects, and overall health. You'll work alongside dietitians and weight management specialists to ensure you combine Mounjaro with sustainable dietary changes and increased physical activity. Use our free GLP-1 weight loss calculator to see potential projection outcomes at different doses.
NHS vs Private Access: The NHS route provides comprehensive specialist support and monitoring but involves referral, assessment, and potential waiting lists. Private prescribing through GPhC-registered online pharmacies offers faster access without NHS referral, though costs are not covered by the NHS. Both routes require a clinical assessment to confirm suitability. Your choice depends on your circumstances, timeline, and preference for specialist NHS support versus faster private access.
- 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 is Monjaro and how does it work?
Monjaro contains tirzepatide, a dual GIP and GLP-1 receptor agonist that activates two natural hormone pathways to help regulate appetite and support feeling fuller. It comes as a once-weekly pre-filled KwikPen injection. In clinical trials, Monjaro helped people lose an average of 15–21% of their body weight, though individual results vary and are achieved alongside dietary changes and physical activity.
How do I access Monjaro through the NHS in the UK?
Ask your GP for a referral to your regional tier 3 specialist weight management service. You'll need a BMI of 30 or above, or 27–29.9 with weight-related health conditions. The specialist team will assess your suitability, provide comprehensive support, and monitor your progress throughout treatment.
What are the main side effects of Monjaro?
Common side effects include nausea, diarrhoea, vomiting, and constipation — often temporary and reducing over time. Serious side effects are rare but may include severe stomach pain (possible pancreatitis) or gallbladder problems. Report any serious symptoms to your NHS team immediately.
How long does it take to receive Monjaro on the NHS?
Waiting times vary significantly by region and ICB. Initial GP referral to tier 3 services can take weeks. Once assessed by the specialist team, Monjaro may be initiated quickly, but some areas have longer waiting lists. Private prescribing typically offers faster access if you choose that route.
Can I use our BMI calculator to check if I might be eligible?
Yes — use our free BMI calculator to check your current BMI. If you have a BMI of 27 or above, you may be eligible for assessment by a specialist service, especially if you have weight-related health conditions. Your GP and specialist team will make the final decision based on your individual health circumstances.
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.