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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Mounjaro Pens — NHS Access and UK Prescribing Guide
Mounjaro pens (tirzepatide) are prescription-only injectable pens used for weight management in UK adults. They're delivered as the KwikPen — a pre-filled device containing four weekly doses. Access in the UK differs significantly between NHS and private routes, with NHS availability dependent on specialist tier 3 services and regional commissioning. This guide explains how Mounjaro pens work, who qualifies under NICE guidance, and your options for accessing treatment 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 Access and NICE Guidance for Mounjaro
NICE has approved tirzepatide (Mounjaro) for use within NHS specialist weight management services, though regional availability varies significantly. NHS access typically requires referral from your GP to a tier 3 or tier 4 specialist multidisciplinary weight management service — it is not available as standard GP prescription.
NHS eligibility criteria:
- BMI of 30 kg/m² or above (obesity), OR
- BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, prediabetes, hypertension, dyslipidaemia, sleep apnoea, or cardiovascular disease history)
- South Asian, Chinese, Black African, or Black Caribbean adults may qualify at lower BMI thresholds (27.5+)
Waiting lists for NHS specialist services can be lengthy in many areas. Your GP can advise on local availability and referral pathways. Use our free BMI calculator above to check your current BMI and understand your starting position for any referral discussion.
Clinically BackedWeight Loss
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.
Private Access vs NHS Route — Key Differences
Private access to Mounjaro pens is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber — no NHS referral needed. Private costs typically range from £150–£320 per month depending on dose, with rapid access (often within 24–48 hours of prescription). NHS access is free at point of use but involves waiting lists that may extend several months or longer depending on your regional Integrated Care Board (ICB).
Both routes require a valid prescription and clinical assessment. Your prescriber will review your medical history, current medications (especially oral contraceptives or diabetes medicines), and confirm Mounjaro is appropriate for you. Calculate your potential weight loss trajectory using our GLP-1 weight loss calculator to help inform discussions with your prescriber about realistic expectations.
- 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.
How do Mounjaro KwikPens work and how often do I inject?
Mounjaro comes as a pre-filled KwikPen containing four weekly doses. You inject once weekly (the same day each week), rotating injection sites between your stomach, thigh, or upper arm. Each pen lasts four weeks and should be stored in the fridge until first use, then can be kept at room temperature for up to 30 days.
What is NICE guidance on Mounjaro for weight loss?
NICE recommends tirzepatide for use within NHS specialist weight management services for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Access is through tier 3 specialist services, not standard GP prescription. NICE acknowledges it may offer improved outcomes compared to older weight loss medications, though individual results vary.
Am I eligible for Mounjaro on the NHS?
You may be eligible if you have a BMI of 30+ or 27+ with conditions like type 2 diabetes, hypertension, or sleep apnoea. Lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults (BMI 27.5+). Your GP can assess eligibility and refer you to your local tier 3 specialist weight management service where final prescribing decisions are made.
How quickly can I access Mounjaro privately versus NHS?
Private access typically takes 24–48 hours from prescription following an online clinical assessment. NHS access involves referral to specialist services and varies by region — waiting times can range from weeks to several months depending on local ICB commissioning and service capacity.
What dose do Mounjaro pens come in?
Mounjaro KwikPens are available in five doses: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg weekly injections. Treatment typically starts at 2.5 mg and increases by 2.5 mg every four weeks as tolerated, up to a maximum of 15 mg. Your prescriber will determine your starting dose and escalation schedule based on your individual response and tolerability.
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.