The UK's most complete GLP-1 guide
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- 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 New Rules and Changes in the UK
Mounjaro (tirzepatide) regulations and prescribing rules in the UK have been clarified following NICE approval and NHS guidance updates. If you're considering this weight loss injection, it's important to understand the current eligibility criteria, how to access it, and what has changed. This guide explains the latest rules, whether through NHS specialist services or private prescription routes, and helps you understand if Mounjaro might be suitable for you.
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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.
Current UK Eligibility and Access Rules for Mounjaro
NICE approval: Mounjaro (tirzepatide) was approved by NICE for use within NHS specialist weight management services. It is available through tier 3 and tier 4 weight management services for eligible adults.
- BMI of 30 kg/m² or above, OR
- BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, high blood pressure, sleep apnoea, cardiovascular disease, or abnormal blood fats)
- For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds apply: BMI 27.5 or above
Prescribers must assess each patient individually. Mounjaro is prescription-only and requires a clinical assessment before dispensing. Private access through GPhC-registered online pharmacies is also available following an online clinical consultation with a UK-licensed prescriber. Private access typically offers faster availability than NHS routes, which often have waiting lists of several months in many regions.
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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.
Key Prescribing Changes and Restrictions to Know
Recent changes have clarified that Mounjaro must not be prescribed to pregnant women or those breastfeeding. Women of reproductive age taking oral contraceptives should use barrier methods or switch to non-oral contraception for 4 weeks after starting Mounjaro and 4 weeks after each dose increase — this reflects updated guidance on oral medication absorption. Doses now follow strict titration: starting at 2.5 mg, with minimum 4-week intervals before escalation. The maximum dose remains 15 mg once weekly. Patients taking other medications, especially diabetes drugs or oral contraceptives, must inform their prescriber to check for interactions. All prescribers must monitor for serious side effects including signs of pancreatitis (severe stomach pain spreading to the back) and adjust or stop treatment if complications arise.
- 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 main change to Mounjaro rules in the UK?
NICE approval has clarified Mounjaro is available through NHS specialist weight management services for eligible adults with BMI 30+ or BMI 27–29.9 with weight-related health conditions. This replaced previous uncertainty about NHS access. Private prescription routes have also expanded, offering faster access. The key change is official NHS recognition, though regional availability remains variable.
Can I get Mounjaro on the NHS now?
Yes, Mounjaro is NICE-approved for NHS specialist services (tier 3/4). However, NHS access depends on your ICB region and current waiting lists, which vary significantly. Many regions have waiting lists of months to years. Private prescription remains the fastest route through GPhC-registered online pharmacies following an online clinical assessment.
Am I eligible if I have a BMI of 28 and prediabetes?
Yes, you may be eligible. The rule is BMI 27–29.9 with a weight-related health condition. Prediabetes qualifies. However, a prescriber must assess your individual health situation. Use our free BMI calculator to check your exact BMI, then discuss eligibility with your GP or an online prescriber.
Has the Mounjaro dose titration schedule changed?
The titration schedule remains consistent: start 2.5 mg, increase by 2.5 mg every 4 weeks, up to a maximum of 15 mg. No recent changes to this protocol. Each dose is a once-weekly injection. Your prescriber will guide the schedule based on your response and tolerance.
What happens if I'm pregnant or want to become pregnant?
Mounjaro must not be used during pregnancy or whilst breastfeeding. If you're planning pregnancy, discuss with your prescriber at least 3 months in advance. Women of reproductive age on Mounjaro should use effective contraception (ideally barrier methods or non-oral contraception) due to reduced absorption of oral contraceptives during tirzepatide treatment.
Ready to take control of your weight loss journey?
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