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 Are the Latest Mounjaro Rules in the UK?
Mounjaro (tirzepatide) has specific eligibility rules and prescribing guidance in the UK that determine who can access this weight loss injection and how. Understanding these rules — including NHS access, NICE approval, and prescription requirements — helps you know whether you might be eligible and what to expect when seeking treatment. This guide covers the current UK rules for Mounjaro in 2024 and how they affect your access to this dual GIP and GLP-1 receptor agonist medication.
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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 Rules for Mounjaro
Mounjaro is prescription-only in the UK and can only be prescribed by a licensed healthcare professional following a clinical assessment. NICE (National Institute for Health and Care Excellence) has approved tirzepatide for use within NHS specialist weight management services, but NHS access is limited and regional eligibility varies significantly.
- You may be eligible if you have a BMI of 30 kg/m² or above (obesity)
- Or a BMI of 27–29.9 kg/m² (overweight) with weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease
- For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply — eligibility may start at BMI 27.5 or above due to higher health risks at lower weights
- You must be aged 18 or over; Mounjaro is not approved for children or young people under 18
NHS prescribing of Mounjaro happens through specialist tier 3 and tier 4 weight management services, not through standard GP prescription. Waiting times vary greatly by region, and availability depends on your local Integrated Care Board (ICB) funding and specialist service capacity. Private prescribing is also available through GPhC-registered online clinics following a remote clinical assessment.
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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.
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Key Rules About Mounjaro Doses and Treatment
Mounjaro follows strict dose titration rules in the UK. You begin on 2.5 mg once weekly, and your dose increases by 2.5 mg every 4 weeks, up to a maximum of 15 mg weekly. Each increase requires at least 4 weeks on the current dose — you cannot escalate faster. The treatment must be combined with lifestyle changes including a reduced-calorie diet and increased physical activity; Mounjaro is not a standalone solution.
Important rules also apply to who cannot take Mounjaro: pregnant or breastfeeding women, people with a history of thyroid cancer or medullary thyroid carcinoma, those with severe gastroparesis, and anyone with a documented allergy to tirzepatide or its ingredients. Use our free GLP-1 weight loss calculator to estimate potential results at different doses, and our BMI calculator to check your starting point.
Mounjaro follows strict dose titration rules in the UK. You begin on 2.5 mg once weekly, and your dose increases by 2.5 mg every 4 weeks, up to a maximum of 15 mg weekly. Each increase requires at least 4 weeks on the current dose — you cannot escalate faster. The treatment must be combined with lifestyle changes including a reduced-calorie diet and increased physical activity; Mounjaro is not a standalone solution.
Important contraindication rules also apply: pregnant or breastfeeding women, people with a personal or family history of thyroid cancer or medullary thyroid carcinoma, those with severe gastroparesis, and anyone with documented allergy to tirzepatide cannot take this medication. Oral contraceptives require additional barrier protection for 4 weeks after each dose change due to absorption effects. Use our free GLP-1 weight loss calculator to estimate potential results at different doses, and our BMI calculator to check your current health category.
- 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 changed in Mounjaro rules for the UK in 2024?
NICE formally approved tirzepatide (Mounjaro) for NHS specialist weight management services. This means some NHS services can now prescribe it, though regional availability remains limited and eligibility criteria are strict. The main rule change emphasises specialist-led initiation only — GPs cannot prescribe Mounjaro directly in most areas. Private access remains available through licensed online prescribers.
Can I get Mounjaro on the NHS, and what are the rules?
Yes, through specialist tier 3/4 weight management services following NICE approval. However, NHS access depends on your local ICB funding and waiting lists can be very long (many regions have waiting times of 6–18 months). You must meet BMI criteria and typically need GP referral to specialist services. Private prescription is faster but costs approximately £130–£320 monthly depending on dose.
Does Mounjaro work differently to Wegovy under UK rules?
Both are prescription-only and follow similar eligibility rules, but tirzepatide (Mounjaro) is a dual GIP and GLP-1 agonist, while semaglutide (Wegovy) acts only on GLP-1. Clinical trials showed Mounjaro produced slightly higher average weight loss (~20% vs ~15%), but individual results vary greatly. Both require clinical assessment before prescription and must be combined with lifestyle changes.
Are there rules about Mounjaro side effects I should know about?
Yes — serious side effects require immediate medical attention and should be reported to your prescriber. Rules state you must stop Mounjaro and seek urgent care if you experience severe stomach pain (possible pancreatitis), serious allergic reactions, gallbladder symptoms, or vision changes. Common side effects like nausea usually improve over time but must be monitored; your prescriber may adjust your dose if side effects are severe.
What are the rules if I want to switch from Wegovy to Mounjaro?
Switching between medications must be managed by your prescriber — there is no standard conversion rule, though approximate clinical equivalences exist (e.g., Wegovy 2.4 mg roughly equates to Mounjaro 10–15 mg in effect, though this varies). Your prescriber will assess whether switching is appropriate and create a transition plan. You cannot self-switch between injections; a new prescription is required.
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