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 Prescribing Guidelines in the UK
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK, but access follows specific prescribing guidelines. Understanding who is eligible, how doses are managed, and the difference between NHS and private prescribing can help you navigate the treatment pathway. This guide explains the UK prescribing framework based on current NICE guidance and clinical practice.
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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.
UK Eligibility and Prescribing Criteria
NHS prescribing guidelines for Mounjaro specify that adults are eligible if they have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, prediabetes, hypertension, dyslipidaemia, obstructive sleep apnoea, or cardiovascular disease history. For people of South Asian, Chinese, Black African, or Black Caribbean descent, lower BMI thresholds apply — eligibility may start at BMI 27.5 or above due to higher metabolic risk at lower weights.
- Age: 18 years or older
- Not pregnant, planning pregnancy, or breastfeeding
- No contraindications (e.g. severe gastroparesis, personal or family history of medullary thyroid cancer)
- Prescribed within tier 3 specialist weight management services on the NHS, or through private assessment with a UK-licensed prescriber
NICE has approved tirzepatide for use within NHS specialist services, though regional availability varies significantly and waiting lists can be lengthy.
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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.
Dose Titration and Clinical Management
Mounjaro uses a gradual dose escalation schedule starting at 2.5 mg once weekly, with increases every 4 weeks (minimum): 2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg. Your prescriber will adjust your dose based on tolerance and response, monitoring for side effects like nausea or gastrointestinal symptoms. Each KwikPen contains 4 weekly doses. Calculate your potential weight loss trajectory using our GLP-1 weight loss calculator to understand projected outcomes at different doses.
Patients should attend regular follow-up appointments (typically 4–12 weekly) to assess efficacy and manage side effects. Mounjaro requires lifestyle changes — reduced-calorie diet and increased physical activity — to achieve best results. If you switch from Wegovy or another GLP-1 medication, your prescriber will guide the transition carefully.
Regular monitoring includes blood pressure checks, metabolic markers, and symptom review. If side effects persist beyond 4 weeks at a dose, your prescriber may reduce or pause treatment. Use our free BMI calculator above to track your BMI changes throughout treatment, and our progress tracker to log weight loss and monitor your response to Mounjaro over time. Always inform your GP or prescriber of all medications you take — Mounjaro may affect absorption of oral contraceptives and some diabetes medicines.
- 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 I get Mounjaro prescribed on the NHS in the UK?
Request a referral from your GP to your local tier 3 specialist weight management service. You'll be assessed against NICE criteria (BMI ≥30, or ≥27 with comorbidities). NHS availability varies by region; some services have long waiting lists. Private prescribing is faster — available through online assessment with a UK-licensed prescriber.
What is the difference between Mounjaro and Wegovy prescribing?
Both are once-weekly injections for weight management, but Mounjaro is a dual GIP+GLP-1 agonist while Wegovy (semaglutide) is GLP-1 only. Clinical trials showed Mounjaro achieved slightly higher average weight loss (~15–21% vs ~15% for Wegovy). Starting doses differ: Mounjaro starts at 2.5 mg, Wegovy at 0.25 mg. Both follow similar eligibility criteria.
Can I switch from another weight loss medication to Mounjaro?
Yes, your prescriber can transition you from Wegovy, Saxenda, or other GLP-1 medications to Mounjaro. However, there is no official conversion chart — your prescriber will manage the switch carefully, typically starting at a low Mounjaro dose (2.5 mg) and titrating gradually. Do not change medications without guidance.
What happens if I have side effects during Mounjaro dose escalation?
Common side effects (nausea, constipation, diarrhoea) often improve within days to weeks as your body adjusts. If side effects persist after 4 weeks at a dose, inform your prescriber — they may pause, reduce, or adjust your dose. Staying hydrated, eating small frequent meals, and avoiding fatty foods can help manage gastrointestinal symptoms.
Does my BMI need to be checked before Mounjaro is prescribed?
Yes. Your prescriber will calculate your BMI using your height and weight to confirm eligibility. Use our free BMI calculator above to check your personal BMI before your appointment — this helps you understand whether you meet the NHS or private prescribing thresholds for Mounjaro treatment.
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.