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 Pen Dosage in the UK: NHS Prescribing Guide
Mounjaro (tirzepatide) is available in the UK as a prescription-only, once-weekly injectable medication in a pre-filled KwikPen device. Understanding the correct dosage, how it's increased over time, and how NHS prescribing differs from private access is essential for anyone considering or already using this weight management treatment. This guide explains UK-specific dosing, eligibility through NHS services, and what to expect during your treatment journey.
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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.
Mounjaro Dosage Schedule and Titration in the UK
Mounjaro is dispensed in KwikPen devices, each containing four once-weekly injections. The standard UK dosing schedule starts at 2.5 mg and increases every 4 weeks if tolerated:
- Weeks 1–4: 2.5 mg once weekly (starting dose)
- Weeks 5–8: 5 mg once weekly
- Weeks 9–12: 7.5 mg once weekly
- Weeks 13–16: 10 mg once weekly
- Weeks 17–20: 12.5 mg once weekly
- Week 21 onwards: 15 mg once weekly (maximum maintenance dose)
Your prescriber may adjust this schedule based on how you tolerate each dose. Some patients remain on lower maintenance doses if side effects are significant or weight loss goals are achieved. Clinical trials, including the SURMOUNT-1 trial, showed average weight loss of approximately 20.9% body weight at the 15 mg dose alongside reduced-calorie diet and increased physical activity — though individual results vary significantly. Always use your BMI calculator to track your baseline, and monitor progress throughout treatment.
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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
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NHS Access and UK Prescribing Pathways for Mounjaro
In the UK, Mounjaro is accessed through two main routes. NHS access is via specialist tier 3 or tier 4 weight management services, typically requiring a GP referral. NICE has approved tirzepatide for use within these specialist services, but availability varies significantly by region and waiting lists can be lengthy. Private access is through GPhC-registered online pharmacies following a remote clinical assessment with a UK-licensed prescriber — no NHS referral required. Eligibility criteria are the same across both routes: BMI 30 or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease. For South Asian, Chinese, Black African, and Black Caribbean adults, lower BMI thresholds may apply. Your prescriber will assess whether tirzepatide is suitable based on your individual health profile, current medications, and weight management history.
- 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 the starting dose of Mounjaro in the UK?
The standard starting dose is 2.5 mg, given as a once-weekly injection via KwikPen. This is maintained for 4 weeks before increasing to 5 mg, provided you tolerate the initial dose. Some patients experience nausea or other side effects at the start — your prescriber may extend this phase or adjust based on your response.
How long does it take to reach the maximum Mounjaro dose?
Reaching the maximum 15 mg dose typically takes 20–21 weeks if you increase every 4 weeks without delay. However, many patients remain at lower maintenance doses (5–10 mg) if they achieve their weight loss goals or experience significant side effects. Titration is individualised based on tolerability and clinical response.
Can I skip a Mounjaro dose or adjust my dosing schedule?
No — Mounjaro must be taken exactly as prescribed, once weekly on the same day. If you miss a dose within 4 days, take it as soon as you remember and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and resume on your regular day. Never double-dose. Always contact your prescriber before changing your schedule.
Is Mounjaro dosage different on the NHS compared to private prescribing?
No — the dosage schedule and titration protocol are identical whether prescribed through NHS specialist services or private prescribers. Both follow the same MHRA-approved dosing pathway. The difference is only in access route and waiting times. Use our GLP-1 weight loss calculator to estimate potential outcomes at different doses.
What happens if I experience severe side effects at my current Mounjaro dose?
Contact your prescriber immediately. They may recommend staying on your current dose longer before escalating, reducing to a lower dose, or stopping treatment. Common side effects like nausea often improve after a few weeks on the same dose. Serious side effects (severe stomach pain, persistent vomiting, gallbladder symptoms) require urgent medical attention and possible discontinuation.
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.