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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Understanding the Mounjaro Pen Click Chart in the UK
The Mounjaro KwikPen is a pre-filled injection device used for tirzepatide weight management in the UK. Each click on the pen advances the dose dial, delivering a precise amount of medication once weekly. This guide explains how the pen click system works, NHS eligibility criteria, and what to expect during dose titration — the process of gradually increasing your dose over several weeks under clinical supervision.
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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.
NHS Eligibility and the Mounjaro Dose Titration Schedule
In the UK, Mounjaro is a prescription-only medicine available through NHS specialist tier 3 weight management services or private prescribing following a clinical assessment. NICE has approved tirzepatide (Mounjaro) for use within NHS specialist weight management services for adults with a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease.
The standard Mounjaro dose titration schedule advances as follows: 2.5 mg for weeks 1–4, 5 mg for weeks 5–8, 7.5 mg for weeks 9–12, 10 mg for weeks 13–16, 12.5 mg for weeks 17–20, and 15 mg from week 21 onwards. Each KwikPen contains four pre-filled doses (a four-week supply). You must spend at least four weeks on each dose before increasing, allowing your body to adapt. In clinical trials, participants on the maximum 15 mg dose experienced average weight loss of approximately 20.9% of their body weight alongside a reduced-calorie diet and increased physical activity — though individual results vary significantly.
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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 vs Private Routes: Access and Timeline Differences
NHS access to Mounjaro is through specialist tier 3 weight management services following GP referral. Waiting lists vary significantly by region (ICB), with some areas experiencing waits of 12 months or longer. Once initiated, NHS prescriptions are significantly subsidised through prescription charges (typically £11.65 per item in England as of 2026).
Private prescribing offers faster access without NHS referral. A UK-licensed prescriber conducts an online clinical assessment, and if appropriate, issues a prescription dispensed by a GPhC-registered pharmacy. Private costs range from approximately £180–£320 per month depending on dose. Use our free GLP-1 weight loss calculator to explore potential outcomes, and the BMI calculator to determine your current eligibility based on NHS thresholds.
- 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 many clicks does each dose on a Mounjaro pen represent?
The Mounjaro KwikPen is pre-filled and does not require a UK pharmacy clicks to set doses. The pen is designed to deliver a fixed dose automatically once weekly. Each new pen in the box contains four pre-filled doses. You simply inject once weekly and dispose of the pen after four weeks of use.
What is the difference between Mounjaro and Wegovy in the UK?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro has a maximum dose of 15 mg weekly; Wegovy's maximum is 2.4 mg weekly. Clinical trials showed Mounjaro produced average weight loss of approximately 20.9% versus Wegovy's approximately 14.9% — though individual results vary and both are prescription-only.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is approved by NICE for use within NHS specialist tier 3 weight management services. You must be referred by your GP and meet eligibility criteria (BMI ≥30, or ≥27 with weight-related health conditions). Availability and waiting times vary significantly by region. Private prescribing offers faster access without NHS referral.
What are the main side effects of Mounjaro that NHS patients should expect?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — most often during dose escalation and typically improving over time. Common side effects include indigestion, fatigue, dizziness, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and allergic reactions. Always report side effects to your prescriber.
How long does it take to reach the maximum Mounjaro dose in the UK?
The standard titration schedule takes approximately 20 weeks to reach the maximum 15 mg dose, starting from 2.5 mg. Each dose is held for at least four weeks before increasing. Some patients remain on lower doses if they experience good weight loss results or prefer to minimise side effects — dose decisions are individualised based on clinical 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.