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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How To Half Dose Mounjaro In The UK
If you're taking Mounjaro (tirzepatide) in the UK and wondering whether you can half your dose, the answer depends on your individual circumstances and your prescriber's guidance. Mounjaro uses a specific dose titration schedule, and adjusting doses should only be done under medical supervision. This guide explains the official dosing protocol, when dose adjustments might be appropriate, and why speaking to your GP or the prescriber who issued your Mounjaro prescription is essential before making any changes.
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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.
Understanding Mounjaro Dosing And Titration
Mounjaro is delivered as once-weekly injections using a pre-filled KwikPen device, with each pen containing four doses (a four-week supply). The tirzepatide dosing schedule is designed to build up gradually to minimise side effects whilst maximising effectiveness.
- Weeks 1–4: 2.5 mg (starting dose)
- Weeks 5–8: 5 mg (first escalation)
- Weeks 9–12: 7.5 mg (second escalation)
- Weeks 13–16: 10 mg (third escalation)
- Weeks 17–20: 12.5 mg (fourth escalation)
- Week 21+: 15 mg (maximum maintenance dose)
Each dose must be used for at least four weeks before increasing. The KwikPen device is pre-filled with a fixed dose — you cannot physically half a single injection. If you need a lower dose, this requires a new prescription for a lower-dose pen or a different formulation approach.
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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.
When Dose Adjustments May Be Appropriate
There are clinical situations where a prescriber might recommend staying on a lower dose or adjusting your dosing schedule:
- Persistent side effects: If nausea, diarrhoea, or other gastrointestinal symptoms are severe, your prescriber may slow the titration or reduce your dose rather than escalating further
- Individual tolerance: Some people experience good weight loss results at lower doses (5 mg or 7.5 mg) and may not need to escalate to the maximum 15 mg dose
- Medication interactions: Certain medications or health conditions may require dose adjustment
- Kidney or liver function: Reduced kidney or liver function might affect dosing recommendations
Any dose adjustment must be made by your prescriber — never attempt to physically divide or half an injection yourself. Track your progress using our free progress tracker to share detailed results with your GP or prescriber when discussing dosing.
- 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.
Can you physically half a Mounjaro KwikPen injection?
No. Mounjaro KwikPens are pre-filled with fixed doses and are designed to deliver the full dose when used. You cannot split or half an individual injection. If you need a lower dose, speak to your prescriber about requesting a lower-dose pen or adjusting your titration schedule.
What if Mounjaro side effects are too severe?
Contact your prescriber immediately. They may recommend slowing your dose titration, staying on your current dose longer, or reducing your dose. Never stop taking Mounjaro suddenly without medical advice. Your GP or the prescriber who issued your prescription can adjust your treatment plan safely.
Is there a minimum effective dose of Mounjaro?
Many people see weight loss results at lower doses (5 mg to 7.5 mg). Clinical trial data showed weight loss at all dose levels, though higher doses typically showed greater average weight loss. Your prescriber can help determine the lowest effective dose for you based on your individual response.
Can you skip a dose instead of halving it?
You should not skip doses without medical guidance, as this can affect your treatment consistency. If you've missed a dose, take it within four days. More than four days late? Skip that dose and take your next one on schedule. Always discuss any concerns with your prescriber.
How do I know if my Mounjaro dose is right for me?
Use our GLP-1 weight loss calculator to track your projected results at your current dose, and use our BMI calculator to monitor your progress over time. Keep detailed records to share with your GP or prescriber — they can assess whether your dose is working effectively and whether adjustments are needed based on your health outcomes.
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.