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
Free tracker included with every download this week
What Is Half Dose Mounjaro?
Half dose Mounjaro typically refers to the 2.5 mg starting dose used during the initial four weeks of treatment. This is the lowest available dose in the Mounjaro tirzepatide range and is designed to help your body adjust to the medication before gradually increasing to higher doses. The NHS and private prescribers in the UK use this gradual dose titration approach to minimise side effects and assess individual tolerance. Understanding how Mounjaro dosing works helps you know what to expect when starting this prescription-only 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.
How Mounjaro Dose Titration Works
Mounjaro uses a structured dose escalation schedule. You start at 2.5 mg once weekly for the first four weeks. Each KwikPen device contains four doses, so your first pen covers one month of treatment.
After four weeks at the starting dose, your prescriber will assess your response and tolerance. If you're tolerating the medication well, the dose increases to 5 mg for weeks 5–8. From there, further increases occur every four weeks: 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg (the maximum dose). This gradual approach, called dose titration, allows your body to adapt and helps manage common side effects like nausea and stomach discomfort. Individual titration schedules may vary — your prescriber may keep you on a particular dose longer if needed.
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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.
Who Gets Half Dose and What Happens Next
All adults starting Mounjaro in the UK begin with the 2.5 mg half dose, regardless of their BMI, weight, or health conditions. This is standard practice for prescription weight loss injections using tirzepatide, and it's the same approach used with Mounjaro KwikPen devices across NHS specialist services and private prescribing pathways.
Your prescriber will review your progress at four-week intervals. If side effects are minimal and you're tolerating the medication, your dose will increase. If you're experiencing significant nausea or other effects, your prescriber may keep you on 2.5 mg longer or increase more slowly. This personalised approach differs from fixed dosing — there's no "one size fits all" with Mounjaro UK prescription protocols.
- 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.
Why does Mounjaro start with a half dose?
The 2.5 mg starting dose allows your body to adapt to tirzepatide gradually. This minimises side effects like nausea and helps prescribers assess how you tolerate the medication before increasing further. Clinical evidence supports this cautious approach for safety.
How long do you stay on half dose Mounjaro?
You remain on 2.5 mg for four weeks. After that, if you're managing side effects well, your dose increases to 5 mg. Your prescriber may extend the starting dose period if you're experiencing significant effects.
Is half dose Mounjaro effective for weight loss?
The 2.5 mg starting dose is not designed for weight loss itself — it's a tolerance phase. Weight loss typically becomes noticeable at 5 mg and higher doses. Clinical trials show most weight loss occurs at maintenance doses of 10 mg and above.
How does Mounjaro compare to Wegovy for half dosing?
Wegovy starts at 0.25 mg (much lower in absolute terms) because it's a different medication with different potency. Mounjaro vs Wegovy have different dose ranges entirely. Both use gradual titration, but follow different schedules and escalation timelines.
Can you stay on half dose Mounjaro long-term?
The 2.5 mg dose is intended as a starting phase only, typically for four weeks. Staying on this dose long-term is unusual, though some people may be kept here temporarily if side effects are challenging. Your GP or prescriber will guide the right schedule for you.
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.