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 Get The Most Out Of Mounjaro: A UK Comparison Guide
Getting the most out of Mounjaro (tirzepatide) depends on understanding how it works, how it compares to alternatives like Wegovy, and what you can control to support your weight loss journey. This guide explains the key differences between these two weight loss injections, the clinical evidence behind each, and how to work with your prescriber to optimise your results. Whether you're considering which medication might suit you better, or you're already taking Mounjaro, understanding the science helps you make informed decisions about your treatment.
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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 vs Wegovy: Clinical Evidence And Mechanism Differences
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both once-weekly GLP-1-based injections licensed in the UK for weight management, but they work through different mechanisms. Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways simultaneously — the GIP pathway (glucose-dependent insulinotropic polypeptide) and the GLP-1 pathway. Wegovy activates GLP-1 only.
Clinical trial data shows different outcomes: The SURMOUNT-1 trial showed Mounjaro users lost an average of 20.9% of their body weight at the maximum 15 mg dose over 72 weeks. The STEP-1 trial showed Wegovy users lost approximately 14.9% of their body weight at the 2.4 mg dose over 68 weeks. However, individual results vary significantly — these are trial averages, not assures. Both medications are most effective when combined with reduced-calorie diet and increased physical activity, following a reduced-calorie diet and increased physical activity.
The dual mechanism of Mounjaro may offer additional benefits for some patients, but this does not automatically make it "better" — suitability is individual and should be determined by your prescriber following clinical assessment.
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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, Side Effects, And Individual Suitability
Both medications use gradual dose titration — you start on a low dose and increase weekly until reaching an effective dose. Mounjaro starts at 2.5 mg and increases over several weeks up to a maximum of 15 mg. Wegovy starts at 0.25 mg and titrates up to 2.4 mg over approximately 16 weeks. Slower titration gives your body time to adjust and may reduce side effects like nausea or diarrhoea.
Getting the most out of either medication involves: following dose escalation exactly as prescribed (do not skip ahead or extend doses), maintaining a reduced-calorie diet (the injection alone does not cause weight loss without dietary changes), reporting side effects promptly (your prescriber may adjust your dose if side effects are severe), and staying consistent (take your weekly injection on the same day each week). Whether Mounjaro or Wegovy is prescribed depends on your individual health profile, previous treatment response, and prescriber guidance — both require a UK prescription and clinical assessment.
- 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.
Is Mounjaro better than Wegovy for weight loss?
Clinical trials show different average outcomes — Mounjaro showed approximately 20.9% average weight loss, Wegovy approximately 14.9% — but individual results vary significantly. "Better" depends on your personal health profile, medical history, and how your body responds. Your prescriber will assess which is more suitable for you. Neither is universally superior; suitability is individual.
Can I switch from Wegovy to Mounjaro if I'm not seeing results?
Any medication switch must be managed by your prescriber. If you've been on Wegovy for at least 12 weeks at an effective dose without satisfactory results, discuss this with your GP or prescriber. They may adjust your current dose, suggest lifestyle changes, or discuss switching to Mounjaro — but this requires clinical reassessment and a new prescription.
What's the difference between GLP-1 and GIP/GLP-1?
Wegovy is a GLP-1 receptor agonist (activates one hormone pathway). Mounjaro is a dual GIP and GLP-1 receptor agonist (activates two pathways). The dual mechanism of Mounjaro may provide additional appetite and metabolic benefits for some people, but both are effective. Your prescriber will choose based on your individual needs.
How long does it take to see results with Mounjaro?
Most people notice appetite reduction within the first 1–2 weeks. Measurable weight loss typically becomes apparent after 4–8 weeks. However, this varies — some people see slower initial changes. Consistency with dose titration, diet, and physical activity is essential. Use our free GLP-1 weight loss calculator to estimate potential outcomes based on your starting weight and dose.
What should I do if I experience side effects on Mounjaro?
Common side effects like nausea and diarrhoea often reduce as your body adjusts. Stay hydrated, eat smaller meals, and avoid fatty or high-sugar foods. Report persistent or severe side effects to your prescriber — they may slow dose escalation or suggest temporary strategies. Serious side effects like severe stomach pain require urgent medical attention.
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.