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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Tips for Mounjaro: What You Need to Know
If you're considering Mounjaro (tirzepatide) or comparing it to Wegovy (semaglutide) for weight management in the UK, understanding how each works and what to expect is essential. Both are prescription-only GLP-1-based injections licensed in the UK, but they differ in mechanism, dosing, and trial outcomes. This guide covers practical tips for using Mounjaro, how it compares to Wegovy, and what a prescriber will assess when deciding which is right for you. Use our free GLP-1 weight loss calculator to explore potential outcomes with either medication.
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Calculate Your BMI Instantly
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: Key Mechanism and Trial Differences
Mounjaro (tirzepatide) works as a dual GIP and GLP-1 receptor agonist—activating two natural hormone pathways instead of one. This dual mechanism may explain its clinical trial results: participants taking the maximum 15 mg dose lost an average of 20.9% body weight in the SURMOUNT-1 trial over 72 weeks, alongside a reduced-calorie diet and increased activity.
Wegovy (semaglutide) is a GLP-1-only agonist. In the STEP-1 trial, participants on 2.4 mg lost an average of 14.9% body weight over 68 weeks under similar lifestyle conditions. Both are effective, but Mounjaro's dual action may offer slightly higher average weight loss in clinical settings.
- Mounjaro: starts at 2.5 mg, escalates to maximum 15 mg over 20 weeks
- Wegovy: starts at 0.25 mg, escalates to maximum 2.4 mg over 16 weeks
- Both require minimum 4-week intervals between dose increases
- Individual results vary significantly regardless of medication choice
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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.
Practical Tips and Prescriber Assessment Criteria
Both Mounjaro and Wegovy require a UK-licensed prescriber's assessment before prescription. Your GP or specialist will review your medical history, current medications, weight-related conditions (such as type 2 diabetes, high blood pressure, or sleep apnoea), and eligibility based on BMI. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds may apply due to higher health risks at lower weights.
Practical tips for either medication: start with the lowest dose to allow your body to adjust; take the injection at the same time each week; rotate injection sites (stomach, thigh, or upper arm) to prevent irritation; stay hydrated; eat smaller, frequent meals as appetite naturally decreases; report persistent nausea or other side effects to your prescriber—dose adjustment or switching medications is an option. Use our BMI calculator to understand your current health category and discuss suitability with your prescriber.
- 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 more effective than Wegovy?
Clinical trials show Mounjaro achieved slightly higher average weight loss (20.9% vs 14.9%), but individual results vary greatly. Effectiveness depends on your body, adherence, diet, and activity level. Only a prescriber can determine which is more suitable for you based on your health profile.
Can I switch from Wegovy to Mounjaro?
Yes, switching is possible and managed by your prescriber. There's no official conversion chart, but approximate equivalence exists (e.g., Wegovy 2.4 mg ≈ Mounjaro 10 mg). Any switch must be supervised by your prescriber to ensure safe transition and appropriate dosing.
What dose of Mounjaro should I start with?
Mounjaro always starts at 2.5 mg once weekly for the first 4 weeks. Your prescriber increases the dose by 2.5 mg every 4 weeks if tolerated, up to a maximum of 15 mg. Never increase doses yourself—follow your prescriber's guidance based on your response and side effects.
How long does it take to see weight loss results with Mounjaro?
Most people notice appetite changes within 1–2 weeks, but meaningful weight loss typically becomes apparent after 4–8 weeks of consistent use alongside diet and activity changes. Clinical trials measured results over 72 weeks—weight loss is a gradual process, not immediate.
Will my GP prescribe Mounjaro on the NHS or must I go private?
NHS prescription is through specialist tier 3 weight management services (referral required, regional availability varies). Private online prescribing is available without NHS referral through GPhC-registered pharmacies following a clinical assessment. Availability and cost differ by route—discuss options with your GP first.
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.