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
Mounjaro Facts vs Wegovy: What's the Difference?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both prescription-only weight loss injections licensed in the UK, but they work differently and have different clinical profiles. This guide compares the key facts about each medication based on NHS-aligned information and clinical trial data, helping you understand how they differ and what questions to ask your GP or prescriber. Both require a clinical assessment before prescription.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Clinical Trial Results and Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. The SURMOUNT-1 clinical trial showed average weight loss of approximately 15% to 21% of body weight at the highest dose (15 mg weekly) over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1-only receptor agonist. The STEP-1 clinical trial showed average weight loss of approximately 15% body weight at the maximum dose (2.4 mg weekly) over 68 weeks under the same lifestyle conditions.
Key difference: Mounjaro's dual mechanism activates two hormone pathways (GIP and GLP-1), while Wegovy activates one (GLP-1 only). Individual results vary significantly, and clinical trial outcomes do not predict personal outcomes. Use our GLP-1 weight loss calculator to explore projected results at different doses based on your starting weight.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Dosing, Side Effects, and NHS Eligibility
Dosing: Mounjaro starts at 2.5 mg weekly and escalates to a maximum of 15 mg. Wegovy starts at 0.25 mg weekly and escalates to 2.4 mg maximum. Both are once-weekly injections using a pre-filled pen.
Side effects are similar between the two — nausea, diarrhoea, constipation, and stomach pain are common, particularly during dose escalation. Serious side effects are rare but require immediate medical attention.
Eligibility: Both require a BMI of 30 kg/m² or above, or 27 kg/m² with weight-related health conditions. South Asian, Chinese, Black African, or Black Caribbean adults may have different thresholds. Your prescriber will assess whether either is suitable based on your individual health profile and medical history. Calculate your BMI using our free BMI calculator to check your starting point.
- 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.
What is the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist (activates two hormone pathways), whilst Wegovy is a GLP-1-only agonist (activates one pathway). Both work to reduce appetite and support weight loss, but through slightly different mechanisms. Clinical trials suggest Mounjaro may produce slightly higher average weight loss, but individual results vary considerably.
Which one will I lose more weight with — Mounjaro or Wegovy?
Clinical trial data shows Mounjaro averaged 15–clinically studied weight loss and Wegovy around clinically studied weight loss, but these are population averages. Individual results vary significantly based on genetics, adherence, diet, and exercise. Your prescriber cannot predict your personal outcome. Both require lifestyle changes for best results.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, switching is possible and managed by your prescriber. There is no official conversion chart, but approximate equivalences exist (5 mg Mounjaro ≈ 0.5 mg Wegovy; 15 mg Mounjaro ≈ 2.4 mg Wegovy). Any switch must be done under clinical supervision — do not attempt this yourself.
Are side effects the same with both medications?
Side effect profiles are very similar. Nausea, diarrhoea, constipation, and stomach pain are most common, particularly during dose escalation. Serious side effects like pancreatitis or gallbladder issues are rare with both. Your GP or prescriber will discuss your individual risk based on your medical history.
How do I get Mounjaro or Wegovy prescribed in the UK?
Both are available through NHS specialist tier 3 weight management services (via GP referral) or through private online prescribing following a clinical assessment with a UK-licensed prescriber. NHS access varies by region and waiting times can be lengthy. Private prescription usually takes 1–2 weeks once approved.
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.