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 vs Wegovy — Which is Right for You?
Both Mounjaro and Wegovy are prescription-only weight management injections licensed in the UK, but they work differently and may suit different individuals. Mounjaro (tirzepatide) uses a dual GIP and GLP-1 mechanism, whilst Wegovy (semaglutide) is a GLP-1-only medication. Clinical trials show both can help with weight loss when used alongside dietary changes and increased physical activity, but the choice between them depends on individual health factors and prescriber assessment. This guide compares them factually so you understand the key differences.
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.
How Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. It activates two natural hormone pathways simultaneously — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) — which may support appetite regulation, reduce cravings, and help with feeling fuller after smaller meals.
Wegovy (semaglutide) activates only the GLP-1 pathway. It works by signalling fullness to the brain and slowing how quickly food leaves the stomach.
In the SURMOUNT-1 clinical trial, Mounjaro users lost an average of 20.9% body weight at the maximum 15 mg dose over 72 weeks. In the STEP-1 clinical trial, Wegovy users lost approximately 14.9% body weight at 2.4 mg over 68 weeks. However, individual results vary significantly — these are trial averages, not assured outcomes. Both medications are used alongside a reduced-calorie diet and increased physical activity for best results.
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.
Doses, Side Effects, and Suitability
Mounjaro starts at 2.5 mg weekly and escalates to a maximum of 15 mg. Wegovy starts at 0.25 mg and reaches a maximum of 2.4 mg. Both are once-weekly injections.
Common side effects of both include nausea, diarrhoea, vomiting, and constipation — these often improve over time. A prescriber will assess your medical history, current medications (especially oral contraceptives and diabetes drugs), and health conditions to determine which is more suitable for you. Your GP or a licensed prescriber can evaluate whether either medication is appropriate for your individual circumstances and help you choose based on your health profile and treatment goals.
- 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's the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist (two hormone pathways), whilst Wegovy is GLP-1 only (single pathway). Clinical trials suggest Mounjaro may help some users lose more weight on average, but individual results vary. The choice depends on your health profile and prescriber assessment.
Which one will help me lose more weight?
Clinical trial data shows Mounjaro users lost approximately 20.9% body weight on average, whilst Wegovy users lost approximately 14.9%. However, these are trial averages — your individual results may differ significantly. Factors like diet, activity, genetics, and adherence all influence weight loss outcomes.
Are the side effects the same?
Both medications share similar common side effects: nausea, diarrhoea, vomiting, and constipation. Side effect severity varies between individuals. Your prescriber can discuss which medication may suit you better based on your medical history and tolerability profile.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medications should only be done under prescriber guidance. Whilst approximate dose equivalences exist (based on clinical practice), there is no official conversion chart. Any switch requires reassessment and a new prescription from your GP or licensed prescriber.
How do I know which one is right for me?
Neither medication is "better" — suitability is individual. A prescriber will assess your BMI, weight-related health conditions, current medications, and medical history to recommend the most appropriate option. Both require a clinical assessment and prescription. Use our free GLP-1 weight loss calculator to explore projected weight loss, then discuss options with your prescriber.
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.