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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Wegovy vs Mounjaro: UK Comparison Guide
Wegovy and Mounjaro are both prescription-only weight loss injections available in the UK, but they work differently and suit different people. This guide compares the two medications factually — their mechanisms, clinical trial results, doses, side effects, and how prescribers decide which is right for you. Both require a clinical assessment and medical prescription. Individual results vary significantly between people.
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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 Wegovy and Mounjaro Work Differently
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates one hormone pathway in the body to reduce appetite and help you feel fuller after eating smaller meals. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways, which is why it has a different mechanism and different clinical trial results.
In the UK, Wegovy starts at 0.25 mg and increases to a maximum of 2.4 mg once weekly. Mounjaro starts at 2.5 mg and goes up to 15 mg once weekly. Both slow gastric emptying, but Mounjaro's dual action may offer a different effect profile. The clinical evidence shows Mounjaro produced slightly higher average weight loss in trials (around 15–21% body weight) compared to Wegovy (around 15% body weight), though individual responses vary considerably.
- Wegovy: GLP-1 only, single mechanism
- Mounjaro: GLP-1 + GIP, dual mechanism
- Both: once-weekly injection, prescription-only
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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.
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Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Which Medication Is Right for You?
Your GP or prescriber will assess your individual health, medical history, preferences, and previous treatment responses to decide which medication is appropriate. Neither Wegovy nor Mounjaro is "better" — they are different tools for different people. Your prescriber considers your BMI, weight-related health conditions, other medications, and whether you have ever used similar medications before.
Both medications require a clinical assessment and ongoing monitoring. Access in the UK is through NHS specialist tier 3 weight management services (with potential waiting lists) or private online prescribing following an assessment. Both are used alongside reduced-calorie diet and increased physical activity — medication alone is not sufficient. Use our GLP-1 weight loss calculator and BMI calculator to understand your starting point, then discuss prescription options with a licensed prescriber.
Common side effects of both include nausea, diarrhoea, constipation, and stomach pain — usually mild and temporary. Serious side effects are rare but require medical attention. If you have a history of pancreatitis, gallbladder problems, or certain cancers in your family, discuss this with your prescriber before starting either medication. Wegovy and Mounjaro should not be used in pregnancy or whilst breastfeeding.
- 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.
Can I switch from Wegovy to Mounjaro or vice versa in the UK?
Yes, prescribers can switch between them, but this must be managed medically. There is no official conversion chart — any switch requires clinical assessment and appropriate dose adjustment. Never self-switch medications. Discuss with your prescriber if you feel one is not working well for you.
Which medication causes more side effects?
Both have similar common side effects (nausea, diarrhoea, constipation). Individual tolerance varies. Some people tolerate one better than the other. Side effects usually reduce over time as the body adjusts. Your prescriber will monitor you and adjust the dose if needed.
Does the NHS prescribe Wegovy or Mounjaro?
Yes, both are available on the NHS through tier 3 specialist weight management services following NICE guidance. However, availability varies significantly by region, and waiting lists can be lengthy. Private online prescribing offers faster access for those who meet eligibility criteria and can afford it.
How much weight will I lose with Wegovy or Mounjaro?
Clinical trials show average weight loss of 14–21% of body weight over several months alongside diet and exercise. However, individual results vary considerably — some people lose more, some less. Your specific outcome depends on many factors including starting weight, adherence, diet, and exercise.
Is Mounjaro stronger than Wegovy?
"Stronger" is misleading — they have different mechanisms. Mounjaro's dual GIP+GLP-1 action produced slightly higher average weight loss in trials, but Wegovy may suit some people better. Your prescriber will consider which is more appropriate for your specific situation, not which is universally "stronger."
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.