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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What's the Difference Between Mounjaro and Wegovy Ingredients?
Mounjaro and Wegovy are both prescription weight loss injections available in the UK, but they contain different active ingredients that work in different ways. Mounjaro contains tirzepatide, a dual GIP and GLP-1 receptor agonist, while Wegovy contains semaglutide, a GLP-1 receptor agonist only. Understanding these differences can help you and your prescriber decide which medication might be most suitable for your circumstances. Both require clinical assessment before prescription.
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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.
Active Ingredients and How They Work
Mounjaro (tirzepatide) is a dual receptor agonist, meaning it activates two separate hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism may help regulate appetite more effectively than a single pathway.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating just the GLP-1 pathway. Both medications help you feel fuller after smaller meals and reduce food cravings.
The key difference is the mechanism: Mounjaro's dual action targets two hormone systems, while Wegovy's single mechanism focuses on GLP-1 alone. Clinical trials show both deliver meaningful weight loss results, though the dual mechanism of tirzepatide may provide additional metabolic benefits in some patients.
- Mounjaro: Dual GIP + GLP-1 agonist
- Wegovy: GLP-1 agonist only
- Both are once-weekly injections
- Both require prescription and clinical assessment
Clinically BackedWeight Loss
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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.
Clinical Trial Results and Individual Suitability
Clinical trials showed different outcomes for each medication. In the SURMOUNT trials, Mounjaro achieved average weight loss of approximately 15–21% of body weight, depending on dose. In the STEP trials, Wegovy achieved average weight loss of approximately 15% of body weight. However, individual results vary significantly, and neither medication assures specific outcomes.
Which medication is right for you depends on your personal health circumstances, other medications you take, and your prescriber's clinical judgment. Both are prescription-only and require assessment by a UK-licensed prescriber. Your GP or a private prescriber can help determine which is more suitable based on your medical history, current medications, and weight loss goals. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses.
- 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 active ingredient in Mounjaro?
Mounjaro's active ingredient is tirzepatide, a dual GIP and GLP-1 receptor agonist. It activates two natural hormone pathways in the body to help regulate appetite and support weight loss. Tirzepatide is manufactured by Eli Lilly and is available as a once-weekly injection in the UK.
What is the main active ingredient in Wegovy?
Wegovy's active ingredient is semaglutide, a GLP-1 receptor agonist. It activates the GLP-1 hormone pathway to help reduce appetite and support feelings of fullness. Semaglutide is manufactured by Novo Nordisk and is available as a once-weekly injection licensed for weight management in the UK.
Why does Mounjaro have two ingredients and Wegovy only one?
Mounjaro doesn't have two separate ingredients — it's one active ingredient (tirzepatide) that targets two receptor pathways. Wegovy targets one pathway (GLP-1). This difference in mechanism means they work slightly differently in the body, which is why some patients may respond better to one than the other.
Which works better, Mounjaro or Wegovy?
Both medications can help support weight loss, but individual results vary. Clinical trials showed slightly higher average weight loss with Mounjaro, but this doesn't mean it will work better for every person. Suitability depends on your personal health circumstances, other medications, and prescriber assessment. Neither is universally "better."
Can you switch from Wegovy to Mounjaro or vice versa?
Switching between medications is possible but must be managed by your prescriber. There's no official conversion chart — any switch requires stopping one medication and starting another with appropriate clinical oversight. Never switch without speaking to your GP or prescriber 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.