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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Mounjaro Injection Reviews vs Wegovy — What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK. If you're researching which weekly weight loss injection might suit you, understanding the key differences between them is important. This guide compares clinical trial results, how they work, doses, and side effects to help you understand what prescribers consider when assessing your suitability. Remember, individual results vary significantly, and the right medication depends on your personal health profile.
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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.
Clinical Trial Results and How They Work
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways. In the SURMOUNT-1 clinical trial, participants achieved an average weight loss of approximately 15% to 20.9% of body weight over 72 weeks, depending on dose — with the 15 mg Mounjaro KwikPen dose achieving the highest average loss.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. In the STEP-1 clinical trial, participants achieved an average weight loss of approximately 14.9% of body weight at the maximum 2.4 mg dose over 68 weeks.
- Mounjaro's dual mechanism may offer slightly stronger appetite suppression for some people
- Wegovy's single mechanism is well-established and has longer real-world use data
- Both are used alongside reduced-calorie diet and increased physical activity
- Results are highly individual — some people respond better to one than the other
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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.
Which Injection Is Right for You?
The choice between Mounjaro and Wegovy isn't about one being "better" — it's about what suits your individual health profile. Your GP or prescriber will assess factors including your BMI, weight-related health conditions, current medications, and any contraindications. Both medications require a UK prescription and clinical assessment before being dispensed. You can access these via NHS specialist weight management services (though availability and waiting times vary by region) or through private online prescribing following a clinical assessment.
Try our free GLP-1 weight loss calculator above to explore potential weight loss outcomes at different doses for both medications. Use our BMI calculator to check where you sit on NHS guidelines, which helps prescribers assess your eligibility.
- 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+GLP-1 agonist (two hormone pathways), while Wegovy is a GLP-1 agonist only (one pathway). This dual mechanism in Mounjaro may provide stronger appetite suppression for some people, but Wegovy's single mechanism is equally effective for many others. Individual response varies.
Did Mounjaro show more weight loss than Wegovy in trials?
Clinical trials showed Mounjaro achieved slightly higher average weight loss (up to 20.9%) compared to Wegovy (14.9%), but these trials were different studies with different populations. Real-world results vary significantly between individuals, and many people lose substantial weight on either medication.
How often do I inject Mounjaro versus Wegovy?
Both are once-weekly injections. Mounjaro comes in a KwikPen with doses ranging from 2.5 mg to 15 mg. Wegovy ranges from 0.25 mg to 2.4 mg. Your prescriber will determine the right starting dose and escalation schedule based on your health profile.
Are the side effects of Mounjaro and Wegovy different?
Both cause similar common side effects: nausea, diarrhoea, constipation, and stomach pain — typically most noticeable when starting or increasing doses. Side effect profiles are comparable. Your prescriber will discuss what to expect and how to manage them.
How do I get Mounjaro or Wegovy prescribed in the UK?
Both require a UK prescription following clinical assessment. You can access them through NHS specialist tier 3 weight management services (via GP referral, with variable waiting times by region) or through private online prescribing with a UK-licensed prescriber. Eligibility typically requires BMI ≥30, or ≥27 with weight-related health conditions.
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.