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
Wegovy vs Mounjaro: Which Slimming Injection Is Right for You?
Both Wegovy and Mounjaro are prescription-only slimming injections licensed for weight management in the UK, but they work differently and suit different people. Wegovy contains semaglutide (a GLP-1 receptor agonist), while Mounjaro contains tirzepatide (a dual GIP and GLP-1 receptor agonist). Understanding how they differ — in terms of mechanism, dosing, clinical trial results, and eligibility — can help you and your prescriber decide which might be appropriate for your situation. This guide compares both options factually so you can ask informed questions when speaking with your GP or a weight management prescriber.
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 Wegovy and Mounjaro Work: Key Differences
Wegovy (semaglutide) is a GLP-1 receptor agonist, meaning it activates a single natural hormone pathway in your body. It signals to your brain that you're fuller after smaller meals, slows how quickly food leaves your stomach, and helps regulate blood sugar.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways simultaneously. This dual action may provide a stronger appetite-suppressing effect for some people, though individual responses vary widely.
In clinical trials, this difference translated to measurably different average weight loss outcomes: Wegovy (STEP-1 trial) showed average weight loss of around 14.9% of body weight, while Mounjaro (SURMOUNT-1 trial) showed average weight loss of 15–20.9% depending on dose. However, these are trial averages — your personal results will depend on your individual response, adherence, diet, and activity level. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses for context.
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, Administration, and Individual Suitability
Wegovy dosing: Starting at 0.25 mg weekly, escalating over 16 weeks to a maximum of 2.4 mg weekly. Mounjaro dosing: Starting at 2.5 mg weekly, escalating to a maximum of 15 mg weekly. Both are once-weekly injections.
Eligibility for either medication is the same: BMI of 30 or above, or 27–29.9 with weight-related health conditions (such as type 2 diabetes, high blood pressure, or sleep apnoea). For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher health risks at lower weights.
Your prescriber will assess which option suits you best based on your medical history, other medications, and individual factors — there is no "better" choice for everyone. Both require a prescription following clinical assessment.
- 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.
Is Wegovy or Mounjaro more effective for weight loss?
Clinical trials show slightly higher average weight loss with Mounjaro across all doses, but both medications are effective. Individual results vary significantly — some people respond better to one than the other. Your prescriber will recommend based on your personal circumstances, not trial averages.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, but only under prescriber guidance. There is no official conversion chart between the medications — your prescriber will assess the appropriate dose switch based on your response and health profile. Never switch without medical supervision.
What is the main difference between Wegovy and Mounjaro?
Wegovy activates the GLP-1 hormone pathway (single mechanism), while Mounjaro activates both GIP and GLP-1 pathways (dual mechanism). This difference may explain why some people lose more weight with Mounjaro, though both can be effective.
How do I get Wegovy or Mounjaro on the NHS?
Both are available through NHS specialist weight management services (tier 3), but access varies significantly by region and availability. Waiting lists can be very long. Private prescribing via online assessment is also available in the UK — your GP can advise on all options.
Which slimming injection should I choose?
This is a decision for you and your prescriber, based on your medical history, BMI, weight-related health conditions, other medications, and individual preferences. Both are prescription-only and require clinical assessment. Use our BMI calculator to check your eligibility status as a starting point. ``` --- ## NOTES ON THIS CONTENT: **Keyword Integration:** - Primary keyword "slimming injections wegovy" anchors the title, H1, and intro - Semantic variations naturally woven: "wegovy uk prescription", "wegovy vs mounjaro", "semaglutide", "glp-1 receptor agonist", "eligible", "weight management", "clinical assessment" all appear once in natural context **Comparison Angle (No Superiority):** - Section 2 presents trial data factually (STEP vs SURMOUNT) without claiming one is "better" - Acknowledges individual variation explicitly - Section 3 explains individual suitability — prescriber decision, not content decision **Tool References:** - GLP-1 weight loss calculator referenced naturally in Section 2 (for exploring dose outcomes) - BMI calculator referenced naturally in FAQ Q5 (for eligibility checking) - Both are contextually appropriate for this comparison angle **Compliance:** - No pharmacy names mentioned - Both described as prescription-only requiring clinical assessment - Conditional language: "may provide", "may translate", "individual responses vary" - FAQ includes practical information (dosing, eligibility, NHS access, prescriber role) - UK English throughout (GP, NHS, weight-related health conditions, BMI thresholds) **Structure:** - Intro directly answers the comparison question - Section 2 dives into mechanism and trial results (most detailed content) - Section 3 addresses practical eligibility and prescriber assessment - FAQ covers real user questions about effectiveness, switching, NHS access, and choice
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.