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
Does Wegovy Work As Well As Mounjaro?
Both Wegovy and Mounjaro are prescription-only weight loss injections licensed in the UK, but they work differently and show different results in clinical trials. Wegovy (semaglutide) is a GLP-1 receptor agonist, while Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist—meaning Mounjaro activates two hormone pathways instead of one. Clinical trials suggest Mounjaro may produce slightly greater average weight loss, but individual results vary significantly. Your NHS eligibility and access will depend on your local tier 3 specialist weight management service, as both are available through the NHS and private routes.
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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 NHS Evidence
The STEP-1 clinical trial (Wegovy) showed an average weight loss of approximately 14.9% of body weight over 68 weeks at the maximum 2.4 mg dose, alongside a reduced-calorie diet and increased physical activity. The SURMOUNT-1 trial (Mounjaro) demonstrated average weight loss of approximately 20.9% of body weight at the 15 mg dose over 72 weeks under similar conditions.
However, these figures come from different trials with different populations, so direct comparison has limitations. Clinical trial data shows both medications are effective for weight management in UK adults. The key difference is Mounjaro's dual mechanism—it activates both GIP and GLP-1 receptors, whereas Wegovy activates GLP-1 alone. This may explain the slightly higher average weight loss seen with Mounjaro, but individual results vary widely. Some people respond better to one medication than another. NHS specialist services will assess which is most suitable for your individual circumstances.
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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.
NHS Eligibility and Access for Both Medications
Both Wegovy and Mounjaro are available through NHS specialist tier 3 weight management services and through private prescription routes in the UK. For NHS access, you'll need referral from your GP to your local specialist weight management service—waiting times vary significantly by region. Eligibility criteria are the same for both: a BMI of 30 kg/m² or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, hypertension, or sleep apnoea.
NICE has approved both medications for NHS use, but availability depends on your integrated care board (ICB) funding. Many areas have limited NHS access due to demand. If you want to access either medication more quickly, private online prescribing following clinical assessment is an option. Use our free GLP-1 weight loss calculator to project potential outcomes at different doses, and our BMI calculator to check your eligibility criteria.
- 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 Mounjaro more effective than Wegovy?
Clinical trials suggest Mounjaro may produce slightly higher average weight loss (approximately 21% vs 15% body weight), but both are effective. The dual mechanism of Mounjaro (GIP + GLP-1) differs from Wegovy's single GLP-1 pathway. However, individual response varies—some people respond better to one medication. Your prescriber will advise which is more suitable for you.
Can the NHS prescribe both Wegovy and Mounjaro?
Yes, both are NICE-approved and available through NHS specialist tier 3 weight management services. However, availability varies by region and integrated care board (ICB). Waiting times can be lengthy. Private prescription is available if you want faster access following an online clinical assessment.
What is the difference between Mounjaro and Wegovy mechanism?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—it activates two hormone pathways. Wegovy (semaglutide) is a GLP-1 receptor agonist only—single pathway. This dual action may contribute to Mounjaro's slightly higher average weight loss in clinical trials, but both medications reduce appetite and support feeling fuller.
Which injection is better for NHS prescribing?
Both are equally valid choices on the NHS. Your GP and specialist will assess which is more appropriate based on your health history, any previous medication responses, and individual circumstances. Neither is universally "better"—effectiveness depends on the individual. Some people prefer Wegovy, others Mounjaro.
How long does it take to see results with either medication?
Most people begin noticing appetite reduction within the first few weeks, though weight loss typically becomes measurable after 4–8 weeks. Clinical trial data was collected over 12–16 weeks minimum. Both medications require ongoing use alongside a reduced-calorie diet and increased physical activity for sustained results.
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.