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 vs Wegovy: What's the Difference?
Both Mounjaro and Wegovy are prescription-only weight loss injections available in the UK, but they work differently and have distinct dosing schedules. Mounjaro (tirzepatide) uses a dual GIP and GLP-1 mechanism, whilst Wegovy (semaglutide) activates GLP-1 alone. This guide compares both medications side-by-side to help you understand how they differ in terms of how they work, their doses, expected results, and UK eligibility. Both require a clinical assessment before prescription and are typically used alongside diet and lifestyle changes. Use our GLP-1 weight loss calculator to explore potential outcomes with either medication.
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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 Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in the body. This dual mechanism may help regulate appetite more comprehensively and support feeling fuller after meals. Wegovy (semaglutide) activates only the GLP-1 pathway. Both slow gastric emptying and reduce food cravings, but Mounjaro's dual action is theoretically a more powerful approach — though individual results vary significantly.
- Mounjaro: GIP + GLP-1 agonist; once-weekly injection; doses 2.5–15 mg
- Wegovy: GLP-1 agonist only; once-weekly injection; doses 0.25–2.4 mg
- Starting point: Mounjaro begins at 2.5 mg; Wegovy begins at 0.25 mg
- Escalation: Both require minimum 4 weeks at each dose before increasing
Neither medication is insulin. Both help the body regulate blood sugar and appetite, but work through different biological pathways.
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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
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Weight Loss Results and UK Eligibility
Clinical trials show both medications support meaningful weight loss. Mounjaro clinical trials (SURMOUNT-1) showed average weight loss of 15–21% of body weight over 72 weeks at maximum dose. Wegovy trials (STEP-1) showed average weight loss of approximately 15% at maximum dose over 68 weeks. Important: These are trial averages — individual results vary, and outcomes depend on dose, diet, activity level, and individual metabolism.
In the UK, both Mounjaro and Wegovy are eligible for adults with BMI ≥30, or BMI 27–29.9 with weight-related health conditions (type 2 diabetes, hypertension, dyslipidaemia, sleep apnoea, or cardiovascular disease history). South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds. Access is available through NHS specialist tier 3 services (longer waiting lists) or private online prescribing services. Your prescriber will assess individual suitability during 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.
Which medication causes more side effects, Mounjaro or Wegovy?
Both cause similar common side effects — nausea, diarrhoea, vomiting, and constipation. Side effect profiles are comparable. Nausea is most common in early weeks and often decreases as the body adjusts. Individual tolerance varies. Your prescriber can discuss which medication may be more suitable for you based on your health history.
Can I switch from Wegovy to Mounjaro, or vice versa?
Yes, switching is possible, but must be managed by your prescriber. Mounjaro 5 mg is approximately equivalent to Wegovy 0.5 mg; Mounjaro 10 mg to Wegovy 1.7 mg; and Mounjaro 15 mg to Wegovy 2.4 mg. However, no official conversion chart exists — any switch requires clinical oversight and may involve a washout period. Always consult your GP or prescriber before changing medications.
Is Mounjaro more effective than Wegovy for weight loss?
Clinical trial data suggests Mounjaro may support slightly greater average weight loss (up to 21% vs 15%), but differences are modest and individual results vary widely. Some people respond better to Wegovy; others respond better to Mounjaro. The "best" medication is the one your prescriber assesses as most suitable for your individual health profile and that you tolerate well.
How do I get Mounjaro or Wegovy in the UK?
Both are prescription-only and require a clinical assessment. Through the NHS, you'll need referral to a tier 3 specialist weight management service — availability and waiting times vary by region. Privately, you can access online consultations with UK-licensed prescribers through GPhC-registered pharmacies. Private prescriptions typically cost £129–£320 per month depending on dose. Calculate your potential results using our free GLP-1 weight loss calculator.
Is there a difference in cost between Mounjaro and Wegovy in the UK?
Pricing varies by provider and dose. Mounjaro KwikPen and Wegovy auto-injection pens are similarly priced on private prescriptions, ranging approximately £130–£320 monthly depending on your chosen dose and provider. NHS availability depends on your region and specialist service. Prices vary — check with your local pharmacy or prescriber for exact costs specific to your dose and location.
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.