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 and Other Medications — How They Compare
If you're considering prescription weight loss medication in the UK, you'll likely encounter Mounjaro, Wegovy, or Saxenda. Each is a prescription-only injection licensed for weight management, but they work differently and have distinct eligibility criteria. This guide explains the key differences between Mounjaro (tirzepatide), Wegovy (semaglutide), and other options available, helping you understand which might be suitable for your situation. Remember, your GP or licensed prescriber will assess your individual health and determine the best option for you. Use our free BMI calculator above to check your current status before speaking with a healthcare professional.
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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 Mounjaro Differs From Wegovy and Other Options
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—meaning it activates two separate hormone pathways to help regulate appetite and blood sugar. Wegovy (semaglutide) is a GLP-1-only agonist, activating a single pathway. This mechanism difference may explain why clinical trials showed different average weight loss outcomes: SURMOUNT-1 showed Mounjaro participants lost approximately 15–21% body weight at varying doses, whilst STEP-1 showed Wegovy participants lost around 14.9% body weight on average. Saxenda (liraglutide) is also a GLP-1 agonist but requires daily injections rather than weekly. All three are prescription-only medicines requiring a UK-licensed prescriber's assessment. Individual results vary considerably, and no medication assures weight loss without accompanying dietary and lifestyle changes.
- Mounjaro KwikPen: once-weekly injection, doses 2.5–15 mg
- Wegovy: once-weekly injection, doses 0.25–2.4 mg
- Saxenda: once-daily injection, doses 0.6–3 mg
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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.
Suitability and Prescriber Choice — What Determines Which Is Right for You
Eligibility for any weight loss medication depends on your BMI, existing health conditions, and medical history. UK adults with a BMI of 30 or above, or 27–29.9 with weight-related conditions (such as type 2 diabetes, hypertension, or sleep apnoea), may be candidates. However, a prescriber will assess factors including your current medications, tolerance for gastrointestinal side effects, injection preferences, and previous weight loss attempts. Some individuals tolerate one medication better than another. Your prescriber might recommend Mounjaro if you have metabolic risk factors, or Wegovy if you prefer a simpler single-mechanism approach. NHS access is through specialist tier 3 weight management services; private access is available through licensed online prescribers. Try 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.
Is Mounjaro more effective than Wegovy?
Clinical trials showed Mounjaro participants achieved average weight loss of 15–21% body weight, whilst Wegovy showed approximately 14.9% average loss. However, individual results vary significantly. Neither medication is universally "more effective"—suitability depends on your personal health profile, which a prescriber will assess.
What's the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist (two hormone pathways), whilst Wegovy is a GLP-1-only agonist (single pathway). Both are once-weekly injections. The dual mechanism may account for slightly different clinical outcomes, but both require prescription and clinical assessment.
Can I switch from Wegovy to Mounjaro?
Yes, prescribers can switch between medications if clinically appropriate. Approximate dose equivalence exists (e.g., Wegovy 2.4 mg ≈ Mounjaro 10–15 mg), but any switch must be managed by your prescriber—never self-switch without guidance.
How do I access Mounjaro or Wegovy on the NHS in the UK?
NHS access is through specialist tier 3 weight management services. You'll need a GP referral and assessment. Waiting times vary significantly by region. Private online prescribing is also available through GPhC-registered pharmacies following an online clinical assessment.
Which medication has fewer side effects?
Both share common side effects (nausea, diarrhoea, constipation). Individual tolerance varies. Gastrointestinal side effects tend to be more frequent early in treatment and may improve over time. Your prescriber will discuss your personal risk factors when choosing the most suitable option.
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.