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: Real UK Experiences & Key Differences
Both Mounjaro and Wegovy are prescription-only weight loss injections available in the UK, but they work differently and produce different results in clinical trials. Understanding how each medication functions, what users typically experience, and who they're suitable for can help you have an informed conversation with your GP or prescriber about which might be right for you. This guide compares both medications based on clinical evidence and UK prescribing information, not individual testimonials.
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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 They Work Differently: GLP-1 vs Dual GIP+GLP-1
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates a single hormone pathway that helps reduce appetite and increase feelings of fullness. The STEP clinical trials showed Wegovy participants lost an average of around 14.9% of their body weight over 68 weeks at the maximum dose of 2.4 mg.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways simultaneously. This dual mechanism is the key difference. The SURMOUNT clinical trials showed Mounjaro participants lost an average of 15% to 20.9% of their body weight depending on dose (5 mg to 15 mg) over 72 weeks. Because Mounjaro targets two pathways, some users report stronger appetite suppression in their experiences, though individual responses vary significantly.
- Wegovy: single pathway activation, proven safe track record (approved for diabetes as Ozempic for many years)
- Mounjaro: dual pathway activation, newer medication (approved 2024 in UK for weight management)
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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.
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Side Effects & Suitability: What Users Typically Report
Both medications commonly cause nausea, diarrhoea, constipation, and stomach pain — especially in the first weeks. Many users find these side effects reduce as their body adjusts. Mounjaro's dual mechanism may cause slightly stronger initial side effects for some users, though clinical data shows both have similar tolerability overall.
Eligibility is the same for both: BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Your prescriber will assess which is more suitable based on your individual health, medical history, and any other medications you take. Both are prescription-only and require a clinical assessment — your GP or a licensed online prescriber will make the recommendation based on your personal circumstances, not your preference alone.
Use our free GLP-1 weight loss calculator to explore potential weight loss projections at different doses with either medication, and check your BMI using our free BMI calculator to understand your starting point.
- 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 stronger than Wegovy?
Mounjaro's dual mechanism (GIP + GLP-1) versus Wegovy's single mechanism (GLP-1 only) means Mounjaro has shown slightly higher average weight loss in clinical trials — around 20.9% at maximum dose versus 14.9% for Wegovy. However, individual results vary considerably. Your prescriber chooses based on your health profile, not on which is "stronger."
Why would a prescriber choose Wegovy over Mounjaro?
Wegovy has a longer safety record (semaglutide has been used for type 2 diabetes since 2009). Some prescribers may recommend it for patients with certain health conditions, if you've previously tolerated semaglutide, or based on availability and cost. Mounjaro is newer in the UK market (2024) for weight management, so some patients may be prescribed Wegovy first while more experience with Mounjaro accumulates.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (doses up to 2 mg) while Wegovy is licensed specifically for weight management (doses up to 2.4 mg). In the UK, Ozempic is not licensed for weight loss — Wegovy is the correct licensed option if weight management is the goal.
Can you switch from Mounjaro to Wegovy or vice versa?
Switching between these medications requires your prescriber's guidance. The doses are not directly equivalent (approximate conversion: Mounjaro 5 mg ≈ Wegovy 0.5 mg, Mounjaro 15 mg ≈ Wegovy 2.4 mg). Any change must be managed clinically — never stop one and start the other without prescriber support.
How do I get Mounjaro or Wegovy prescribed in the UK?
You can be referred to your local NHS tier 3 weight management service by your GP, though waiting lists vary by region. Alternatively, private online prescribers can assess you for either medication if you meet eligibility criteria (BMI 30+ or 27+ with weight-related conditions). Both routes require a clinical assessment — neither medication is available without a prescription.
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