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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Wegovy Or Mounjaro: Understanding The Differences
Choosing between Wegovy and Mounjaro can be confusing — both are prescription-only weight loss injections available in the UK, but they work differently and may suit different people. Wegovy (semaglutide) is a single-hormone GLP-1 agonist, while Mounjaro (tirzepatide) activates two hormone pathways: GIP and GLP-1. Both are licensed for weight management in UK adults, though clinical trial results and individual eligibility vary. This guide explains the key differences to help you understand your options. Use our GLP-1 weight loss calculator to explore potential outcomes, and always consult your GP or a prescriber to determine which is suitable for your situation.
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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 — Key Differences
Wegovy (semaglutide) activates the GLP-1 receptor, a single hormone pathway that helps regulate appetite, reduce food cravings, and slow gastric emptying. The STEP clinical trials showed participants lost an average of approximately 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 — meaning it activates two hormone systems simultaneously. This dual mechanism may provide greater appetite suppression and support for feeling fuller sooner. SURMOUNT trial data showed average weight loss of approximately 15–21% of body weight, with the 15 mg dose showing around clinically studied weight loss at 72 weeks.
In direct terms, both medications have shown meaningful weight loss in clinical trials. Individual results vary significantly, and which works better depends on your personal metabolism, medical history, and how you respond to treatment.
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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.
Dosing, Access, And Practical Considerations
Dosing differences: Wegovy starts at 0.25 mg and increases to a maximum of 2.4 mg (once weekly). Mounjaro starts at 2.5 mg and increases to a maximum of 15 mg (also once weekly). Mounjaro has more dose flexibility, which may allow prescribers to fine-tune your treatment.
UK access: Both are available through NHS specialist tier 3 weight management services (though availability is regional and waiting lists vary) and through private online prescribing following a clinical assessment. Neither can be prescribed by a standard GP practice without specialist involvement.
Cost: Private costs typically range from £129–£320 monthly depending on dose. Both require ongoing prescription and clinical monitoring. Once you stop either medication, weight regain is possible, so they are intended as long-term management tools alongside lifestyle changes.
- 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 for weight loss?
Clinical trials show Mounjaro produced slightly higher average weight loss (up to 20.9% at maximum dose) compared to Wegovy (approximately 14.9%), but individual results vary substantially. Some people respond better to one than the other. Your prescriber will assess which is more suitable based on your health profile, not just average trial data.
Can I switch from Wegovy to Mounjaro if Wegovy doesn't work well?
Yes, switching is possible, though it must be managed by your prescriber. There is no official conversion chart, but approximate equivalence exists (for example, Wegovy 2.4 mg is roughly equivalent to Mounjaro 15 mg). Any switch requires stopping one medication and managing a transition period safely.
Which injection is easier to use — Wegovy or Mounjaro?
Both are once-weekly injections using pre-filled pens, so convenience is very similar. Wegovy uses an auto-injection pen; Mounjaro uses a KwikPen. Neither requires assembly. Choice between them is unlikely to depend on administration difficulty.
What if I'm eligible for neither Wegovy nor Mounjaro?
If you don't meet criteria for either medication, your GP may recommend Saxenda (liraglutide), a daily GLP-1 injection, or direct you to NHS tier 2 or tier 3 weight management services for other evidence-based support including dietary advice and structured exercise programmes.
Do I need to diet and exercise if I take Wegovy or Mounjaro?
Yes — both medications are most effective when combined with a reduced-calorie diet and increased physical activity. Clinical trials showed results using this combination. Medication alone without lifestyle changes is less effective. Use our BMI calculator to track your baseline and monitor progress alongside behavioural changes.
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.